IF Diversity Receiver
Data Sheet
AD6655
Rev. B Document Feedback
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FEATURES
SNR = 74.5 dBc (75.5 dBFS) in a 32.7 MHz BW at
70 MHz at 150 MSPS
SFDR = 80 dBc to 70 MHz at 150 MSPS
1.8 V analog supply operation
1.8 V to 3.3 V CMOS output supply or 1.8 V LVDS
output supply
Integer 1-to-8 input clock divider
Integrated dual-channel ADC
Sample rates up to 150 MSPS
IF sampling frequencies to 450 MHz
Internal ADC voltage reference
Integrated ADC sample-and-hold inputs
Flexible analog input range: 1 V p-p to 2 V p-p
ADC clock duty cycle stabilizer
95 dB channel isolation/crosstalk
Integrated wideband digital downconverter (DDC)
32-bit complex, numerically controlled oscillator (NCO)
Decimating half-band filter and FIR filter
Supports real and complex output modes
Fast attack/threshold detect bits
Composite signal monitor
Energy-saving power-down modes
APPLICATIONS
Communications
Diversity radio systems
Multimode digital receivers (3G)
TD-SCDMA, WiMax, WCDMA,
CDMA2000, GSM, EDGE, LTE
I/Q demodulation systems
Smart antenna systems
General-purpose software radios
Broadband data applications
PRODUCT HIGHLIGHTS
1. Integrated dual, 14-bit, 150 MSPS ADC.
2. Integrated wideband decimation filter and 32-bit
complex NCO.
3. Fast overrange detect and signal monitor with serial output.
4. Proprietary differential input maintains excellent SNR
performance for input frequencies up to 450 MHz.
5. Flexible output modes, including independent CMOS,
interleaved CMOS, IQ mode CMOS, and interleaved LVDS.
6. SYNC input allows synchronization of multiple devices.
7. 3-bit SPI port for register programming and register readback.
FUNCTIONAL BLOCK DIAGRAM
06709-001
AVDD FD[0:3]A DVDD DRVDD
AD6655
VIN+A
VIN–A
VREF
SENSE
CML
RBIAS
SHA
SYNC FD[0:3]B SMI
SDFS SMI
SCLK/
PDWN
SMI
SDO/
OEB
REF
SELECT
ADC
I
Q
Q
I
VIN–B
VIN+B
D13A
D0A
CLK+
CLK–
DCOA
DCOB
D13B
D0B
SHA ADC
MULTI-CHIP
SYNC
SIGNAL
MONITOR
DIV IDE 1
TO 8
DUTY
CYCLE
STABILIZER
AGND
SIGNAL MONITOR
INTERFACE
CMOS/LVDS
OUTPUT BUFFER
SIGNAL MONITOR
DATA
SDIO/
DCS SCLK/
DFS CSB DRGND
SPI
PRO GRAMMING DATA
FD BITS/THRESHOLD
DETECT
FD BITS/THRESHOLD
DETECT
32-BIT
TUNING
NCO
fADC
/8
NCO
LP/HP
DECIMATING
HB FILTER +
FIR
LP/HP
DECIMATING
HB FILTER +
FIR
CMOS
OUTPUT BUFFER
DCO
GENERATION
NOTES
1.P IN NAME S ARE FO R THE CM OS PIN CO NFI GURAT IO N ONLY ; S E E FI GURE 10 FO R LVDS P IN NAME S .
Figure 1.
AD6655 Data Sheet
Rev. B | Page 2 of 84
TABLE OF CONTENTS
Features .............................................................................................. 1
Applications ....................................................................................... 1
Product Highlights ........................................................................... 1
Functional Block Diagram .............................................................. 1
Revision History ............................................................................... 3
General Description ......................................................................... 4
Specifications ..................................................................................... 5
ADC DC Specifications—AD6655-80/AD6655-105 .............. 5
ADC DC Specifications—AD6655-125/AD6655-150 ............ 6
ADC AC Specifications—AD6655-80/AD6655-105 ............... 7
ADC AC Specifications—AD6655-125/AD6655-150 ............. 8
Digital Specifications—AD6655-80/AD6655-105 ................... 9
Digital Specifications—AD6655-125/AD6655-150 ............... 11
Switching Specifications—AD6655-80/AD6655-105 ............ 13
Switching Specifications—AD6655-125/AD6655-150 ......... 14
Timing Specifications ................................................................ 15
Absolute Maximum Ratings .......................................................... 18
Thermal Characteristics ............................................................ 18
ESD Caution ................................................................................ 18
Pin Configurations and Function Descriptions ......................... 19
Equivalent Circuits ......................................................................... 23
Typical Performance Characteristics ........................................... 24
Theory of Operation ...................................................................... 29
ADC Architecture ...................................................................... 29
Analog Input Considerations .................................................... 29
Voltage Reference ....................................................................... 31
Clock Input Considerations ...................................................... 32
Power Dissipation and Standby Mode ..................................... 34
Digital Outputs ........................................................................... 35
Digital Downconverter .................................................................. 37
Downconverter Modes .............................................................. 37
Numerically Controlled Oscillator (NCO) ............................. 37
Half-Band Decimating Filter and FIR Filter ........................... 37
fADC/8 Fixed-Frequency NCO ................................................... 37
Numerically Controlled Oscillator (NCO) ................................. 38
Frequency Translation ............................................................... 38
NCO Synchronization ............................................................... 38
Phase Offset ................................................................................. 38
NCO Amplitude and Phase Dither .......................................... 38
Decimating Half-Band Filter and FIR filter ................................ 39
Half-Band Filter Coefficients .................................................... 39
Half-Band Filter Features .......................................................... 39
Fixed-Coefficient FIR Filter ...................................................... 39
Synchronization .......................................................................... 40
Combined Filter Performance .................................................. 40
Final NCO ................................................................................... 40
ADC Overrange and Gain Control .............................................. 41
Fast Detect Overview ................................................................. 41
ADC Fast Magnitude ................................................................. 41
ADC Overrange (OR) ................................................................ 42
Gain Switching ............................................................................ 42
Signal Monitor ................................................................................ 44
Peak Detector Mode................................................................... 44
RMS/MS Magnitude Mode ....................................................... 44
Threshold Crossing Mode ......................................................... 45
Additional Control Bits ............................................................. 45
DC Correction ............................................................................ 45
Signal Monitor SPORT Output ................................................ 46
Channel/Chip Synchronization .................................................... 47
Serial Port Interface (SPI) .............................................................. 48
Configuration Using the SPI ..................................................... 48
Hardware Interface ..................................................................... 48
Configuration Without the SPI ................................................ 49
SPI Accessible Features .............................................................. 49
Memory Map .................................................................................. 50
Reading the Memory Map Register Table ............................... 50
Memory Map Register Table ..................................................... 51
Memory Map Register Description ......................................... 55
Applications Information .............................................................. 59
Design Guidelines ...................................................................... 59
Evaluation Board ............................................................................ 61
Power Supplies ............................................................................ 61
Input Signals................................................................................ 61
Output Signals ............................................................................ 61
Default Operation and Jumper Selection Settings ................. 62
Alternative Clock Configurations ............................................ 62
Alternative Analog Input Drive Configuration...................... 63
Schematics ................................................................................... 64
Data Sheet AD6655
Rev. B | Page 3 of 84
Evaluation Board Layouts .......................................................... 74
Bill of Materials ........................................................................... 82
Outline Dimensions ........................................................................ 84
Ordering Guide ........................................................................... 84
REVISION HISTORY
1/14—Rev. A to Rev. B
Removed CP-63-3 Package ............................................... Universal
Changes to Address 0x0D, Table 29 .............................................. 52
Changes to Memory Map Description Section ........................... 55
Updated Outline Dimensions ........................................................ 84
9/09—Rev. A to Rev. 0
Added Exposed Pad Notation to Figure 9 and Table 12 ............ 19
Added Exposed Pad Notation to Figure 10 and Table 13 .......... 21
Updated Outline Dimensions ........................................................ 84
Changes to Ordering Guide ........................................................... 85
11/07—Revision 0: Initial Version
AD6655 Data Sheet
Rev. B | Page 4 of 84
GENERAL DESCRIPTION
The AD6655 is a mixed-signal intermediate frequency (IF) receiver
consisting of dual 14-bit, 80 MSPS/105 MSPS/125 MSPS/150 MSPS
ADCs and a wideband digital downconverter (DDC). The AD6655
is designed to support communications applications where low
cost, small size, and versatility are desired.
The dual ADC core features a multistage, differential pipelined
architecture with integrated output error correction logic. Each
ADC features wide bandwidth differential sample-and-hold
analog input amplifiers supporting a variety of user-selectable
input ranges. An integrated voltage reference eases design consid-
erations. A duty cycle stabilizer is provided to compensate for
variations in the ADC clock duty cycle, allowing the converters
to maintain excellent performance.
ADC data outputs are internally connected directly to the digital
downconverter (DDC) of the receiver, simplifying layout and
reducing interconnection parasitics. The digital receiver has two
channels and provides processing flexibility. Each receive channel
has four cascaded signal processing stages: a 32-bit frequency
translator (numerically controlled oscillator (NCO)), a half-
band decimating filter, a fixed FIR filter, and an fADC/8 fixed-
frequency NCO.
In addition to the receiver DDC, the AD6655 has several
functions that simplify the automatic gain control (AGC)
function in the system receiver. The fast detect feature allows
fast overrange detection by outputting four bits of input level
information with short latency.
In addition, the programmable threshold detector allows
monitoring of the incoming signal power using the four fast
detect bits of the ADC with low latency. If the input signal level
exceeds the programmable threshold, the coarse upper threshold
indicator goes high. Because this threshold indicator has low
latency, the user can quickly turn down the system gain to avoid
an overrange condition.
The second AGC-related function is the signal monitor. This
block allows the user to monitor the composite magnitude of the
incoming signal, which aids in setting the gain to optimize the
dynamic range of the overall system.
After digital processing, data can be routed directly to the two
external 14-bit output ports. These outputs can be set from 1.8 V
to 3.3 V CMOS or as 1.8 V LVDS. The CMOS data can also be
output in an interleaved configuration at a double data rate using
only Port A.
The AD6655 receiver digitizes a wide spectrum of IF frequencies.
Each receiver is designed for simultaneous reception of the main
channel and the diversity channel. This IF sampling architecture
greatly reduces component cost and complexity compared with
traditional analog techniques or less integrated digital methods.
Flexible power-down options allow significant power savings,
when desired.
Programming for setup and control is accomplished using a 3-bit
SPI-compatible serial interface.
The AD6655 is available in a 64-lead LFCSP and is specified over
the industrial temperature range of −40°C to +85°C.
Data Sheet AD6655
Rev. B | Page 5 of 84
SPECIFICATIONS
ADC DC SPECIFICATIONS—AD6655-80/AD6655-105
AVDD = 1.8 V, DVDD = 1.8 V, DRVDD = 1.8 V, maximum sample rate, VIN = −1.0 dBFS differential input, 1.0 V internal reference,
DCS enabled, unless otherwise noted.
Table 1.
Parameter
AD6655-80 AD6655-105
Unit Temperature Min Typ Max Min Typ Max
RESOLUTION
Full
14
14
Bits
ACCURACY
No Missing Codes Full Guaranteed Guaranteed
Offset Error
Full
±0.6
±0.2
±0.6
% FSR
Gain Error Full −3.6 −1.8 −0.1 −4.3 −2.2 −0.5 % FSR
MATCHING CHARACTERISTIC
Offset Error
25°C
±0.6
±0.2
±0.6
% FSR
Gain Error 25°C ±0.2 ±0.75 ±0.2 ±0.75 % FSR
TEMPERATURE DRIFT
Offset Error Full ±15 ±15 ppm/°C
Gain Error Full ±95 ±95 ppm/°C
INTERNAL VOLTAGE REFERENCE
Output Voltage Error (1 V Mode) Full ±5 ±18 ±5 ±18 mV
Load Regulation at 1.0 mA Full 7 7 mV
INPUT-REFERRED NOISE
VREF = 1.0 V 25°C 0.85 0.85 LSB rms
ANALOG INPUT
Input Span, VREF = 1.0 V
Full
2
V p-p
Input Capacitance1 Full
8
pF
VREF INPUT RESISTANCE Full 6 6 kΩ
POWER SUPPLIES
Supply Voltage
AVDD, DVDD Full
1.7
1.9
1.7
1.8
1.9
V
DRVDD (CMOS Mode)
Full
1.7
3.6
1.7
3.3
3.6
V
DRVDD (LVDS Mode) Full
1.7
1.9
1.7
1.8
1.9
V
Supply Current
IAVDD 2, 3 Full
420
315
575 mA
IDVDD2, 3 Full
225
mA
IDRVDD2 (3.3 V CMOS) Full
21
mA
IDRVDD2 (1.8 V CMOS) Full
11
mA
IDRVDD2 (1.8 V LVDS) Full
56
mA
POWER CONSUMPTION
DC Input Full
490
620
650
mW
Sine Wave Input2 (DRVDD = 1.8 V) Full
995
mW
Sine Wave Input2 (DRVDD = 3.3 V) Full
1040
mW
Standby Power4 Full
68
mW
Power-Down Power Full
8
2.5
8
mW
1 Input capacitance refers to the effective capacitance between one differential input pin and AGND. See Figure 11 for the equivalent analog input structure.
2 Measured with a 9.7 MHz, full-scale sine wave input, NCO enabled with a frequency of 13 MHz, FIR filter enabled and the fS/8 output mix enabled with approximately
5 pF loading on each output bit.
3 The maximum limit applies to the combination of IAVDD and IDVDD currents.
4 Standby power is measured with a dc input and with the CLK pin inactive (set to AVDD or AGND).
AD6655 Data Sheet
Rev. B | Page 6 of 84
ADC DC SPECIFICATIONS—AD6655-125/AD6655-150
AVDD = 1.8 V, DVDD = 1.8 V, DRVDD = 1.8 V, maximum sample rate, VIN = −1.0 dBFS differential input, 1.0 V internal reference,
DCS enabled, unless otherwise noted.
Table 2.
Parameter Temperature
AD6655-125 AD6655-150
Unit Min Typ Max Min Typ Max
RESOLUTION
Full
14
14
Bits
ACCURACY
No Missing Codes Full Guaranteed Guaranteed
Offset Error Full ±0.3 ±0.6 ±0.2 ±0.6 % FSR
Gain Error Full −4.7 −2.7 −0.8 −5.1 −3.2 −1.0 % FSR
MATCHING CHARACTERISTIC
Offset Error 25°C ±0.3 ±0.7 ±0.2 ±0.7 % FSR
Gain Error 25°C ±0.1 ±0.7 ±0.2 ±0.8 % FSR
TEMPERATURE DRIFT
Offset Error Full ±15 ±15 ppm/°C
Gain Error Full ±95 ±95 ppm/°C
INTERNAL VOLTAGE REFERENCE
Output Voltage Error (1 V Mode) Full ±5 ±18 ±5 ±18 mV
Load Regulation at 1.0 mA Full 7 7 mV
INPUT-REFERRED NOISE
VREF = 1.0 V 25°C 0.85 0.85 LSB rms
ANALOG INPUT
Input Span, VREF = 1.0 V Full 2 2 V p-p
Input Capacitance1 Full 8 8 pF
VREF INPUT RESISTANCE Full 6 6 kΩ
POWER SUPPLIES
Supply Voltage
AVDD, DVDD
Full
1.7
1.8
1.9
1.7
1.8
1.9
V
DRVDD (CMOS Mode) Full 1.7 1.8 3.6 1.7 1.8 3.6 V
DRVDD (LVDS Mode) Full 1.7 1.8 1.9 1.7 1.8 1.9 V
Supply Current
IAVDD 2, 3 Full 390 705 440 805 mA
IDVDD2, 3 Full 270 320 mA
IDRVDD2 (3.3 V CMOS) Full 26 28 mA
IDRVDD2 (1.8 V CMOS) Full 13 17 mA
IDRVDD2 (1.8 V LVDS) Full 57 57 mA
POWER CONSUMPTION
DC Input Full 770 810 870 920 mW
Sine Wave Input2 (DRVDD = 1.8 V) Full 1215 1395 mW
Sine Wave Input2 (DRVDD = 3.3 V) Full 1275 1450 mW
Standby Power4 Full 77 77 mW
Power-down Power
Full
2.5
8
2.5
8
mW
1 Input capacitance refers to the effective capacitance between one differential input pin and AGND. See Figure 11 for the equivalent analog input structure.
2 Measured with a 9.7 MHz, full-scale sine wave input, NCO enabled with a frequency of 13 MHz, FIR filter enabled and the fS/8 output mix enabled with approximately
5 pF loading on each output bit.
3 The maximum limit applies to the combination of IAVDD and IDVDD currents.
4 Standby power is measured with a dc input, the CLK pin inactive (set to AVDD or AGND).
Data Sheet AD6655
Rev. B | Page 7 of 84
ADC AC SPECIFICATIONS—AD6655-80/AD6655-105
AVDD = 1.8 V, DVDD = 1.8 V, DRVDD = 1.8 V, maximum sample rate, VIN = −1.0 dBFS differential input, 1.0 V internal reference,
DCS enabled, NCO enabled, half-band filter enabled, FIR filter enabled, unless otherwise noted.
Table 3.
Parameter1 Temperature
AD6655-80 AD6655-105
Unit Min Typ Max Min Typ Max
SIGNAL-TO-NOISE-RATIO (SNR)
fIN = 2.4 MHz 25°C 74.9 74.8 dB
fIN = 70 MHz 25°C 74.8 74.7 dB
Full 73.0 73.0 dB
fIN = 140 MHz 25°C 74.5 74.3 dB
fIN = 220 MHz 25°C
73.4
73.4
dB
WORST SECOND OR THIRD HARMONIC
fIN = 2.4 MHz
25°C
−86
−86
dBc
fIN = 70 MHz
25°C
−85
−85
dBc
Full
−74
−74
dBc
fIN = 140 MHz
25°C
−84
−84
dBc
f
IN
= 220 MHz
25°C
−83
−83
dBc
SPURIOUS-FREE DYNAMIC RANGE
(SFDR)
f
IN
= 2.4 MHz
25°C
86
86
dBc
fIN = 70 MHz
25°C
85
85
dBc
Full
74
74
dBc
fIN = 140 MHz
25°C
84
84
dBc
fIN = 220 MHz
25°C
83
83
dBc
WORST OTHER HARMONIC OR SPUR2
fIN = 2.4 MHz
25°C
−93
−93
dBc
fIN = 70 MHz
25°C
−90 −90
dBc
Full
−82
−82
dBc
fIN = 140 MHz
25°C
−89
−89
dBc
fIN = 220 MHz
25°C
−86
−86
dBc
TWO-TONE SFDR
fIN = 29.12 MHz, 32.12 MHz (−7 dBFS)
25°C
85
85
dBc
fIN = 169.12 MHz, 172.12 MHz (−7 dBFS)
25°C
81
81
dBc
CROSSTALK3
Full
95
95
dB
ANALOG INPUT BANDWIDTH
25°C
650
650
MHz
1 See Application Note AN-835, Understanding High Speed ADC Testing and Evaluation, for a complete set of definitions.
2 See the Applications Information section for more information about the worst other specifications for the AD6655.
3 Crosstalk is measured at 100 MHz with −1 dBFS on one channel and with no input on the alternate channel.
AD6655 Data Sheet
Rev. B | Page 8 of 84
ADC AC SPECIFICATIONS—AD6655-125/AD6655-150
AVDD = 1.8 V, DVDD = 1.8 V, DRVDD = 1.8 V, maximum sample rate, VIN = −1.0 dBFS differential input, 1.0 V internal reference,
DCS enabled, NCO enabled, half-band filter enabled, FIR filter enabled, unless otherwise noted.
Table 4.
Parameter1 Temperature
AD6655-125 AD6655-150
Unit Min Typ Max Min Typ Max
SIGNAL-TO-NOISE-RATIO (SNR)
fIN = 2.4 MHz 25°C 74.7 74.6 dB
fIN = 70 MHz 25°C 74.6 74.5 dB
Full 73.0
72.5
dB
fIN = 140 MHz 25°C 74.2 73.9 dB
fIN = 220 MHz 25°C
73.3
73.0
dB
WORST SECOND OR THIRD HARMONIC
fIN = 2.4 MHz
25°C
−86
−85
dBc
fIN = 70 MHz
25°C
−85
−84
dBc
Full
−73
−73
dBc
fIN = 140 MHz
25°C
−84
−83
dBc
f
IN
= 220 MHz
25°C
−83
−77
dBc
SPURIOUS-FREE DYNAMIC RANGE (SFDR)
fIN = 2.4 MHz
25°C
86
85
dBc
fIN = 70 MHz
25°C
85
80
dBc
Full
73
73
dBc
fIN = 140 MHz
25°C
84
76
dBc
fIN = 220 MHz
25°C
83
74
dBc
WORST OTHER HARMONIC OR SPUR2
fIN = 2.4 MHz
25°C
−92
−87
dBc
fIN = 70 MHz
25°C
−90
−80
dBc
Full
−82 −80
dBc
f
IN
= 140 MHz
25°C
−88
−76
dBc
fIN = 220 MHz
25°C
−84
−74
dBc
TWO-TONE SFDR
f
IN
= 29.12 MHz, 32.12 MHz (−7 dBFS)
25°C
85
85
dBc
fIN = 169.12 MHz, 172.12 MHz (−7 dBFS)
25°C
81
81
dBc
CROSSTALK3
Full
95
95
dB
ANALOG INPUT BANDWIDTH
25°C
650
650
MHz
1 See Application Note AN-835, Understanding High Speed ADC Testing and Evaluation, for a complete set of definitions.
2 See the Applications Information section for more information about the worst other specifications for the AD6655.
3 Crosstalk is measured at 100 MHz with −1 dBFS on one channel and with no input on the alternate channel.
Data Sheet AD6655
Rev. B | Page 9 of 84
DIGITAL SPECIFICATIONS—AD6655-80/AD6655-105
AVDD = 1.8 V, DVDD = 1.8 V, DRVDD = 1.8 V, maximum sample rate, VIN = −1.0 dBFS differential input, 1.0 V internal reference,
DCS enabled, unless otherwise noted.
Table 5.
Parameter Temp
AD6655-80 AD6655-105
Unit Min Typ Max Min Typ Max
DIFFERENTIAL CLOCK INPUTS (CLK+, CLK−)
Logic Compliance CMOS/LVDS/LVPECL CMOS/LVDS/LVPECL
Internal Common-Mode Bias Full 1.2 1.2 V
Differential Input Voltage
Full
0.2
6
0.2
6
V p-p
Input Voltage Range
Full
AVDD
−
0.3
AVDD + 1.6
AVDD − 0.3
AVDD + 1.6
V
Input Common-Mode Range
Full
1.1
AVDD
1.1
AVDD
V
High Level Input Voltage Full 1.2 3.6 1.2 3.6 V
Low Level Input Voltage Full
0
0.8
0
0.8
V
High Level Input Current
Full
−10
+10
−10
+10
µA
Low Level Input Current Full
−10
+10
−10
+10
µA
Input Capacitance
Full
4
4
pF
Input Resistance
Full
8
10
12
8
10
12
kΩ
SYNC INPUT
Logic Compliance CMOS CMOS
Internal Bias Full 1.2 1.2 V
Input Voltage Range Full AVDD − 0.3 AVDD + 1.6 AVDD − 0.3 AVDD + 1.6 V
High Level Input Voltage Full 1.2 3.6 1.2 3.6 V
Low Level Input Voltage Full 0 0.8 0 0.8 V
High Level Input Current Full −10 +10 −10 +10 µA
Low Level Input Current Full −10 +10 −10 +10 µA
Input Capacitance Full 4 4 pF
Input Resistance Full 8 10 12 8 10 12 kΩ
LOGIC INPUT (CSB)1
High Level Input Voltage Full 1.22 3.6 1.22 3.6 V
Low Level Input Voltage Full
0
0.6
0
0.6
V
High Level Input Current
Full
−10
+10
−10
+10
µA
Low Level Input Current Full
40
132
40
132
µA
Input Resistance Full
26
26
kΩ
Input Capacitance Full
2
2
pF
LOGIC INPUT (SCLK/DFS)2
High Level Input Voltage Full 1.22 3.6 1.22 3.6 V
Low Level Input Voltage Full
0
0.6
0
0.6
V
High Level Input Current Full
−92
−135
−92
−135
µA
Low Level Input Current
Full
−10
+10
−10
+10
µA
Input Resistance Full
26
26
kΩ
Input Capacitance Full
2
2
pF
LOGIC INPUTS (SDIO/DCS, SMI SDFS)
1
High Level Input Voltage Full
1.22
3.6
1.22
3.6
V
Low Level Input Voltage Full
0
0.6
0
0.6
V
High Level Input Current Full
−10
+10
−10
+10
µA
Low Level Input Current Full
38
128
38
128
µA
Input Resistance Full
26
26
kΩ
Input Capacitance Full
5
5
pF
AD6655 Data Sheet
Rev. B | Page 10 of 84
Parameter Temp
AD6655-80 AD6655-105
Unit Min Typ Max Min Typ Max
LOGIC INPUTS (SMI SDO/OEB,
SMI SCLK/PDWN)2
High Level Input Voltage Full
1.22
3.6
1.22
3.6
V
Low Level Input Voltage Full
0
0.6
0
0.6
V
High Level Input Current Full
−90
−134
−90
−134
µA
Low Level Input Current Full
−10
+10
−10
+10
µA
Input Resistance Full
26
26
kΩ
Input Capacitance Full
5
5
pF
DIGITAL OUTPUTS
CMOS Mode—DRVDD = 3.3 V
High Level Output Voltage
I
OH
= 50 µA
Full
3.29
3.29
V
IOH = 0.5 mA Full
3.25
3.25
V
Low Level Output Voltage
IOL = 1.6 mA Full
0.2
0.2
V
IOL = 50 µA Full
0.05
0.05
V
CMOS Mode—DRVDD = 1.8 V
High Level Output Voltage
IOH = 50 µA Full
1.79
1.79
V
IOH = 0.5 mA Full
1.75
1.75
V
Low Level Output Voltage
IOL = 1.6 mA Full
0.2
0.2
V
I
OL
= 50 µA
Full
0.05
0.05
V
LVDS Mode, DRVDD = 1.8 V
Differential Output Voltage (VOD),
ANSI Mode
Full
250
350
450
250
350
450
mV
Output Offset Voltage (VOS),
ANSI Mode
Full
1.15
1.25
1.35
1.15
1.25
1.35
V
Differential Output Voltage (VOD),
Reduced Swing Mode
Full
150
200
280
150
200
280
mV
Output Offset Voltage (VOS),
Reduced Swing Mode
Full
1.15
1.25
1.35
1.15
1.25
1.35
V
1 Pull up.
2 Pull down.
Data Sheet AD6655
Rev. B | Page 11 of 84
DIGITAL SPECIFICATIONS—AD6655-125/AD6655-150
AVDD = 1.8 V, DVDD = 1.8 V, DRVDD = 1.8 V, maximum sample rate, VIN = −1.0 dBFS differential input, 1.0 V internal reference,
DCS enabled, unless otherwise noted.
Table 6.
Parameter
Temp
AD6655-125 AD6655-150
Unit Min Typ Max Min Typ Max
DIFFERENTIAL CLOCK INPUTS (CLK+, CLK−)
Logic Compliance CMOS/LVDS/LVPECL CMOS/LVDS/LVPECL
Internal Common-Mode Bias Full 1.2 1.2 V
Differential Input Voltage
Full
0.2
6
0.2
6
V p-p
Input Voltage Range
Full
AVDD − 0.3
AVDD + 1.6
AVDD − 0.3
AVDD + 1.6
V
Input Common-Mode Range
Full
1.1 V
AVDD
1.1 V
AVDD
V
High Level Input Voltage Full 1.2 3.6 1.2 3.6 V
Low Level Input Voltage Full 0 0.8 0 0.8 V
High Level Input Current
Full
−10
+10
−10
+10
µA
Low Level Input Current Full −10 +10 −10 +10 µA
Input Capacitance
Full
4
4
pF
Input Resistance
Full
8
10
12
8
10
12
kΩ
SYNC INPUT
Logic Compliance CMOS CMOS
Internal Bias Full 1.2 1.2 V
Input Voltage Range Full AVDD − 0.3 AVDD + 1.6 AVDD − 0.3 AVDD + 1.6 V
High Level Input Voltage Full 1.2 3.6 1.2 3.6 V
Low Level Input Voltage Full 0 0.8 0 0.8 V
High Level Input Current Full −10 +10 −10 +10 µA
Low Level Input Current Full −10 +10 −10 +10 µA
Input Capacitance Full 4 4 pF
Input Resistance Full 8 10 12 8 10 12 kΩ
LOGIC INPUT (CSB)1
High Level Input Voltage Full 1.22 3.6 1.22 3.6 V
Low Level Input Voltage Full 0 0.6 0 0.6 V
High Level Input Current
Full
−10
+10
−10
+10
µA
Low Level Input Current Full 40 132 40 132 µA
Input Resistance Full 26 26 kΩ
Input Capacitance Full 2 2 pF
LOGIC INPUT (SCLK/DFS)2
High Level Input Voltage Full 1.22 3.6 1.22 3.6 V
Low Level Input Voltage Full 0 0.6 0 0.6 V
High Level Input Current Full −92 −135 −92 −135 µA
Low Level Input Current
Full
−10
+10
−10
+10
µA
Input Resistance Full 26 26 kΩ
Input Capacitance Full 2 2 pF
LOGIC INPUTS (SDIO/DCS, SMI SDFS)
1
High Level Input Voltage Full 1.22 3.6 1.22 3.6 V
Low Level Input Voltage Full 0 0.6 0 0.6 V
High Level Input Current Full −10 +10 −10 +10 µA
Low Level Input Current Full 38 128 38 128 µA
Input Resistance Full 26 26 kΩ
Input Capacitance Full 5 5 pF
AD6655 Data Sheet
Rev. B | Page 12 of 84
Parameter
Temp
AD6655-125 AD6655-150
Unit Min Typ Max Min Typ Max
LOGIC INPUTS (SMI SDO/OEB,
SMI SCLK/PDWN)2
High Level Input Voltage Full 1.22 3.6 1.22 3.6 V
Low Level Input Voltage Full 0 0.6 0 0.6 V
High Level Input Current Full −90 −134 −90 −134 µA
Low Level Input Current Full −10 +10 −10 +10 µA
Input Resistance Full 26 26 kΩ
Input Capacitance Full 5 5 pF
DIGITAL OUTPUTS
CMOS Mode—DRVDD = 3.3 V
High Level Output Voltage
I
OH
= 50 µA
Full
3.29
3.29
V
IOH = 0.5 mA Full 3.25 3.25 V
Low Level Output Voltage
IOL = 1.6 mA Full 0.2 0.2 V
IOL = 50 µA Full 0.05 0.05 V
CMOS Mode—DRVDD = 1.8 V
High Level Output Voltage
IOH = 50 µA Full 1.79 1.79 V
IOH = 0.5 mA Full 1.75 1.75 V
Low Level Output Voltage
IOL = 1.6 mA Full 0.2 0.2 V
I
OL
= 50 µA
Full
0.05
0.05
V
LVDS Mode—DRVDD = 1.8 V
Differential Output Voltage (VOD),
ANSI Mode
Full 250 350 450 250 350 450 mV
Output Offset Voltage (VOS),
ANSI Mode
Full 1.15 1.25 1.35 1.15 1.25 1.35 V
Differential Output Voltage (VOD),
Reduced Swing Mode
Full
150
200
280
150
200
280
mV
Output Offset Voltage (VOS),
Reduced Swing Mode
Full 1.15 1.25 1.35 1.15 1.25 1.35 V
1 Pull up.
2 Pull down.
Data Sheet AD6655
Rev. B | Page 13 of 84
SWITCHING SPECIFICATIONS—AD6655-80/AD6655-105
Table 7.
Parameter Temp
AD6655-80 AD6655-105
Unit Min Typ Max Min Typ Max
CLOCK INPUT PARAMETERS
Input Clock Rate Full 625 625 MHz
Conversion Rate1
DCS Enabled Full 20 80 20 105 MSPS
DCS Disabled
Full
10
80
10
105
MSPS
CLK Period—Divide-by-1 Mode (tCLK) Full 12.5 9.5 ns
CLK Pulse Width High (tCLKH)
Divide-by-1 Mode, DCS Enabled Full 3.75 6.25 8.75 2.85 4.75 6.65 ns
Divide-by-1 Mode DCS Disabled Full 5.63 6.25 6.88 4.28 4.75 5.23 ns
Divide-by-2 Mode, DCS Enabled Full 1.6 1.6 ns
Divide-by-3 Through Divide-by-8 Modes, DCS Enabled Full 0.8 0.8 ns
DATA OUTPUT PARAMETERS (DATA, FD)
CMOS Noninterleaved Mode—DRVDD = 1.8 V
Data Propagation Delay (tPD)2 Full 1.6 3.9 6.2 1.6 3.9 6.2 ns
DCO Propagation Delay (tDCO) Full 4.0 5.4 7.3 4.0 5.4 7.3 ns
Setup Time (tS) Full 14.0 11.0 ns
Hold Time (tH) Full 11.0 8.0 ns
CMOS Noninterleaved Mode—DRVDD = 3.3 V
Data Propagation Delay (t
PD
)2
Full
1.9
4.1
6.4
1.9
4.1
6.4
ns
DCO Propagation Delay (tDCO) Full 4.4 5.8 7.7 4.4 5.8 7.7 ns
Setup Time (tS) Full 14.2 11.2 ns
Hold Time (tH) Full 10.8 7.8 ns
CMOS Interleaved and IQ Mode—DRVDD = 1.8 V
Data Propagation Delay (tPD)2 Full 1.6 3.9 6.2 1.6 3.9 6.2 ns
DCO Propagation Delay (tDCO) Full 3.4 4.8 6.7 3.4 4.8 6.7 ns
Setup Time (tS) Full 7.15 5.65 ns
Hold Time (tH) Full 5.35 3.85 ns
CMOS Interleaved and IQ Mode—DRVDD = 3.3 V
Data Propagation Delay (tPD)2 Full 1.9 4.1 6.4 1.9 4.1 6.4 ns
DCO Propagation Delay (t
DCO
)
Full
3.8
5.2
7.1
3.8
5.2
7.1
ns
Setup Time (tS) Full 7.35 5.85 ns
Hold Time (tH) Full 5.15 3.65 ns
LVDS Mode—DRVDD = 1.8 V
Data Propagation Delay (tPD)2 Full 2.5 4.8 7.0 2.5 4.8 7.0 ns
DCO Propagation Delay (tDCO) Full 3.7 5.3 7.3 3.7 5.3 7.3 ns
Pipeline Delay (Latency) NCO, FIR, f
S
/8 Mix Disabled
Full
38
38
Cycles
Pipeline Delay (Latency) NCO Enabled, FIR and fS/8 Mix Disabled
(Complex Output Mode)
Full 38 38 Cycles
Pipeline Delay (Latency) NCO, FIR, and fS/8 Mix Enabled Full 109 109 Cycles
Aperture Delay (tA) Full 1.0 1.0 ns
Aperture Uncertainty (Jitter, t
J
)
Full
0.1
0.1
ps rms
Wake-Up Time3 Full 350 350 us
OUT-OF-RANGE RECOVERY TIME Full 2 2 Cycles
1 Conversion rate is the clock rate after the divider.
2 Output propagation delay is measured from CLK 50% transition to DATA 50% transition, with a 5 pF load.
3 Wake-up time is dependent on the value of the decoupling capacitors.
AD6655 Data Sheet
Rev. B | Page 14 of 84
SWITCHING SPECIFICATIONS—AD6655-125/AD6655-150
Table 8.
Parameter Temp
AD6655-125 AD6655-150
Unit Min Typ Max Min Typ Max
CLOCK INPUT PARAMETERS
Input Clock Rate Full 625 625 MHz
Conversion Rate1
DCS Enabled Full 20 125 20 150 MSPS
DCS Disabled
Full
10
125
10
150
MSPS
CLK Period—Divide-by-1 Mode (tCLK) Full 8 6.66 ns
CLK Pulse Width High (tCLKH)
Divide-by-1 Mode, DCS Enabled Full 2.4 4 5.6 2.0 3.33 4.66 ns
Divide-by-1 Mode, DCS Disabled Full 3.6 4 4.4 3.0 3.33 3.66 ns
Divide-by-2 Mode, DCS Enabled Full 1.6 1.6 ns
Divide-by-3 Through Divide-by-8 Modes, DCS Enabled Full 0.8 0.8 ns
DATA OUTPUT PARAMETERS (DATA, FD)
CMOS Noninterleaved Mode—DRVDD = 1.8 V
Data Propagation Delay (tPD)2 Full 1.6 3.9 6.2 1.6 3.9 6.2 ns
DCO Propagation Delay (tDCO) Full 4.0 5.4 7.3 4.0 5.4 7.3 ns
Setup Time (tS) Full 9.5 8.16 ns
Hold Time (tH) Full 6.5 5.16 ns
CMOS Noninterleaved Mode—DRVDD = 3.3 V
Data Propagation Delay (t
PD
)2
Full
1.9
4.1
6.4
1.9
4.1
6.4
ns
DCO Propagation Delay (tDCO) Full 4.4 5.8 7.7 4.4 5.8 7.7 ns
Setup Time (tS) Full 9.7 8.36 ns
Hold Time (tH) Full 6.3 4.96 ns
CMOS Interleaved and IQ Mode—DRVDD = 1.8 V
Data Propagation Delay (tPD)2 Full 1.6 3.9 6.2 1.6 3.9 6.2 ns
DCO Propagation Delay (tDCO) Full 3.4 4.8 6.7 3.4 4.8 6.7 ns
Setup Time (tS) Full 4.9 4.23 ns
Hold Time (tH) Full 3.1 2.43 ns
CMOS Interleaved and IQ Mode—DRVDD = 3.3 V
Data Propagation Delay (tPD)2 Full 1.9 4.1 6.4 1.9 4.1 6.4 ns
DCO Propagation Delay (t
DCO
)
Full
3.8
5.2
7.1
3.8
5.2
7.1
ns
Setup Time (tS) Full 5.1 4.43 ns
Hold Time (tH) Full 2.9 2.23 ns
LVDS Mode—DRVDD = 1.8 V
Data Propagation Delay (tPD)2 Full 2.5 4.8 7.0 2.5 4.8 7.0 ns
DCO Propagation Delay (tDCO) Full 3.7 5.3 7.3 3.7 5.3 7.3 ns
Pipeline Delay (Latency) NCO, FIR, f
S
/8 Mix Disabled
Full
38
38
Cycles
Pipeline Delay (Latency) NCO Enabled; FIR and fS/8 Mix Disabled
(Complex Output Mode)
Full 38 38 Cycles
Pipeline Delay (Latency) NCO, FIR, and fS/8 Mix Enabled Full 109 109 Cycles
Aperture Delay (tA) Full 1.0 1.0 ns
Aperture Uncertainty (Jitter, t
J
)
Full
0.1
0.1
ps rms
Wake-Up Time3 Full 350 350 us
OUT-OF-RANGE RECOVERY TIME Full 3 3 Cycles
1 Conversion rate is the clock rate after the divider.
2 Output propagation delay is measured from CLK 50% transition to DATA 50% transition, with a 5 pF load.
3 Wake-up time is dependent on the value of the decoupling capacitors.
Data Sheet AD6655
Rev. B | Page 15 of 84
TIMING SPECIFICATIONS
Table 9.
Parameter Conditions Min Typ Max Unit
SYNC TIMING REQUIREMENTS
tSSYNC SYNC to the rising edge of CLK setup time 0.24 ns
tHSYNC SYNC to the rising edge of CLK hold time 0.4 ns
SPI TIMING REQUIREMENTS
t
DS
Setup time between the data and the rising edge of SCLK
2
ns
tDH Hold time between the data and the rising edge of SCLK 2 ns
tCLK Period of the SCLK 40 ns
tS Setup time between CSB and SCLK 2 ns
tH Hold time between CSB and SCLK 2 ns
tHIGH Minimum period that SCLK should be in a logic high state 10 ns
tLOW Minimum period that SCLK should be in a logic low state 10 ns
tEN_SDIO Time required for the SDIO pin to switch from an input to an output
relative to the SCLK falling edge
10 ns
tDIS_SDIO Time required for the SDIO pin to switch from an output to an input
relative to the SCLK rising edge
10 ns
SPORT TIMING REQUIREMENTS
tCSSCLK Delay from rising edge of CLK+ to rising edge of SMI SCLK 3.2 4.5 6.2 ns
tSSLKSDO Delay from rising edge of SMI SCLK to SMI SDO −0.4 0 +0.4 ns
t
SSCLKSDFS
Delay from rising edge of SMI SCLK to SMI SDFS
−0.4
0
+0.4
ns
Timing Diagrams
06709-109
t
H
t
S
CLK+
DECIMATED
CMO S DATA
DECIMATED
FD DATA CHANNEL A/B
FD BITS CHANNE L A/ B
FD BITS CHANNE L A/ B
FD BITS
CHANNEL A/B
DATA BITS CHANNEL A/B
DATA BITS CHANNEL A/B
DATA BITS
CHANNEL A/B
FD BITS CHANNEL A/B
FD BITS CHANNEL A/ B
FD BITS
DECIMATED
DCOA/DCOB
t
PD
t
DCO
Figure 2. Decimated Noninterleaved CMOS Mode Data and Fast Detect Output Timing (Fast Detect Mode Select Bits = 000)
t
S
t
PD
t
DCO
t
H
CLK+
DECIMATED
CMO S DATA CHANNEL A/B
DATA BITS CHANNEL A/B
DATA BITS
DECIMATED
FD DATA CHANNEL A/B
FD BITS CHANNEL A/B
FD BITS
DECIMATED
DCOA/DCOB
CHANNEL A/B
DATA BITS
CHANNEL A/B
FD BITS
06709-012
Figure 3. Decimated Noninterleaved CMOS Mode Data and Fast Detect Output Timing (Fast Detect Mode Select Bits = 001 Through Fast Detect Mode Select Bits = 100)
AD6655 Data Sheet
Rev. B | Page 16 of 84
t
PD
t
DCO
t
H
t
S
CLK+
DECIMATED
INTERLEAVED
CMO S DATA
CHANNEL B:
DATA CHANNE L A:
DATA CHANNE L B:
DATA CHANNE L B:
DATA
CHANNEL A:
DATA
CHANNEL B:
FD BITS CHANNEL A:
FD BITS CHANNEL B:
FD BITS CHANNEL B:
FD BITS
CHANNEL A:
FD BITS
DECIMATED
INTERLEAVED
FD DATA
DECIMATED
DCO
CHANNEL A:
DATA
CHANNEL A:
FD BITS
06709-013
Figure 4. Decimated Interleaved CMOS Mode Data and Fast Detect Output Timing
tPD tDCO
tH
tS
CLK+
DECIMATED
CMOS IQ
OUTPUT DATA
CHANNEL A/B:
I DATA CHANNE L A/B:
Q DATA CHANNEL A/B:
Q DATA CHANNEL A/B:
I DATA
CHANNEL A/B:
Q DATA
CHANNEL A/B:
FD BITS CHANNEL A/ B:
FD BITS CHANNEL A/B:
FD BITS CHANNEL A/ B:
FD BITS
CHANNEL A/B:
FD BITS
CMOS FD
DATA
DECIMATED
DCOA/DCOB
CHANNEL A/B:
I DATA
CHANNEL A/B:
FD BITS
06709-014
Figure 5. Decimated IQ Mode CMOS Data and Fast Detect Output Timing
t
PD
t
DCO
CLK–
CLK+
LVDS
DATA CHANNE L A:
DATA CHANNE L B:
DATA CHANNE L A:
DATA
LVDS
FAS T DET
DCO–
DCO+
CHANNEL B:
DATA
CHANNEL A:
FD CHANNEL B:
FD CHANNEL A:
FD
CHANNEL B:
FD
CHANNEL A:
DATA
CHANNEL A:
FD
06709-015
Figure 6. Decimated Interleaved LVDS Mode Data and Fast Detect Output Timing
tSSYNC tHSYNC
SYNC
CLK+
06709-016
Figure 7. SYNC Timing Inputs
Data Sheet AD6655
Rev. B | Page 17 of 84
t
CSSCLK
t
SSCLKSDFS
t
SSCLKSDFS
CLK+
CLK–
SMI SCLK
SMI SDFS
SMI SDO DATA DATA
06709-017
Figure 8. Signal Monitor SPORT Output Timing
AD6655 Data Sheet
Rev. B | Page 18 of 84
ABSOLUTE MAXIMUM RATINGS
Table 10.
Parameter Rating
ELECTRICAL
AVDD, DVDD to AGND −0.3 V to +2.0 V
DRVDD to DRGND −0.3 V to +3.9 V
AGND to DRGND −0.3 V to +0.3 V
VIN+A/VIN+B, VIN-A/VIN−B to AGND
−0.3 V to AVDD + 0.2 V
CLK+, CLK− to AGND −0.3 V to +3.9 V
SYNC to AGND −0.3 V to +3.9 V
VREF to AGND −0.3 V to AVDD + 0.2 V
SENSE to AGND −0.3 V to AVDD + 0.2 V
CML to AGND −0.3 V to AVDD + 0.2 V
RBIAS to AGND
−0.3 V to AVDD + 0.2 V
CSB to AGND −0.3 V to +3.9 V
SCLK/DFS to DRGND −0.3 V to +3.9 V
SDIO/DCS to DRGND −0.3 V to DRVDD + 0.3 V
SMI SDO/OEB to DRGND −0.3 V to DRVDD + 0.3 V
SMI SCLK/PDWN to DRGND −0.3 V to DRVDD + 0.3 V
SMI SDFS to DRGND −0.3 V to DRVDD + 0.3 V
D0A/D0B through D13A/D13B
to DRGND
−0.3 V to DRVDD + 0.3 V
FD0A/FD0B through FD3A/FD3B to
DRGND
−0.3 V to DRVDD + 0.3 V
DCOA/DCOB to DRGND
−0.3 V to DRVDD + 0.3 V
ENVIRONMENTAL
Operating Temperature Range
(Ambient)
−40°C to +85°C
Maximum Junction Temperature
Under Bias
150°C
Storage Temperature Range
(Ambient)
−65°C to +125°C
Stresses above those listed under Absolute Maximum Ratings
may cause permanent damage to the device. This is a stress
rating only; functional operation of the device at these or any
other conditions above those indicated in the operational
section of this specification is not implied. Exposure to absolute
maximum rating conditions for extended periods may affect
device reliability.
THERMAL CHARACTERISTICS
The exposed paddle must be soldered to the ground plane for
the LFCSP package. Soldering the exposed paddle to the
customer board increases the reliability of the solder joints,
maximizing the thermal capability of the package.
Table 11. Thermal Resistance
Package
Type
Airflow
Velocity
(m/s) θJA1, 2 θJC1, 3 θJB1, 4 Unit
64-Lead LFCSP
9 mm × 9 mm
(CP-64-6)
0 18.8 0.6 6.0 °C/W
1.0 16.5 °C/W
2.0
15.8
°C/W
1 Per JEDEC 51-7, plus JEDEC 25-5 2S2P test board.
2 Per JEDEC JESD51-2 (still air) or JEDEC JESD51-6 (moving air).
3 Per MIL-Std 883, Method 1012.1.
4 Per JEDEC JESD51-8 (still air).
Typical θJA is specified for a 4-layer PCB with solid ground
plane. As shown, airflow increases heat dissipation, which
reduces θJA. In addition, metal in direct contact with the
package leads from metal traces, through holes, ground, and
power planes, reduces the θJA.
ESD CAUTION
Data Sheet AD6655
Rev. B | Page 19 of 84
PIN CONFIGURATIONS AND FUNCTION DESCRIPTIONS
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
D5A
D6A
D7A
DRGND
DRVDD
D8A
D9A
DVDD
D10A
D11A
D12A
D13A (MS B)
FD0A
FD1A
FD2A
FD3A
64
63
62
61
60
59
58
57
56
55
54
53
52
51
50
49
DRGND
D5B
D4B
D3B
D2B
D1B
D0B (L S B)
DVDD
FD3B
FD2B
FD1B
FD0B
SYNC
CSB
CLK–
CLK+
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
DRVDD
D6B
D7B
D8B
D9B
D10B
D11B
D12B
D13B (MS B)
DCOB
DCOA
D0A (L S B)
D1A
D2A
D3A
D4A
SCLK/DFS
SDIO/DCS
AVDD
AVDD
VIN+B
VIN–B
RBIAS
CML
SENSE
VREF
VIN–A
VIN+A
AVDD
SMI SDFS
SMI SCLK/PDWN
SMI SDO/O EB
48
47
46
45
44
43
42
41
40
39
38
37
36
35
34
33
PIN 1
INDICATOR
AD6655
PARAL LEL CM OS
TOP VI EW
(No t t o Scal e)
EXPOSED PADDLE, PI N 0
(BOTTOM OF PACKAGE)
06709-002
NOTES
1. THE EXPOSED THERMALPAD ON T HE BOTTOM OF THEPACKAGE P ROVIDES THE
ANALOG GRO UND FO R THE PART. T HIS EXPO SED PAD MUS T BE CONNECTED TO
GROUND FOR PROPE R OPE RATION.
Figure 9. LFCSP Parallel CMOS Pin Configuration (Top View)
Table 12. Pin Function Descriptions (Parallel CMOS Mode)
Pin No. Mnemonic Type Description
ADC Power Supplies
20, 64 DRGND Ground Digital Output Ground.
1, 21 DRVDD Supply Digital Output Driver Supply (1.8 V to 3.3 V).
24, 57 DVDD Supply Digital Power Supply (1.8 V Nominal).
36, 45, 46
AVDD
Supply
Analog Power Supply (1.8 V Nominal).
0 AGND,
Exposed Pad
Ground Analog Ground. The exposed thermal pad on the bottom of the package provides the
analog ground for the part. This pad must be connected to ground for proper operation.
ADC Analog
37 VIN+A Input Differential Analog Input Pin (+) for Channel A.
38 VIN−A Input Differential Analog Input Pin (−) for Channel A.
44 VIN+B Input Differential Analog Input Pin (+) for Channel B.
43 VIN−B Input Differential Analog Input Pin (−) for Channel B.
39 VREF Input/Output Voltage Reference Input/Output.
40
SENSE
Input
Voltage Reference Mode Select. (See Table 15 for details.)
42 RBIAS Input/Output External Reference Bias Resistor.
41 CML Output Common-Mode Level Bias Output for Analog Inputs.
49 CLK+ Input ADC Clock Input—True.
50 CLK− Input ADC Clock Input—Complement.
ADC Fast Detect Outputs
29 FD0A Output Channel A Fast Detect Indicator. (See Table 21 for details.)
30
FD1A
Output
Channel A Fast Detect Indicator. (See Table 21 for details.)
31 FD2A Output Channel A Fast Detect Indicator. (See Table 21 for details.)
32 FD3A Output Channel A Fast Detect Indicator. (See Table 21 for details.)
53 FD0B Output Channel B Fast Detect Indicator. (See Table 21 for details.)
54 FD1B Output Channel B Fast Detect Indicator. (See Table 21 for details.)
55 FD2B Output Channel B Fast Detect Indicator. (See Table 21 for details.)
56
FD3B
Output
Channel B Fast Detect Indicator. (See Table 21 for details.)
AD6655 Data Sheet
Rev. B | Page 20 of 84
Pin No. Mnemonic Type Description
Digital Input
52 SYNC Input Digital Synchronization Pin. Slave mode only.
Digital Outputs
12 D0A (LSB) Output Channel A CMOS Output Data.
13 D1A Output Channel A CMOS Output Data.
14 D2A Output Channel A CMOS Output Data.
15 D3A Output Channel A CMOS Output Data.
16 D4A Output Channel A CMOS Output Data.
17 D5A Output Channel A CMOS Output Data.
18 D6A Output Channel A CMOS Output Data.
19
D7A
Output
Channel A CMOS Output Data.
22 D8A Output Channel A CMOS Output Data.
23 D9A Output Channel A CMOS Output Data.
25 D10A Output Channel A CMOS Output Data.
26 D11A Output Channel A CMOS Output Data.
27 D12A Output Channel A CMOS Output Data.
28 D13A (MSB) Output Channel A CMOS Output Data.
58 D0B (LSB) Output Channel B CMOS Output Data.
59 D1B Output Channel B CMOS Output Data.
60 D2B Output Channel B CMOS Output Data.
61 D3B Output Channel B CMOS Output Data.
62
D4B
Output
Channel B CMOS Output Data.
63 D5B Output Channel B CMOS Output Data.
2 D6B Output Channel B CMOS Output Data.
3 D7B Output Channel B CMOS Output Data.
4 D8B Output Channel B CMOS Output Data.
5 D9B Output Channel B CMOS Output Data.
6
D10B
Output
Channel B CMOS Output Data.
7 D11B Output Channel B CMOS Output Data.
8 D12B Output Channel B CMOS Output Data.
9 D13B (MSB) Output Channel B CMOS Output Data.
11 DCOA Output Channel A Data Clock Output.
10
DCOB
Output
Channel B Data Clock Output.
SPI Control
48
SCLK/DFS
Input
SPI Serial Clock/Data Format Select Pin in External Pin Mode.
47
SDIO/DCS
Input/Output
SPI Serial Data I/O/Duty Cycle Stabilizer Pin in External Pin Mode.
51 CSB Input SPI Chip Select. Active low.
Signal Monitor Port
33 SMI SDO/OEB Input/Output Signal Monitor Serial Data Output/Output Enable Input (Active Low) in External Pin Mode.
35 SMI SDFS
Output Signal Monitor Serial Data Frame Sync.
34
SMI SCLK/PDWN
Input/Output
Signal Monitor Serial Clock Output/Power-Down Input (Active High) in External Pin Mode.
Data Sheet AD6655
Rev. B | Page 21 of 84
PIN 1
INDICATOR
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
D7+
D8–
D8+
DRGND
DRVDD
D9–
D9+
DVDD
D10–
D10+
D11–
D11+
D12–
D12+
D13– (MS B)
D13+ (MS B)
64
63
62
61
60
59
58
57
56
55
54
53
52
51
50
49
DRGND
D0+ (L S B)
D0– (L S B)
FD3+
FD3–
FD2+
FD2–
DVDD
FD1+
FD1–
FD0+
FD0–
SYNC
CSB
CLK–
CLK+
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
DRVDD
D1–
D1+
D2–
D2+
D3–
D3+
D4–
D4+
DCO–
DCO+
D5–
D5+
D6–
D6+
D7–
SCLK/DFS
SDIO/DCS
AVDD
AVDD
VIN+B
VIN–B
RBIAS
CML
SENSE
VREF
VIN–A
VIN+A
AVDD
SMI SDFS
SMI SCLK/PDWN
SMI SDO/O EB
48
47
46
45
44
43
42
41
40
39
38
37
36
35
34
33
AD6655
PARAL LEL LVDS
TOP VI EW
(No t t o Scal e)
EXPOSED PADDLE, PI N 0
(BOTTOM OF PACKAGE)
06709-003
NOTES
1. THE EXPOSED THERMAL PAD ON T HE BOTTOM OF THEPACKAGE P ROVIDES THE
ANALOG GRO UND FO R THE PART. T HIS EXPO SED PAD MUS T BE CONNECTED TO
GROUND FOR PROPE R OPE RATION.
Figure 10. LFCSP Interleaved Parallel LVDS Pin Configuration (Top View)
Table 13. Pin Function Descriptions (Interleaved Parallel LVDS Mode)
Pin No. Mnemonic Type Description
ADC Power Supplies
20, 64
DRGND
Ground
Digital Output Ground.
1, 21 DRVDD Supply Digital Output Driver Supply (1.8 V to 3.3 V).
24, 57 DVDD Supply Digital Power Supply (1.8 V Nominal.)
36, 45, 46 AVDD Supply Analog Power Supply (1.8 V Nominal.)
0 AGND,
Exposed Pad
Ground Analog Ground. The exposed thermal pad on the bottom of the package provides the analog
ground for the part. This exposed pad must be connected to ground for proper operation.
ADC Analog
37
VIN+A
Input
Differential Analog Input Pin (+) for Channel A.
38 VIN−A Input Differential Analog Input Pin (−) for Channel A.
44 VIN+B Input Differential Analog Input Pin (+) for Channel B.
43 VIN−B Input Differential Analog Input Pin (−) for Channel B.
39 VREF Input/Output Voltage Reference Input/Output.
40 SENSE Input Voltage Reference Mode Select. See Table 15 for details.
42
RBIAS
Input/Output
External Reference Bias Resistor.
41 CML Output Common-Mode Level Bias Output for Analog Inputs.
49 CLK+ Input ADC Clock Input—True.
50 CLK− Input ADC Clock Input—Complement.
ADC Fast Detect Outputs
54 FD0+ Output Channel A/Channel B LVDS Fast Detect Indicator 0—True. See Table 21 for details.
53 FD0- Output Channel A/Channel B LVDS Fast Detect Indicator 0—Complement. See Table 21 for details.
56
FD1+
Output
Channel A/Channel B LVDS Fast Detect Indicator 1—True. See Table 21 for details.
55 FD1− Output Channel A/Channel B LVDS Fast Detect Indicator 1—Complement. See Table 21 for details.
59 FD2+ Output Channel A/Channel B LVDS Fast Detect Indicator 2—True See Table 21 for details.
58 FD2− Output Channel A/Channel B LVDS Fast Detect Indicator 2—Complement. See Table 21 for details.
61 FD3+ Output Channel A/Channel B LVDS Fast Detect Indicator 3—True. See Table 21 for details.
60 FD3− Output Channel A/Channel B LVDS Fast Detect Indicator 3—Complement. See Table 21 for details.
AD6655 Data Sheet
Rev. B | Page 22 of 84
Pin No. Mnemonic Type Description
Digital Input
52 SYNC Input Digital Synchronization Pin. Slave mode only.
Digital Outputs
63 D0+ (LSB) Output Channel A/Channel B LVDS Output Data 0—True.
62 D0− (LSB) Output Channel A/Channel B LVDS Output Data 0—Complement.
3 D1+ Output Channel A/Channel B LVDS Output Data 1—True.
2 D1− Output Channel A/Channel B LVDS Output Data 1—Complement.
5 D2+ Output Channel A/Channel B LVDS Output Data 2—True.
4 D2− Output Channel A/Channel B LVDS Output Data 2—Complement.
7 D3+ Output Channel A/Channel B LVDS Output Data 3—True.
6
D3−
Output
Channel A/Channel B LVDS Output Data 3—Complement.
9 D4+ Output Channel A/Channel B LVDS Output Data 4—True.
8 D4− Output Channel A/Channel B LVDS Output Data 4—Complement.
13 D5+ Output Channel A/Channel B LVDS Output Data 5—True.
12 D5− Output Channel A/Channel B LVDS Output Data 5—Complement.
15 D6+ Output Channel A/Channel B LVDS Output Data 6—True.
14 D6− Output Channel A/Channel B LVDS Output Data 6—Complement.
17 D7+ Output Channel A/Channel B LVDS Output Data 7—True.
16 D7− Output Channel A/Channel B LVDS Output Data 7—Complement.
19 D8+ Output Channel A/Channel B LVDS Output Data 8—True.
18 D8− Output Channel A/Channel B LVDS Output Data 8—Complement.
23
D9+
Output
Channel A/Channel B LVDS Output Data 9—True.
22 D9− Output Channel A/Channel B LVDS Output Data 9—Complement.
26 D10+ Output Channel A/Channel B LVDS Output Data 10—True.
25 D10− Output Channel A/Channel B LVDS Output Data 10—Complement.
28 D11+ Output Channel A/Channel B LVDS Output Data 11—True.
27 D11− Output Channel A/Channel B LVDS Output Data 11—Complement.
30
D12+
Output
Channel A/Channel B LVDS Output Data 12—True.
29 D12− Output Channel A/Channel B LVDS Output Data 12—Complement.
32 D13+ (MSB) Output Channel A/Channel B LVDS Output Data 13—True.
31 D13− (MSB) Output Channel A/Channel B LVDS Output Data 13—Complement.
11 DCO+ Output Channel A/Channel B LVDS Data Clock Output—True.
10
DCO−
Output
Channel A/Channel B LVDS Data Clock Output—Complement.
SPI Control
48
SCLK/DFS
Input
SPI Serial Clock/Data Format Select Pin in External Pin Mode.
47 SDIO/DCS Input/Output SPI Serial Data I/O/Duty Cycle Stabilizer in External Pin Mode.
51 CSB Input SPI Chip Select (Active Low).
Signal Monitor Port
33 SMI SDO/OEB Input/Output Signal Monitor Serial Data Output/Output Enable Input (Active Low) in External Pin Mode.
35 SMI SDFS
Output Signal Monitor Serial Data Frame Sync.
34 SMI SCLK/PDWN
Input/Output Signal Monitor Serial Clock Output/Power-Down Input (Active High) in External Pin Mode.
Data Sheet AD6655
Rev. B | Page 23 of 84
EQUIVALENT CIRCUITS
VIN
06709-004
Figure 11. Equivalent Analog Input Circuit
1.2V
10kΩ 10kΩ
CLK+ CLK–
AVDD
06709-005
Figure 12. Equivalent Clock lnput Circuit
DRVDD
DRGND
06709-006
Figure 13. Equivalent Digital Output Circuit
SDIO/DCS 1kΩ
26kΩ
DRVDD
DRVDD
06709-007
Figure 14. Equivalent SDIO/DCS Circuit or SMI SDFS Circuit
SCLK/DFS 1kΩ
26kΩ
06709-008
Figure 15. Equivalent SCLK/DFS Input Circuit
SENSE 1kΩ
06709-009
Figure 16. Equivalent SENSE Circuit
CSB 1kΩ
26kΩ
AVDD
06709-010
Figure 17. Equivalent CSB Input Circuit
VREF
AVDD
6kΩ
06709-011
Figure 18. Equivalent VREF Circuit
.
AD6655 Data Sheet
Rev. B | Page 24 of 84
TYPICAL PERFORMANCE CHARACTERISTICS
AVDD = 1.8 V, DVDD = 1.8 V, DRVDD = 1.8 V, sample rate = 150 MSPS, DCS enabled, 1.0 V internal reference, 2 V p-p differential
input, VIN = −1.0 dBFS, 64k sample, TA = 25°C, NCO enabled, FIR filter enabled, unless otherwise noted. In the FFT plots that follow,
the location of the second and third harmonics is noted when they fall in the pass band of the filter.
0
–20
–40
–60
–80
–100
–120
–140 035302520
15105
AMPLITUDE (dBFS)
FREQUENCY (MHz)
150MSPS
2.4M Hz @ –1d BFS
SNR = 74. 7dBc (75.7d BFS)
SF DR = 86.5d Bc
fNCO
= 18.75M Hz
SECOND HARMO NIC
THIRD HARMO NIC
06709-018
Figure 19. AD6655-150 Single-Tone FFT with fIN = 2.4 MHz, fNCO = 18.75 MHz
0
–20
–40
–60
–80
–100
–120
–140 03530252015
105
AMPLITUDE (dBFS)
FREQUENCY (MHz)
150MSPS
30.3M Hz @ –1d BFS
SNR = 74. 8dBc (75.8d BFS)
SF DR = 100dBc
fNCO
= 24MHz
06709-019
Figure 20. AD6655-150 Single-Tone FFT with fIN = 30.3 MHz, fNCO = 24 MHz
0
–20
–40
–60
–80
–100
–120
–140 03530252015105
AMPLITUDE (dBFS)
FREQUENCY (MHz)
150MSPS
140.1M Hz @ –1d BFS
SNR = 74. 3dBc (75.3d BFS)
SF DR = 83.3d Bc
fNCO
= 56MHz
THIRD HARMO NIC
06709-020
Figure 21. AD6655-150 Single-Tone FFT with fIN = 70.1 MHz, fNCO = 56 MHz
0
–20
–40
–60
–80
–100
–120
–140 035
3025201510
5
AMPLITUDE (dBFS)
FREQUENCY (MHz)
150MSPS
140.1M Hz @ –1d BFS
SNR = 73. 7dBc (74.7d BFS)
SF DR = 82.8d Bc
fNCO
= 126MHz
SECOND HARMO NICTHIRD HARMO NIC
06709-021
Figure 22. AD6655-150 Single-Tone FFT with fIN = 140.1 MHz,
fNCO = 126 MHz
0
–20
–40
–60
–80
–100
–120
–140 03530252015105
AMPLITUDE (dBFS)
FREQUENCY (MHz)
150MSPS
220.1M Hz @ –1d BFS
SNR = 71. 8dBc (72.8d BFS)
SF DR = 81.4d Bc
fNCO
= 205MHz
THIRD HARMO NIC
06709-022
Figure 23. AD6655-150 Single-Tone FFT with fIN = 220.1 MHz,
fNCO = 205 MHz
0
–20
–40
–60
–80
–100
–120
–140 03530252015105
AMPLITUDE (dBFS)
FREQUENCY (MHz)
150MSPS
332.1M Hz @ –1d BFS
SNR = 71. 7dBc (72.7d BFS)
SF DR = 95.0d Bc
fNCO
= 321.5M Hz
06709-023
Figure 24. AD6655-150 Single-Tone FFT with fIN = 332.1 MHz,
fNCO = 321.5 MHz
Data Sheet AD6655
Rev. B | Page 25 of 84
0
–20
–40
–60
–80
–100
–120
–140 035
30
2520
15
105
AMPLITUDE (dBFS)
FREQUENCY (MHz)
150MSPS
445.1M Hz @ –1d BFS
SNR = 67. 4dBc (65.4d BFS)
SF DR = 74.1d Bc
fNCO
= 429MHz
SECOND HARMO NIC
THIRD HARMO NIC
06709-024
Figure 25. AD6655-150 Single-Tone FFT with fIN = 445.1 MHz, fNCO = 429 MHz
0
–20
–40
–60
–80
–100
–120
–140 03025
20
15
105
AMPLITUDE (dBFS)
FREQUENCY (MHz)
125MSPS
2.4M Hz @ –1d BFS
SNR = 74. 5dBc (75.5d BFS)
SF DR = 87.8d Bc
fNCO
= 15.75M Hz
SECOND HARMO NIC
THIRD HARMO NIC
06709-025
Figure 26. AD6655-125 Single-Tone FFT with fIN =2.4 MHz, fNCO = 15.75 MHz
0
–20
–40
–60
–80
–100
–120
–140 030
25201510
5
AMPLITUDE (dBFS)
FREQUENCY (MHz)
125MSPS
30.3M Hz @ –1d BFS
SNR = 74. 7dBc (75.7d BFS)
SF DR = 89.6d Bc
fNCO
= 21MHz
THIRD
HARMONIC
06709-026
Figure 27. AD6655-125 Single-Tone FFT with fIN = 30.3 MHz, fNCO = 21 MHz
0
–20
–40
–60
–80
–100
–120
–140 030252015105
AMPLITUDE (dBFS)
FREQUENCY (MHz)
125MSPS
70.3M Hz @ –1d BFS
SNR = 74. 6dBc (75.6d BFS)
SF DR = 86.1d Bc
fNCO
= 78MHz
THIRD HARMO NIC
06709-027
Figure 28. AD6655-125 Single-Tone FFT with fIN = 70.3 MHz, fNCO = 78 MHz
0
–20
–40
–60
–80
–100
–120
–140 030252015
105
AMPLITUDE (dBFS)
FREQUENCY (MHz)
125MSPS
140.1M Hz @ –1d BFS
SNR = 74. 1dBc (75.1d BFS)
SF DR = 90.3d Bc
fNCO
= 142MHz
THIRD HARMO NIC
06709-028
Figure 29. AD6655-125 Single-Tone FFT with fIN = 140.1 MHz, fNCO = 142 MHz
0
–20
–40
–60
–80
–100
–120
–140 030252015105
AMPLITUDE (dBFS)
FREQUENCY (MHz)
125MSPS
220.1M Hz @ –1d BFS
SNR = 73. 4dBc (74.4d BFS)
SF DR = 90.2d Bc
fNCO
= 231MHz
06709-029
Figure 30. AD6655-125 Single-Tone FFT with fIN = 220.1 MHz, fNCO = 231 MHz
AD6655 Data Sheet
Rev. B | Page 26 of 84
120
0
20
40
60
80
100
–90 0–10–20
–30–40
–50
–60–70
–80
SNR/ S FDR (d Bc AND dBF S )
INPUT AMPLITUDE (dBFS)
SF DR ( dBc)
SF DR ( dBFS )
SNR (dBFS )
SNR (dBc)
85dB
REF E RE NCE LINE
06709-030
Figure 31. AD6655-150 Single-Tone SNR/SFDR vs. Input Amplitude (AIN) with
fIN = 2.4 MHz, fNCO = 18.75 MHz
120
0
20
40
60
80
100
–90 0
–10–20–30–40
–50–60–70
–80
SNR/ S FDR (d Bc AND dBF S )
INPUT AMPLITUDE (dBFS)
SF DR ( dBc)
SF DR ( dBFS )
SNR (dBFS )
SNR (dBc)
85dB
REF E RE NCE LINE
06709-031
Figure 32. AD6655-150 Single-Tone SNR/SFDR vs. Input Amplitude (AIN) with
fIN = 98.12 MHz, fNCO = 100.49 MHz
95
90
85
80
75
70
65
60 0450400350
300250200150
10050
SNR/ S FDR (d Bc)
INP UT FRE QUENCY ( M Hz )
SF DR = + 25°C
SF DR = + 85°C
SF DR = –40°C
SNR = +25°C
SNR = +85°C
SNR = –40°C
06709-032
Figure 33. AD6655-125 Single-Tone SNR/SFDR vs. Input Frequency (fIN) and
Temperature with DRVDD = 1.8 V
95
90
85
80
75
70
65
60 045040035030025020015010050
SNR/ S FDR (d Bc)
INP UT FRE QUENCY ( M Hz )
SF DR = + 25°C
SF DR = + 85°C
SF DR = –40°C
SNR = +25°C
SNR = +85°C
SNR = –40°C
06709-033
Figure 34. AD6655-125 Single-Tone SNR/SFDR vs. Input Frequency (fIN) and
Temperature with DRVDD = 3.3 V
–1.5
–4.0
–3.5
–3.0
–2.5
–2.0
0.5
0
0.1
0.2
0.3
0.4
–40 806040200
–20
GAIN ERRO R ( %FSR)
OFFSET ERROR (%FSR)
TEMPERATURE (°C)
06709-034
OFFSET
GAIN
Figure 35. AD6655-150 Gain and Offset vs. Temperature
0
–120
–100
–80
–60
–40
–20
–90 –78 –66 –54 –42 –30 –18 –6
SF DR/IM D3 ( dBc AND d BFS)
INPUT AMPLITUDE (dBFS)
SF DR ( dBc)
SF DR ( dBFS ) IMD3 ( dBFS )
IM D3 ( dBc)
06709-035
Figure 36. AD6655-150 Two-Tone SFDR/IMD3 vs. Input Amplitude (AIN) with
fIN1 = 29.12 MHz, fIN2 = 32.12 MHz, fS = 150 MSPS, fNCO = 22 MHz
Data Sheet AD6655
Rev. B | Page 27 of 84
0
–120
–100
–80
–60
–40
–20
–90 –78 –66 –54 –42 –30 –18 –6
SF DR/IM D3 ( dBc AND d BFS)
INPUT AMPLITUDE (dBFS)
SF DR ( dBc)
SF DR ( dBFS ) IMD3 ( dBFS )
IM D3 ( dBc)
06709-036
Figure 37. AD6655-150 Two-Tone SFDR/IMD3 vs. Input Amplitude (AIN) with
fIN1 = 169.12 MHz, fIN2 = 172.12 MHz, fS = 150 MSPS, fNCO = 177 MHz
0
–20
–40
–60
–80
–100
–120
–140 0 5 10 15 20 25 30
06709-037
AMPLITUDE (dBFS)
FREQUENCY (MHz)
Figure 38. AD6655-125, Two 64k WCDMA Carriers with fIN = 170 MHz,
fS = 122.88 MHz, fNCO = 168.96 MHz
0
–20
–40
–60
–80
–100
–120
–140 03530252015105
AMPLITUDE (dBFS)
FREQUENCY (MHz)
150MSPS
29.12M Hz @ –7d BFS
32.12M Hz @ –7d BFS
SF DR = 89.1d Bc ( 96.1d BFS)
fNCO
= 22MHz
06709-038
Figure 39. AD6655-150 Two-Tone FFT with fIN1 = 29.12 MHz, fIN2 = 32.12 MHz,
fS = 150 MSPS, fNCO = 22 MHz
0
–20
–40
–60
–80
–100
–120
–140 03530252015105
AMPLITUDE (dBFS)
FREQUENCY (MHz)
150MSPS
169.12M Hz @ –7d BFS
172.12M Hz @ –7d BFS
SF DR = 85.5d Bc ( 92.5d BFS)
fNCO
= 177MHz
06709-039
Figure 40. AD6655-150 Two Tone FFT with fIN1 = 169.12 MHz,
fIN2 = 172.12 MHz, fS = 150 MSPS, fNCO = 177 MHz
0
–20
–40
–60
–80
–100
–120
–140 037.5
30.022.515.0
7.5
AMPLITUDE (dBFS)
FREQUENCY (MHz)
NPR = 64. 5dBc
NOTCH @ 18.5M Hz
NOTCH WIDT H = 3M Hz
06709-040
Figure 41. AD6655-150 Noise Power Ratio (NPR)
95
85
75
65 025 50 75 100 125 150
06709-041
SNR/ S FDR (d Bc)
SAMPLE RATE (MSPS)
SF DR ( dBc)
SNR (dBc)
Figure 42. AD6655-150 Single-Tone SNR/SFDR vs. Sample Rate (fs) with
fIN = 2.3 MHz
AD6655 Data Sheet
Rev. B | Page 28 of 84
12
0
2
4
6
8
10
NUMBER OF HIT S ( 1M )
OUTPUT CODE
N – 3 N – 2 N – 1 NN + 1 N + 2 N + 3
0.85 LSB rms
06709-042
Figure 43. AD6655 Grounded Input Histogram
90
85
80
75
70
SNR/ S FDR (d Bc)
DUTY CY CLE (%)
SF DR DCS ON
SNR DCS ON
SF DR DCS OFF
SNR DCS OFF
20 30 40 50 60 70 80
06709-043
Figure 44. AD6655-150 SNR/SFDR vs. Duty Cycle with fIN = 30.3 MHz,
fNCO = 45 MHz
90
85
80
75
65
70
SNR/ S FDR (d Bc)
INPUT COMMON-MODE VOLT AGE (V)
SNR
SFDR
0.2 0.4 0.6 0.8 1.0 1.2 1.4
06709-044
Figure 45. AD6655-150 SNR/SFDR vs. Input Common Mode (VCM) with
fIN = 30.3 MHz, fNCO = 45 MHz
Data Sheet AD6655
Rev. B | Page 29 of 84
THEORY OF OPERATION
The AD6655 has two analog input channels, two decimating
channels, and two digital output channels. The intermediate
frequency (IF) input signal passes through several stages before
appearing at the output port(s) as a filtered, decimated digital
signal.
The dual ADC design can be used for diversity reception of
signals, where the ADCs operate identically on the same carrier
but from two separate antennae. The ADCs can also be operated
with independent analog inputs. The user can sample any fS/2
frequency segment from dc to 150 MHz using appropriate low-
pass or band-pass filtering at the ADC inputs with little loss
in ADC performance. Operation to 450 MHz analog input is
permitted but occurs at the expense of increased ADC noise and
distortion.
In nondiversity applications, the AD6655 can be used as a base-
band receiver, where one ADC is used for I input data, and the
other is used for Q input data.
Synchronization capability is provided to allow synchronized
timing between multiple channels or multiple devices. The
NCO phase can be set to produce a known offset relative to
another channel or device.
Programming and control of the AD6655 are accomplished
using a 3-bit SPI-compatible serial interface.
ADC ARCHITECTURE
AD6655 architecture consists of a front-end sample-and-hold
amplifier (SHA) followed by a pipelined, switched-capacitor ADC.
The quantized outputs from each stage are combined into a final
14-bit result in the digital correction logic. The pipelined archi-
tecture permits the first stage to operate on a new input sample
and the remaining stages to operate on the preceding samples.
Sampling occurs on the rising edge of the clock.
Each stage of the pipeline, excluding the last, consists of a low
resolution flash ADC connected to a switched-capacitor digital-
to-analog converter (DAC) and an interstage residue amplifier
(MDAC). The residue amplifier magnifies the difference between
the reconstructed DAC output and the flash input for the next
stage in the pipeline. One bit of redundancy is used in each stage
to facilitate digital correction of flash errors. The last stage
simply consists of a flash ADC.
The input stage of each channel contains a differential SHA that
can be ac- or dc-coupled in differential or single-ended modes.
The output staging block aligns the data, corrects errors, and
passes the data to the output buffers. The output buffers are
powered from a separate supply, allowing adjustment of the
output voltage swing. During power-down, the output buffers
go into a high impedance state.
ANALOG INPUT CONSIDERATIONS
The analog input to the AD6655 is a differential switched-
capacitor SHA that has been designed for optimum performance
while processing a differential input signal.
The clock signal alternatively switches the SHA between sample
mode and hold mode (see Figure 46). When the SHA is switched
into sample mode, the signal source must be capable of charging
the sample capacitors and settling within 1/2 of a clock cycle.
A small resistor in series with each input can help reduce the
peak transient current required from the output stage of the
driving source. A shunt capacitor can be placed across the inputs
to provide dynamic charging currents. This passive network creates
a low-pass filter at the ADC input; therefore, the precise values
are dependent on the application.
In IF undersampling applications, any shunt capacitors should be
reduced. In combination with the driving source impedance,
the shunt capacitors limit the input bandwidth. Refer to Appli-
cation Note AN-742, Frequency Domain Response of Switched-
Capacitor ADCs; Application Note AN-827, A Resonant Approach
to Interfacing Amplifiers to Switched-Capacitor ADCs; and the
Analog Dialogue article, “Transformer-Coupled Front-End for
Wideband A/D Converters,” for more information on this subject
(see www.analog.com). In general, the precise values are dependent
on the application.
VIN+
VIN–
CPIN, PAR
CPIN, PAR
CS
CS
CH
CH
H
S
S
S
S
06709-048
Figure 46. Switched-Capacitor SHA Input
For best dynamic performance, the source impedances driving
VIN+ and VIN− should be matched such that common-mode
settling errors are symmetrical. These errors are reduced by the
common-mode rejection of the ADC.
An internal differential reference buffer creates positive and
negative reference voltages that define the input span of the
ADC core. The output common mode of the reference buffer is
set to VCMREF (approximately 1.6 V).
Input Common Mode
The analog inputs of the AD6655 are not internally dc biased.
In ac-coupled applications, the user must provide this bias
externally. Setting the device so that VCM = 0.55 × AVDD is
recommended for optimum performance, but the device functions
over a wider range with reasonable performance (see Figure 45).
AD6655 Data Sheet
Rev. B | Page 30 of 84
An on-board common-mode voltage reference is included in
the design and is available from the CML pin. Optimum perform-
ance is achieved when the common-mode voltage of the analog
input is set by the CML pin voltage (typically 0.55 × AVDD).
Differential Input Configurations
Optimum performance is achieved while driving the AD6655
in a differential input configuration. For baseband applications,
the AD8138, ADA4937-2, and ADA4938-2 differential drivers
provide excellent performance and a flexible interface to the
ADC. The output common-mode voltage of the AD8138 is
easily set with the CML pin of the AD6655 (see Figure 47), and
the driver can be configured in a Sallen-Key filter topology to
provide band limiting of the input signal.
AVDD
1V p-p 49.9Ω
523Ω
0.1µF
R
R
C
499Ω
499Ω
499Ω
AD8138
AD6655
VIN+
VIN– CML
06709-049
Figure 47. Differential Input Configuration Using the AD8138
For baseband applications where SNR is a key parameter,
differential transformer coupling is the recommended input
configuration. An example is shown in Figure 48. To bias the
analog input, the CML voltage can be connected to the center
tap of the secondary winding of the transformer.
2V p-p 49.9Ω
0.1µF
R
R
C
AD6655
VIN+
VIN– CML
06709-050
Figure 48. Differential Transformer-Coupled Configuration
The signal characteristics must be considered when selecting
a transformer. Most RF transformers saturate at frequencies
below a few megahertz (MHz). Excessive signal power can also
cause core saturation, which leads to distortion.
At input frequencies in the second Nyquist zone and above, the
noise performance of most amplifiers is not adequate to achieve
the true SNR performance of the AD6655. For applications where
SNR is a key parameter, differential double balun coupling is
the recommended input configuration (see Figure 49).
An alternative to using a transformer-coupled input at frequencies
in the second Nyquist zone is to use the AD8352 differential
driver is shown in Figure 50. See the AD8352 data sheet for
more information. In addition, if the application requires an
amplifier with variable gain, the AD8375 or AD8376 digital
variable gain amplifiers (DVGAs) provide good performance
driving the AD6655.
In any configuration, the value of the shunt capacitor, C, is
dependent on the input frequency and source impedance and
may need to be reduced or removed. Table 14 displays recom-
mended values to set the RC network. However, these values are
dependent on the input signal and should be used only as a
starting guide.
Table 14. Example RC Network
Frequency Range
(MHz)
R Series
(Ω, Each)
C Differential
(pF)
0 to 70 33 15
70 to 200 33 5
200 to 300 15 5
>300 15 Open
AD6655
R
0.1µF
0.1µF
2V p-p VIN+
VIN– CML
C
R
0.1µF
S0.1µF
25Ω
25Ω
SPAP
06709-051
Figure 49. Differential Double Balun Input Configuration
AD6655
AD8352
0Ω
R
0Ω
C
D
R
D
R
G
0.1µF
0.1µF
0.1µF
VIN+
VIN– CML
C
0.1µF
16
1
2
3
4
5
11
R
0.1µF
0.1µF
10
14
0.1µF
8, 13
VCC
200Ω
200Ω
ANALOG INPUT
ANALOG INPUT
06709-052
Figure 50. Differential Input Configuration Using the AD8352
Data Sheet AD6655
Rev. B | Page 31 of 84
Single-Ended Input Configuration
A single-ended input can provide adequate performance in
cost-sensitive applications. In this configuration, SFDR and
distortion performance degrade due to the large input common-
mode swing. If the source impedances on each input are matched,
there should be little effect on SNR performance. Figure 51 shows
a typical single-ended input configuration.
2V p-p
R
R
C
49.9Ω 0.1µF
10µF
10µF0.1µF
AVDD
1kΩ
1kΩ
1kΩ
1kΩ
AD6655
AVDD
VIN+
VIN–
06709-053
Figure 51. Single-Ended Input Configuration
VOLTAGE REFERENCE
A stable and accurate voltage reference is built into the AD6655.
The input range can be adjusted by varying the reference voltage
applied to the AD6655, using either the internal reference or an
externally applied reference voltage. The input span of the ADC
tracks reference voltage changes linearly. The various reference
modes are summarized in the sections that follow. The Reference
Decoupling section describes the best practices PCB layout of
the reference.
Internal Reference Connection
A comparator within the AD6655 detects the potential at the
SENSE pin and configures the reference into four possible modes,
which are summarized in Table 15. If SENSE is grounded, the
reference amplifier switch is connected to the internal resistor
divider (see Figure 52), setting VREF to 1.0 V. Connecting the
SENSE pin to VREF switches the reference amplifier output to
the SENSE pin, completing the loop and providing a 0.5 V
reference output. If a resistor divider is connected externally
to the chip, as shown in Figure 53, the switch again sets to the
SENSE pin.
This puts the reference amplifier in a noninverting mode with
the VREF output defined as follows:
+×= R1
R2
VREF 15.0
The input range of the ADC always equals twice the voltage at
the reference pin for either an internal or an external reference.
VREF
SENSE
0.5V
AD6655
SELECT
LOGIC
0.1µF
1.0µF
VIN–A/VIN–B
VIN+A/VIN+B
ADC
CORE
06709-054
Figure 52. Internal Reference Configuration
0.5V
AD6655
SELECT
LOGIC
VIN–A/VIN–B
VIN+A/VIN+B
ADC
CORE
VREF
SENSE
0.1µF1.0µF R2
R1
06709-055
Figure 53. Programmable Reference Configuration
Table 15. Reference Configuration Summary
Selected Mode SENSE Voltage Resulting VREF (V)
Resulting Differential
Span (V p-p)
External Reference AVDD N/A 2 × external reference
Internal Fixed Reference VREF 0.5 1.0
Programmable Reference 0.2 V to VREF
+× R1
R2
15
.0
(see Figure 53) 2 × VREF
Internal Fixed Reference AGND to 0.2 V 1.0 2.0
AD6655 Data Sheet
Rev. B | Page 32 of 84
If the internal reference of the AD6655 is used to drive multiple
converters to improve gain matching, the loading of the reference
by the other converters must be considered. Figure 54 depicts
how the internal reference voltage is affected by loading.
0
–1.25 02.0
LOAD CURRENT ( mA)
REF E RE NCE V OLTAG E E RROR (%)
–0.25
–0.50
–0.75
–1.00
0.5 1.0 1.5
VREF = 0. 5V
VREF = 1. 0V
06709-056
Figure 54. VREF Accuracy vs. Load
External Reference Operation
The use of an external reference may be necessary to enhance
the gain accuracy of the ADC or improve thermal drift charac-
teristics. Figure 55 shows the typical drift characteristics of the
internal reference in both 1.0 V and 0.5 V modes.
2.5
–2.5
–40
TEMPERATURE (°C)
REF E RE NCE V OLTAG E E RROR (mV )
2.0
1.5
1.0
0.5
0
–0.5
–1.0
–1.5
–2.0
–20 020 40 60 80
06709-057
Figure 55. Typical VREF Drift
When the SENSE pin is tied to AVDD, the internal reference is
disabled, allowing the use of an external reference. An internal
reference buffer loads the external reference with an equivalent
6 kΩ load (see Figure 18). The internal buffer generates the positive
and negative full-scale references for the ADC core. Therefore,
the external reference must be limited to a maximum of 1.0 V.
CLOCK INPUT CONSIDERATIONS
For optimum performance, the AD6655 sample clock inputs,
CLK+ and CLK−, should be clocked with a differential signal.
The signal is typically ac-coupled into the CLK+ and CLK− pins
via a transformer or capacitors. These pins are biased internally
(see Figure 56) and require no external bias.
1.2V
AVDD
2pF 2pF
CLK–CLK+
06709-058
Figure 56. Equivalent Clock Input Circuit
Clock Input Options
The AD6655 has a very flexible clock input structure. Clock
input can be a CMOS, LVDS, LVPECL, or sine wave signal.
Regardless of the type of signal being used, clock source jitter
is of the most concern, as described in the Jitter Considerations
section.
Figure 57 and Figure 58 show two preferred methods for clocking
the AD6655 (at clock rates to up to 625 MHz). A low jitter clock
source is converted from a single-ended signal to a differential
signal using an RF transformer. The back-to-back Schottky diodes
across the transformer secondary limit clock excursions into the
AD6655 to approximately 0.8 V p-p differential. This helps prevent
the large voltage swings of the clock from feeding through to other
portions of the AD6655, while preserving the fast rise and fall times
of the signal, which are critical to a low jitter performance.
0.1µF
0.1µF
0.1µF0.1µF
SCHOTTKY
DIODES:
HSMS2822
CLOCK
INPUT 50Ω 100Ω
CLK–
CLK+
ADC
AD6655
Mini-Circuits®
ADT1–1W T, 1: 1Z
XFMR
06709-059
Figure 57. Transformer Coupled Differential Clock (Up to 200 MHz)
0.1µF
0.1µF1nF
CLOCK
INPUT
1nF
50Ω
CLK–
CLK+
ADC
AD6655
SCHOTTKY
DIODES:
HSMS2822
06709-157
Figure 58. Balun-Coupled Differential Clock (Up to 625 MHz)
If a low jitter clock source is not available, another option is to
ac couple a differential PECL signal to the sample clock input
pins as shown in Figure 59. The AD9510/AD9511/AD9512/
AD9513/AD9514/AD9515/AD9516 clock drivers offer excellent
jitter performance.
Data Sheet AD6655
Rev. B | Page 33 of 84
100Ω
0.1µF
0.1µF
0.1µF
0.1µF
240Ω240Ω
AD951x
PECL DRIVER
50kΩ 50kΩ
CLK–
CLK+
ADC
AD6655
CLOCK
INPUT
CLOCK
INPUT
06709-060
Figure 59. Differential PECL Sample Clock (Up to 625 MHz)
A third option is to ac-couple a differential LVDS signal to the
sample clock input pins, as shown in Figure 60. The AD9510/
AD9511/AD9512/AD9513/AD9514/AD9515/AD9516 clock
drivers offer excellent jitter performance.
100Ω
0.1µF
0.1µF
0.1µF
0.1µF
50kΩ 50kΩ
CLK–
CLK+
ADC
AD6655
CLOCK
INPUT
CLOCK
INPUT
AD951x
LVDS DRIVER
06709-061
Figure 60. Differential LVDS Sample Clock (Up to 625 MHz)
In some applications, it may be acceptable to drive the sample
clock inputs with a single-ended CMOS signal. In such applica-
tions, the CLK+ pin should be driven directly from a CMOS
gate, and the CLK− pin should be bypassed to ground with a
0.1 µF capacitor in parallel with a 39 kΩ resistor (see Figure 61).
CLK+ can be driven directly from a CMOS gate. Although the
CLK+ input circuit supply is AVDD (1.8 V), this input is designed
to withstand input voltages of up to 3.6 V, making the selection
of the drive logic voltage very flexible.
OPTIONAL
100Ω 0.1µF
0.1µF
0.1µF
39kΩ
50Ω
CLK–
CLK+
ADC
AD6655
V
CC
1kΩ
1kΩ
CLOCK
INPUT AD951x
CMOS DRIVER
06709-062
Figure 61. Single-Ended 1.8 V CMOS Sample Clock (Up to 150 MSPS)
OPTIONAL
100Ω 0.1µF
0.1µF
0.1µF
V
CC
50Ω
CLK–
CLK+
ADC
AD6655
1kΩ
1kΩ
CLOCK
INPUT AD951x
CMOS DRIVER
06709-063
Figure 62. Single-Ended 3.3 V CMOS Sample Clock (Up to 150 MSPS)
Input Clock Divider
The AD6655 contains an input clock divider with the ability to
divide the input clock by integer values between 1 and 8. If a divide
ratio other than 1 is selected, the duty cycle stabilizer is auto-
matically enabled.
The AD6655 clock divider can be synchronized using the external
SYNC input. Bit 1 and Bit 2 of Register 0x100 allow the clock
divider to be resynchronized on every SYNC signal or only on
the first SYNC signal after the register is written. A valid SYNC
causes the clock divider to reset to its initial state. This synchro-
nization feature allows multiple parts to have their clock dividers
aligned to guarantee simultaneous input sampling.
Clock Duty Cycle
Typical high speed ADCs use both clock edges to generate a
variety of internal timing signals and, as a result, may be sensitive to
clock duty cycle. Commonly, a ±5% tolerance is required on the
clock duty cycle to maintain dynamic performance characteristics.
The AD6655 contains a duty cycle stabilizer (DCS) that retimes
the nonsampling (falling) edge, providing an internal clock
signal with a nominal 50% duty cycle. This allows the user to
provide a wide range of clock input duty cycles without affecting
the performance of the AD6655. Noise and distortion performance
are nearly flat for a wide range of duty cycles with the DCS on, as
shown in Figure 44.
Jitter on the rising edge of the input clock is still of paramount
concern and is not easily reduced by the internal stabilization
circuit. The duty cycle control loop does not function for clock
rates less than 20 MHz nominally. The loop has a time constant
associated with it that must be considered when the clock rate
can change dynamically. A wait time of 1.5 µs to 5 µs is required
after a dynamic clock frequency increase or decrease before the
DCS loop is relocked to the input signal. During the time
period that the loop is not locked, the DCS loop is bypassed,
and internal device timing is dependent on the duty cycle of the
input clock signal. In such applications, it may be appropriate to
disable the duty cycle stabilizer. In all other applications, enabling
the DCS circuit is recommended to maximize ac performance.
Jitter Considerations
High speed, high resolution ADCs are sensitive to the quality of
the clock input. The degradation in SNR at a given input
frequency (fIN) due to jitter (tJ) can be calculated by
SNRHF = −10 log[(2π × fIN × tJRMS)2 + 10
)10/(
LF
SNR/
]
In the equation, the rms aperture jitter represents the root-
mean-square of all jitter sources, which include the clock input,
the analog input signal, and the ADC aperture jitter specification.
IF undersampling applications are particularly sensitive to jitter,
as shown in Figure 63.
AD6655 Data Sheet
Rev. B | Page 34 of 84
75
70
65
60
55
50
45 1 10 100 1000
SNR (dBc)
INPUT F REQUENCY (MHz)
3.00ps
0.05ps
0.20ps
0.50ps
1.00ps
1.50ps
2.00ps
2.50ps
MEASURED
06709-064
Figure 63. SNR vs. Input Frequency and Jitter
The clock input should be treated as an analog signal in cases
where aperture jitter may affect the dynamic range of the AD6655.
Power supplies for clock drivers should be separated from the
ADC output driver supplies to avoid modulating the clock signal
with digital noise. Low jitter, crystal-controlled oscillators make
the best clock sources. If the clock is generated from another type
of source (by gating, dividing, or another method), it should be
retimed by the original clock at the last step.
Refer to Application Note AN-501 and Application Note AN-756
for more information about jitter performance as it relates to ADCs
(see www.analog.com).
POWER DISSIPATION AND STANDBY MODE
As shown in Figure 64 through Figure 67, the power dissipated
by the AD6655 is proportional to its sample rate. In CMOS
output mode, the digital power dissipation is determined
primarily by the strength of the digital drivers and the load on
each output bit. The maximum DRVDD current (IDRVDD) can be
calculated by
IDRVDD = VDRVDD × CLOAD × fCLK × N
where N is the number of output bits (30, in the case of the
AD6655, assuming the FD bits are inactive).
This maximum current occurs when every output bit switches
on every clock cycle, that is, a full-scale square wave at the
Nyquist frequency of fCLK/2. In practice, the DRVDD current
is established by the average number of output bits switching,
which is determined by the sample rate and the characteristics
of the analog input signal. Reducing the capacitive load presented
to the output drivers can minimize digital power consumption.
The data in Figure 64 through Figure 67 was taken using the same
operating conditions as those used for the Typical Performance
Characteristics, with a 5 pF load on each output driver.
1.50
1.25
1.00
0.75
0.50
0.25
0
0.6
I
AVDD
I
DVDD
I
DRVDD
0.5
0.4
0.3
0.2
0.1
0
0 50 100
TOTAL POWER (W)
SUPPLY CURRENT (A)
15025 75 125
SAMPLE RATE (MSPS)
TOTAL POWER
06709-065
Figure 64. AD6655-150 Power and Current vs. Sample Rate
1.50
1.25
1.00
0.75
0.50
0.25
0
0.6
0.5
I
AVDD
I
DVDD
I
DRVDD
0.4
0.3
0.2
0.1
0
075
TOTAL POWER (W)
SUPPLY CURRENT (A)
25 50 125100
SAMPLE RATE (MSPS)
TOTAL POWER
06709-166
Figure 65. AD6655-125 Power and Current vs. Sample Rate
1.25
1.00
0.75
0.50
0.25
0
0.5
0.4
I
AVDD
I
DVDD
I
DRVDD
0.3
0.2
0.1
0
075
TOTAL POWER (W)
SUPPL Y CURRENT (A)
25 50 100
SAMPLE RATE (MSPS)
TOTAL POWER
06709-167
Figure 66. AD6655-105 Power and Current vs. Sample Rate
Data Sheet AD6655
Rev. B | Page 35 of 84
1.00
0.75
0.50
0.25
0
0.4
IAVDD
IDVDD
IDRVDD
0.3
0.2
0.1
0
060
TOTAL POWER (W)
SUPPLY CURRENT (A)
20 40 80
SAMPLE RATE (MSPS)
TOTAL POWER
06709-168
Figure 67. AD6655-80 Power and Current vs. Sample Rate
By asserting PDWN (either through the SPI port or by asserting
the PDWN pin high), the AD6655 is placed in power-down
mode. In this state, the ADC typically dissipates 2.5 mW.
During power-down, the output drivers are placed in a high
impedance state. Asserting the PDWN pin low returns the
AD6655 to its normal operating mode. Note that PDWN is
referenced to the digital output driver supply (DRVDD) and
should not exceed that supply voltage. PDWN can be driven
with 1.8 V logic, even when DRVDD is at 3.3 V.
Low power dissipation in power-down mode is achieved by
shutting down the reference, reference buffer, biasing networks,
and clock. Internal capacitors are discharged when entering
power-down mode and then must be recharged when returning
to normal operation. As a result, wake-up time is related to the
time spent in power-down mode, and shorter power-down
cycles result in proportionally shorter wake-up times.
When using the SPI port interface, the user can place the ADC
in power-down mode or standby mode. Standby mode allows
the user to keep the internal reference circuitry powered when
faster wake-up times are required. See the Memory Map Register
Description section and Application Note AN-877, Interfacing
to High Speed ADCs via SPI at www.analog.com for additional
details.
DIGITAL OUTPUTS
The AD6655 output drivers can be configured to interface with
1.8 V to 3.3 V CMOS logic families by matching DRVDD to the
digital supply of the interfaced logic. Alternatively, the AD6655
outputs can be configured for either ANSI LVDS or reduced
drive LVDS using a 1.8 V DRVDD supply.
In CMOS output mode, the output drivers are sized to provide
sufficient output current to drive a wide variety of logic families.
However, large drive currents tend to cause current glitches on
the supplies that may affect converter performance. Applica-
tions requiring the ADC to drive large capacitive loads or large
fanouts may require external buffers or latches.
The output data format can be selected for either offset binary
or twos complement by setting the SCLK/DFS pin when operating
in the external pin mode (see Table 16). As detailed in Application
Note AN-877, Interfacing to High Speed ADCs via SPI, the data
format can be selected for offset binary, twos complement, or
gray code when using the SPI control.
Table 16. SCLK/DFS Mode Selection (External Pin Mode)
Voltage at Pin SCLK/DFS SDIO/DCS
AGND (default) Offset binary DCS disabled
AVDD Twos complement DCS enabled
Digital Output Enable Function (OEB)
The AD6655 has a flexible three-state ability for the digital output
pins. The three-state mode is enabled using the SMI SDO/OEB pin
or through the SPI interface. If the SMI SDO/OEB pin is low, the
output data drivers are enabled. If the SMI SDO/OEB pin is high,
the output data drivers are placed in a high impedance state.
This OEB function is not intended for rapid access to the data
bus. Note that OEB is referenced to the digital output driver
supply (DRVDD) and should not exceed that supply voltage.
OEB can be driven with 1.8 V logic even when DRVDD is at 3.3 V.
When using the SPI interface, the data and fast detect outputs of
each channel can be independently three-stated by using the
output enable bar bit (Bit 4) in Register 0x14.
Interleaved CMOS Mode
Setting Bit 5 in Register 0x14 enables interleaved CMOS output
mode. In this mode, output data is routed through Port A with
the ADC Channel A output data present on the rising edge of
DCO and the ADC Channel B output data present on the
falling edge of DCO.
Timing
The AD6655 provides latched data with a pipeline delay that is
dependent on which of the digital back end features are enabled.
Data outputs are available one propagation delay (tPD) after the
rising edge of the clock signal.
The length of the output data lines and loads placed on them
should be minimized to reduce transients within the AD6655.
These transients can degrade converter dynamic performance.
The lowest typical conversion rate of the AD6655 is 10 MSPS. At
clock rates below 10 MSPS, dynamic performance may degrade.
Data Clock Output (DCO)
The AD6655 also provides data clock output (DCO) intended for
capturing the data in an external register. Figure 2 through Figure 6
show a graphical timing description of the AD6655 output modes.
AD6655 Data Sheet
Rev. B | Page 36 of 84
Table 17. Output Data Format
Input (V) Condition (V) Offset Binary Output Mode Twos Complement Mode OR
VIN+ – VIN– < –VREF – 0.5 LSB 00 0000 0000 0000 10 0000 0000 0000 1
VIN+ – VIN– = –VREF 00 0000 0000 0000 10 0000 0000 0000 0
VIN+ – VIN– = 0 10 0000 0000 0000 00 0000 0000 0000 0
VIN+ – VIN– = +VREF – 1.0 LSB 11 1111 1111 1111 01 1111 1111 1111 0
VIN+ – VIN– > +VREF – 0.5 LSB 11 1111 1111 1111 01 1111 1111 1111 1
Data Sheet AD6655
Rev. B | Page 37 of 84
DIGITAL DOWNCONVERTER
The AD6655 includes a digital processing section that provides
filtering and reduces the output data rate. This digital processing
section includes a numerically controlled oscillator (NCO),
a half-band decimating filter, an FIR filter, and a second coarse
NCO (fADC/8 fixed value) for output frequency translation. Each
of these processing blocks (except the decimating half-band
filter) has control lines that allow it to be independently enabled
and disabled to provide the desired processing function. The
digital downconverter can be configured to output either real data
or complex output data. These blocks can be configured in five
recommended combinations to implement different signal
processing functions.
DOWNCONVERTER MODES
Table 18 details the recommended downconverter modes of
operation in the AD6655.
Table 18. Downconverter Modes
Mode NCO/Filter Output Type
1 Half-band filter only Real
2 Half-band filter and FIR filter Real
3 NCO and half-band filter Complex
4 NCO, half-band filter, and FIR filter Complex
5 NCO, half-band filter, FIR filter, and
fADC/8 NCO
Real
NUMERICALLY CONTROLLED OSCILLATOR (NCO)
Frequency translation is accomplished with an NCO. Each of
the two processing channels shares a common NCO. Amplitude
and phase dither can be enabled on chip to improve the noise and
spurious performance of the NCO. A phase offset word is available
to create a known phase relationship between multiple AD6655s.
Because the decimation filter prevents usage of half the Nyquist
spectrum, a means is needed to translate the sampled input
spectrum into the usable range of the decimation filter. To
achieve this, a 32-bit, fine tuning, complex NCO is provided.
This NCO/mixer allows the input spectrum to be tuned to dc,
where it can be effectively filtered by the subsequent filter
blocks to prevent aliasing.
HALF-BAND DECIMATING FILTER AND FIR FILTER
The goal of the AD6655 digital filter block is to allow the sample
rate to be reduced by a factor of 2 while rejecting aliases that fall
into the band of interest. The half-band filter is designed to operate
as either a low-pass or high-pass filter and to provide greater
than 100 dB of alias protection for 22% of the input rate of the
structure. For an ADC sample rate of 150 MSPS, this provides
a maximum usable bandwidth of 16.5 MHz when using the filter
in real mode (NCO bypassed) or a maximum usable bandwidth
of 33.0 MHz when using the filter in the complex mode (NCO
enabled).
The optional fixed-coefficient FIR filter provides additional
filtering capability to sharpen the half-band roll-off to enhance
the alias protection. It removes the negative frequency images
to avoid aliasing negative frequencies for real outputs.
fADC/8 FIXED-FREQUENCY NCO
A fixed fADC/8 NCO is provided to translate the filtered, decimated
signal from dc to fADC/8 to allow a real output. Figure 68 to
Figure 71 show an example of a 20 MHz input as it is processed
by the blocks of the AD6655.
–50 –24 –14 14 24 50–4 4
0
06709-066
Figure 68. Example AD6655 Real 20 MHz Bandwidth Input Signal Centered at
14 MHz (fADC = 100 MHz)
–50 –38 –28 010 50
–18 –10
06709-067
Figure 69. Example AD6655 20 MHz Bandwidth Input Signal Tuned to DC
Using the NCO (NCO Frequency = 14 MHz)
–50 –38 –28 010 50–18 –10
06709-068
Figure 70. Example AD6655 20 MHz Bandwidth Input Signal with the
Negative Image Filtered by the Half-Band and FIR Filters
–50 0.25 22.512.5 50
06709-069
Figure 71. Example AD6655 20 MHz Bandwidth Input Signal Tuned to
fADC/8 for Real Output
AD6655 Data Sheet
Rev. B | Page 38 of 84
NUMERICALLY CONTROLLED OSCILLATOR (NCO)
FREQUENCY TRANSLATION
This processing stage comprises a digital tuner consisting of
a 32-bit complex numerically controlled oscillator (NCO). The
two channels of the AD6655 share a single NCO. The NCO is
optional and can be bypassed by clearing Bit 0 of Register 0x11D.
This NCO block accepts a real input from the ADC stage and
outputs a frequency translated complex (I and Q) output.
The NCO frequency is programmed in Register 0x11E,
Register 0x11F, Register 0x120, and Register 0x121. These four
8-bit registers make up a 32-bit unsigned frequency programming
word. Frequencies between −CLK/2 and +CLK/2 are represented
using the following frequency words:
0x8000 0000 represents a frequency given by −CLK/2.
0x0000 0000 represents dc (frequency = 0 Hz).
0x7FFF FFFF represents CLK/2 − CLK/232.
Use the following equation to calculate the NCO frequency:
CLK
CLK
f
ffMod
NCO_FREQ ),(
232
where:
NCO_FREQ is a 32-bit twos complement number representing
the NCO frequency register.
f is the desired carrier frequency in hertz (Hz).
fCLK is the AD6655 ADC clock rate in hertz (Hz).
NCO SYNCHRONIZATION
The AD6655 NCOs within a single part or across multiple parts
can be synchronized using the external SYNC input. Bit 3 and
Bit 4 of Register 0x100 allow the NCO to be resynchronized on
every SYNC signal or only on the first SYNC signal after the
register is written. A valid SYNC causes the NCO to restart at
the programmed phase offset value.
PHASE OFFSET
The NCO phase offset register at Address 0x122 and
Address 0x123 adds a programmable offset to the phase
accumulator of the NCO. This 16-bit register is interpreted as
a 16-bit unsigned integer. A 0x00 in this register corresponds
to no offset, and a 0xFFFF corresponds to an offset of 359.995°.
Each bit represents a phase change of 0.005°. This register allows
multiple NCOs to be synchronized to produce outputs with
predictable phase differences. Use the following equation to
calculate the NCO phase offset value:
NCO_PHASE = 216 × PHASE/360
where:
NCO_PHASE is a decimal number equal to the 16-bit binary
number to be programmed at Register 0x122 and Register 0x123.
PHASE is the desired NCO phase in degrees.
NCO AMPLITUDE AND PHASE DITHER
The NCO block contains amplitude and phase dither to improve
the spurious performance. Amplitude dither improves perfor-
mance by randomizing the amplitude quantization errors within
the angular-to-Cartesian conversion of the NCO. This option
reduces spurs at the expense of a slightly raised noise floor. With
amplitude dither enabled, the NCO has an SNR of >93 dB and
an SFDR of >115 dB. With amplitude dither disabled, the SNR
is increased to >96 dB at the cost of SFDR performance, which
is reduced to 100 dB. The NCO amplitude dither is recommended
and is enabled by setting Bit 1 of Register 0x11D.
Data Sheet AD6655
Rev. B | Page 39 of 84
DECIMATING HALF-BAND FILTER AND FIR FILTER
The goal of the AD6655 half-band digital filter is to allow the
sample rate to be reduced by a factor of 2 while rejecting aliases
that fall into the band of interest. This filter is designed to operate
as either a low-pass or a high-pass filter and to provide >100 dB
of alias protection for 11% of the input rate of the structure.
Used in conjunction with the NCO and the FIR filter, the half-
band filter can provide an effective band-pass. For an ADC
sample rate of 150 MSPS, this provides a maximum usable
bandwidth of 33 MHz.
HALF-BAND FILTER COEFFICIENTS
The 19-tap, symmetrical, fixed-coefficient half-band filter has low
power consumption due to its polyphase implementation. Table 19
lists the coefficients of the half-band filter. The normalized
coefficients used in the implementation and the decimal
equivalent value of the coefficients are also listed. Coefficients
not listed in Table 19 are 0s.
Table 19. Fixed Coefficients for Half-Band Filter
Coefficient
Number
Normalized
Coefficient
Decimal Coefficient
(20-Bit)
C0, C18 0.0008049 844
C2, C16 −0.0059023 −6189
C4, C14
0.0239182
25080
C6, C12 −0.0755024 −79170
C8, C10 0.3066864 321584
C9 0.5 524287
HALF-BAND FILTER FEATURES
In the AD6655, the half-band filter cannot be disabled. The
filter can be set for a low-pass or high-pass response. For a high-
pass filter, Bit 1 of Register 0x103 should be set; for a low-pass
response, this bit should be cleared. The low-pass response of the
filter with respect to the normalized output rate is shown in
Figure 72, and the high-pass response is shown in Figure 73.
0
–110
–100
–90
–80
–70
–60
–50
–40
–30
–20
–10
00.1 0.2 0.3 0.4
AMPLITUDE ( dBc)
FRACTION OF INPUT SAMPLE RATE
06709-070
Figure 72. Half-Band Filter Low-Pass Response
0
–110
–100
–90
–80
–70
–60
–50
–40
–30
–20
–10
00.1 0.2 0.3 0.4
AMPLITUDE ( dBc)
FRACTION OF INPUT SAMPLE RATE
06709-071
Figure 73. Half-Band Filter High-Pass Response
The half-band filter has a ripple of 0.000182 dB and a rejection
of 100 dB. For an alias rejection of 100 dB, the alias protected
bandwidth is 11% of the input sample rate. If both the I and the
Q paths are used, a complex bandwidth of 22% of the input rate
is available.
In the event of even Nyquist zone sampling, the half-band filter
can be configured to provide a spectral reversal. Setting Bit 2
high in Address 0x103 enables the spectral reversal feature.
The half-band decimation phase can be selected such that
the half-band filter starts on the first or second sample following
synchronization. This shifts the output from the half-band between
the two input sample clocks. The decimation phase can be set to
0 or 1, using Bit 3 of Register 0x103.
FIXED-COEFFICIENT FIR FILTER
Following the half-band filters is a 66-tap, fixed-coefficient FIR
filter. This filter is useful in providing extra alias protection for
the decimating half-band filter. It is a simple sum-of-products
FIR filter with 66 filter taps and 21-bit fixed coefficients. Note
that this filter does not decimate. The normalized coefficients
used in the implementation and the decimal equivalent value of
the coefficients are listed in Table 20.
The user can either select or bypass this filter, but the FIR filter
can be enabled only when the half-band filter is enabled. Writing
Logic 0 to the enable FIR filter bit (Bit 0) in Register 0x102
bypasses this fixed-coefficient filter. The filter is necessary when
using the final NCO with a real output; bypassing it when using
other configurations results in power savings.
AD6655 Data Sheet
Rev. B | Page 40 of 84
Table 20. FIR Filter Coefficients
Coefficient
Number
Normalized
Coefficient
Decimal Coefficient
(21-Bit)
C0, C65 0.0001826 383
C1, C64 0.0006824 1431
C2, C63
0.0009298
1950
C3, C62 0.0000458 96
C4, C61 −0.0012689 −2661
C5, C60 −0.0008345 −1750
C6, C59 0.0011806 2476
C7, C58
0.0011387
2388
C8, C57 −0.0018439 −3867
C9, C56 −0.0024557 −5150
C10, C55 0.0018063 3788
C11, C54 0.0035825 7513
C12, C53 −0.0021510 −4511
C13, C52
−0.0056810
−11914
C14, C51 0.0017405 3650
C15, C50 0.0078602 16484
C16, C49 −0.0013437 −2818
C17, C48 −0.0110626 −23200
C18, C47 −0.0000229 −48
C19, C46
0.0146618
30748
C20, C45 0.0018959 3976
C21, C44 −0.0195594 −41019
C22, C43 −0.0053153 −11147
C23, C42 0.0255623 53608
C24, C41
0.0104036
21818
C25, C40 −0.0341468 −71611
C26, C39 −0.0192165 −40300
C27, C38 0.0471258 98830
C28, C37 0.0354118 74264
C29, C36 −0.0728111 −152696
C30, C35
−0.0768890
−161248
C31, C34 0.1607208 337056
C32, C33 0.4396725 922060
SYNCHRONIZATION
The AD6655 half-band filters within a single part or across
multiple parts can be synchronized using the external SYNC
input. Bit 5 and Bit 6 of Register 0x100 allow the half-bands to
be resynchronized on every SYNC signal or only on the first
SYNC signal after the register is written. A valid SYNC causes
the half-band filter to restart at the programmed decimation
phase value.
COMBINED FILTER PERFORMANCE
The combined response of the half-band filter and the FIR filter
is shown in Figure 74. The act of bandlimiting the ADC data with
the half-band filter ideally provides a 3 dB improvement in the
SNR at the expense of the sample rate and available bandwidth
of the output data. As a consequence of finite math, additional
quantization noise is added to the system due to truncation in
the NCO and half-band. As a consequence of the digital filter
rejection of out-of-band noise (assuming no quantization in the
filters and with a white noise floor from the ADC), there should
be a 3.16 dB improvement in the ADC SNR. However, the added
quantization lessens improvement to about 2.66 dB.
0
–110
–100
–90
–80
–70
–60
–50
–40
–30
–20
–10
00.1 0.2 0.3 0.4
AMPLITUDE ( dBc)
FRACTION OF INPUT SAMPLE RATE
06709-072
Figure 74. Half-Band Filter and FIR Filter Composite Response
FINAL NCO
The output of the 32-bit fine tuning NCO is complex and
typically centered in frequency around dc. This complex output
is carried through the stages of the half-band and FIR filters to
provide proper antialiasing filtering. The final NCO provides a
means to move this complex output signal away from dc so that
a real output can be provided from the AD6655. The final NCO,
if enabled, translates the output from dc to a frequency equal to
the ADC sampling frequency divided by 8 (fADC/8). This provides
the user a decimated output signal centered at fADC/8 in frequency.
Optionally, this final NCO can be bypassed, and the dc-centered
I and Q values can be output in an interleaved fashion.
Data Sheet AD6655
Rev. B | Page 41 of 84
ADC OVERRANGE AND GAIN CONTROL
In receiver applications, it is desirable to have a mechanism
to reliably determine when the converter is about to be clipped.
The standard overflow indicator provides after-the-fact infor-
mation on the state of the analog input that is of limited usefulness.
Therefore, it is helpful to have a programmable threshold below
full scale that allows time to reduce the gain before the clip actually
occurs. In addition, because input signals can have significant
slew rates, latency of this function is of major concern. Highly
pipelined converters can have significant latency. A good compro-
mise is to use the output bits from the first stage of the ADC for
this function. Latency for these output bits is very low, and overall
resolution is not highly significant. Peak input signals are typically
between full scale and 6 dB to 10 dB below full scale. A 3-bit or
4-bit output provides adequate range and resolution for this
function.
Using the SPI port, the user can provide a threshold above which
an overrange output is active. As long as the signal is below that
threshold, the output should remain low. The fast detect outputs
can also be programmed via the SPI port so that one of the pins
functions as a traditional overrange pin for customers who
currently use this feature. In this mode, all 14 bits of the converter
are examined in the traditional manner, and the output is high
for the condition normally defined as overflow. In either mode,
the magnitude of the data is considered in the calculation of the
condition (but the sign of the data is not considered). The threshold
detection responds identically to positive and negative signals
outside the desired range (magnitude).
FAST DETECT OVERVIEW
The AD6655 contains circuitry to facilitate fast overrange
detection, allowing very flexible external gain control imple-
mentations. Each ADC has four fast detect (FD) output pins
that are used to output information about the current state of
the ADC input level. The function of these pins is programmable
via the fast detect mode select bits and the fast detect enable bit
in Register 0x104, allowing range information to be output from
several points in the internal data path. These output pins can
also be set up to indicate the presence of overrange or underrange
conditions, according to programmable threshold levels. Table 21
shows the six configurations available for the fast detect pins.
Table 21. Fast Detect Mode Select Bits Settings
Fast Detect
Mode Select bits
(Register 0x104[3:1])
Information Presented on
Fast Detect (FD) Pins of Each ADC1, 2
FD[3] FD[2] FD[1] FD[0]
000 ADC fast magnitude (see Table 22)
001 ADC fast magnitude
(see Table 23)
OR
010 ADC fast
magnitude
(see Table 24)
OR F_LT
011 ADC fast
magnitude
(see Table 24)
C_UT F_LT
100 OR C_UT F_UT F_LT
101 OR F_UT IG DG
1 The fast detect pins are FD0A/FD0B to FD3A/FD3B for the CMOS mode
configuration and FD0+/FD0− to FD3+/FD3− for the LVDS mode
configuration.
2 See the ADC Overrange (OR) and Gain Switching sections for more
information about OR, C_UT, F_UT, F_LT, IG, and DG.
ADC FAST MAGNITUDE
When the fast detect output pins are configured to output the
ADC fast magnitude (that is, when the fast detect mode select
bits are set to 0b000), the information presented is the ADC
level from an early converter stage with a latency of only two
clock cycles in CMOS output modes. In LVDS output mode,
the fast detect bits have a latency of six cycles in all fast detect
modes. Using the fast detect output pins in this configuration
provides the earliest possible level indication information. Because
this information is provided early in the datapath, there is signifi-
cant uncertainty in the level indicated. The nominal levels, along
with the uncertainty indicated by the ADC fast magnitude, are
shown in Table 22. Because the DCO is at one-half the sample
rate, the user can obtain all the fast detect information by sampling
the fast detect outputs on both the rising and falling edge of
DCO (see Figure 2 for timing information).
Table 22. ADC Fast Magnitude Nominal Levels
with Fast Detect Mode Select Bits = 000
ADC Fast
Magnitude on
FD[3:0] Pins
Nominal Input
Magnitude
Below FS (dB)
Nominal Input
Magnitude
Uncertainty (dB)
0000 <−24 Minimum to −18.07
0001 −24 to −14.5 −30.14 to −12.04
0010 −14.5 to −10 −18.07 to −8.52
0011 −10 to −7 −12.04 to −6.02
0100 −7 to −5 −8.52 to −4.08
0101 −5 to −3.25 −6.02 to −2.5
0110 −3.25 to −1.8 −4.08 to −1.16
0111 −1.8 to −0.56 −2.5 to FS
1000 −0.56 to 0 −1.16 to 0
AD6655 Data Sheet
Rev. B | Page 42 of 84
When the fast detect mode select bits are set to 0b001, 0b010,
or 0b011, a subset of the fast detect output pins are available.
In these modes, the fast detect output pins have a latency of six
clock cycles, and the greater of the two input samples is output
at the DCO rate. Table 23 shows the corresponding ADC input
levels when the fast detect mode select bits are set to 0b001 (that
is, when the ADC fast magnitude is presented on the FD[3:1] pins).
Table 23. ADC Fast Magnitude Nominal Levels
with Fast Detect Mode Select Bits = 001
ADC Fast
Magitude on
FD[2:0] Pins
Nominal Input
Magnitude
Below FS (dB)
Nominal Input
Magnitude
Uncertainty (dB)
000
<−24
Minimum to −18.07
001 −24 to −14.5 −30.14 to −12.04
010 −14.5 to −10 −18.07 to −8.52
011 −10 to −7 −12.04 to −6.02
100 −7 to −5 −8.52 to −4.08
101 −5 to −3.25 −6.02 to −2.5
110 −3.25 to −1.8 −4.08 to −1.16
111 −1.8 to 0 −2.5 to 0
When the fast detect mode select bits are set to 0b010 or 0b011
(that is, when ADC fast magnitude is presented on the FD[2:1]
pins), the LSB is not provided. The input ranges for this mode
are shown in Table 24.
Table 24. ADC Fast Magnitude Nominal Levels
with Fast Detect Mode Select Bits = 010 or 011
ADC Fast
Magitude on
FD[2:1] Pins
Nominal Input
Magnitude
Below FS (dB)
Nominal Input
Magnitude
Uncertainty (dB)
00 <−14.5 Minimum to −12.04
01 −14.5 to −7 −18.07 to −6.02
10 −7 to −3.25 −8.52 to −2.5
11 −3.25 to 0 −4.08 to 0
ADC OVERRANGE (OR)
The ADC overrange indicator is asserted when an overrange is
detected on the input of the ADC. The overrange condition is
determined at the output of the ADC pipeline and, therefore, is
subject to a latency of 12 ADC clock cycles. An overrange at the
input is indicated by this bit 12 clock cycles after it occurs.
GAIN SWITCHING
The AD6655 includes circuitry that is useful in applications
either where large dynamic ranges exist or where gain ranging
converters are employed. This circuitry allows digital thresholds
to be set such that an upper threshold and a lower threshold can
be programmed. Fast detect mode select bits = 010 through fast
detect mode select bits = 101 support various combinations of
the gain switching options.
One such use is to detect when an ADC is about to reach full
scale with a particular input condition. The result is to provide
an indicator that can be used to quickly insert an attenuator that
prevents ADC overdrive.
Coarse Upper Threshold (C_UT)
The coarse upper threshold indicator is asserted if the ADC fast
magnitude input level is greater than the level programmed in
the coarse upper threshold register (Address 0x105[2:0]). This
value is compared with the ADC Fast Magnitude Bits[2:0]. The
coarse upper threshold output is output two clock cycles after
the level is exceeded at the input and, therefore, provides a fast
indication of the input signal level. The coarse upper threshold
levels are shown in Table 25. This indicator remains asserted for
a minimum of two ADC clock cycles or until the signal drops
below the threshold level.
Table 25. Coarse Upper Threshold Levels
Coarse Upper Threshold
Register[2:0]
C_UT Is Active When Signal
Magnitude Below FS
Is Greater Than (dB)
000 <−24
001 −24
010
−14.5
011 −10
100 −7
101 −5
110 −3.25
111
−1.8
Fine Upper Threshold (F_UT)
The fine upper threshold indicator is asserted if the input
magnitude exceeds the value programmed in the fine upper
threshold register located in Register 0x106 and Register 0x107.
The 13-bit threshold register is compared with the signal magni-
tude at the output of the ADC. This comparison is subject to
the ADC clock latency but is accurate in terms of converter
resolution. The fine upper threshold magnitude is defined by
the following equation:
dBFS = 20 log(Threshold Magnitude/213)
Fine Lower Threshold (F_LT)
The fine lower threshold indicator is asserted if the input magni-
tude is less than the value programmed in the fine lower threshold
register located at Register 0x108 and Register 0x109. The fine
lower threshold register is a 13-bit register that is compared with
the signal magnitude at the output of the ADC. This comparison
is subject to ADC clock latency but is accurate in terms of
converter resolution. The fine lower threshold magnitude
is defined by the following equation:
dBFS = 20 log(Threshold Magnitude/213)
The operation of the fine upper threshold and fine lower
threshold indicators is shown in Figure 75.
Data Sheet AD6655
Rev. B | Page 43 of 84
Increment Gain (IG) and Decrement Gain (DG)
The increment gain and decrement gain indicators are intended
to be used together to provide information to enable external
gain control. The decrement gain indicator works in conjunction
with the coarse upper threshold bits, asserting when the input
magnitude is greater than the 3-bit value in the coarse upper
threshold register (Address 0x105). The increment gain indicator,
similarly, corresponds to the fine lower threshold bits except
that it is asserted only if the input magnitude is less than the
value programmed in the fine lower threshold register after the
dwell time elapses. The dwell time is set by the 16-bit dwell time
value located at Address 0x10A and Address 0x10B and is set in
units of ADC input clock cycles ranging from 1 to 65,535. The
fine lower threshold register is a 13-bit register that is compared
with the magnitude at the output of the ADC. This comparison
is subject to the ADC clock latency but allows a finer, more
accurate comparison. The fine upper threshold magnitude is
defined by the following equation:
dBFS = 20 log(Threshold Magnitude/213)
The decrement gain output works from the ADC fast detect
output pins, providing a fast indication of potential overrange
conditions. The increment gain uses the comparison at the
output of the ADC, requiring the input magnitude to remain
below an accurate, programmable level for a predefined period
before signaling external circuitry to increase the gain.
The operation of the increment gain output and decrement gain
output is shown graphically in Figure 75.
UPPE R THRESHOL D ( COARSE OR F INE)
FINE LOWER THRESHOLD
IG
DG
F_LT
C_UT OR F_UT*
DWELL TIME
TIMER RESET BY
RIS E ABOVE F_L T
TIMER COMPLET ES BEFO RE
SIGNAL RISES ABOVE F_LT
NOTE: OUT P UTS FO LLOW THE INSTANTE OUS S IG NAL L E V E L AND NO T THE E NV E LO P E BUT ARE GUARANT E E D ACTIV E FO R A M INI M UM OF 2 ADC CLO CK CY CLES.
*C_UT AND F_UT DIF FER ONL Y IN ACCURACY AND L ATENCY .
DWELL TIME
06709-073
Figure 75. Threshold Settings for C_UT, F_UT, F_LT, DG, and IG
AD6655 Data Sheet
Rev. B | Page 44 of 84
SIGNAL MONITOR
The signal monitor block provides additional information
about the signal being digitized by the ADC. The signal monitor
computes the rms input magnitude, the peak magnitude, and/or
the number of samples by which the magnitude exceeds a
particular threshold. Together, these functions can be used to
gain insight into the signal characteristics and to estimate the
peak/average ratio or even the shape of the complementary
cumulative distribution function (CCDF) curve of the input
signal. This information can be used to drive an AGC loop to
optimize the range of the ADC in the presence of real-world
signals.
The signal monitor result values can be obtained from the part by
reading back internal registers at Address 0x116 to Address 0x11B,
using the SPI port or the signal monitor SPORT output. The output
contents of the SPI-accessible signal monitor registers are set via
the two signal monitor mode bits of the signal monitor control
register (Address 0x112). Both ADC channels must be configured
for the same signal monitor mode. Separate SPI-accessible, 20-bit
signal monitor result (SMR) registers are provided for each ADC
channel. Any combination of the signal monitor functions can
also be output to the user via the serial SPORT interface. These
outputs are enabled using the peak detector output enable, the
rms magnitude output enable, and the threshold crossing output
enable bits in the signal monitor SPORT control register
(Address 0x1111).
For each signal monitor measurement, a programmable signal
monitor period register (SMPR) controls the duration of the
measurement. This time period is programmed as the number
of input clock cycles in a 24-bit signal monitor period register
located at Address 0x113, Address 0x114, and Address 0x115.
This register can be programmed with a period from 128 samples
to 16.78 (224) million samples.
Because the dc offset of the ADC can be significantly larger
than the signal of interest (affecting the results from the signal
monitor), a dc correction circuit is included as part of the signal
monitor block to null the dc offset before measuring the power.
PEAK DETECTOR MODE
The magnitude of the input port signal is monitored over a
programmable time period (determined by SMPR) to give the
peak value detected. This function is enabled by programming a
Logic 1 in the signal monitor mode bits of the signal monitor
control register or by setting the peak detector output enable bit
in the signal monitor SPORT control register. The 24-bit SMPR
must be programmed before activating this mode.
After enabling this mode, the value in the SMPR is loaded into a
monitor period timer, and the countdown is started. The
magnitude of the input signal is compared with the value in the
internal peak level holding register (not accessible to the user),
and the greater of the two is updated as the current peak level.
The initial value of the peak level holding register is set to the
current ADC input signal magnitude. This comparison continues
until the monitor period timer reaches a count of 1.
When the monitor period timer reaches a count of 1, the 13-bit
peak level value is transferred to the signal monitor holding
register (not accessible to the user), which can be read through
the SPI port or output through the SPORT serial interface. The
monitor period timer is reloaded with the value in the SMPR,
and the countdown is restarted. In addition, the magnitude of
the first input sample is updated in the peak level holding
register, and the comparison and update procedure, as
explained previously, continues.
Figure 76 is a block diagram of the peak detector logic. The
SMR register contains the absolute magnitude of the peak
detected by the peak detector logic.
POWER MONITOR
HOLDING
REGISTER
MAGNITUDE
STORAGE
REGISTER
COMPARE
A>B
TO
MEMORY
MAP
FROM
MEMORY
MAP
FROM
INPUT
PORTS
LOAD
CLEAR
LOAD LOAD
TO
INTERRUPT
CONTROLLER
IS COUNT = 1?
DOWN
COUNTER
POWER MONITOR
PERIOD REGISTER
06709-074
Figure 76. ADC Input Peak Detector Block Diagram
RMS/MS MAGNITUDE MODE
In this mode, the root-mean-square (rms) or mean-square (ms)
magnitude of the input port signal is integrated (by adding an
accumulator) over a programmable time period (determined by
SMPR) to give the rms or ms magnitude of the input signal.
This mode is set by programming Logic 0 in the signal monitor
mode bits of the signal monitor control register or by setting the
rms magnitude output enable bit in the signal monitor SPORT
control register. The 24-bit SMPR, representing the period over
which integration is performed, must be programmed before
activating this mode.
After enabling the rms/ms magnitude mode, the value in the
SMPR is loaded into a monitor period timer, and the countdown
is started immediately. Each input sample is converted to floating-
point format and squared. It is then converted to 11-bit, fixed-
point format and added to the contents of the 24-bit accumulator.
The integration continues until the monitor period timer
reaches a count of 1.
When the monitor period timer reaches a count of 1, the square
root of the value in the accumulator is taken and transferred
(after some formatting) to the signal monitor holding register,
which can be read through the SPI port or output through the
SPORT serial port. The monitor period timer is reloaded with
the value in the SMPR, and the countdown is restarted.
Data Sheet AD6655
Rev. B | Page 45 of 84
In addition, the first input sample signal power is updated in
the accumulator, and the accumulation continues with the
subsequent input samples. Figure 77 illustrates the rms
magnitude monitoring logic.
POWER MONITOR
HOLDING
REGISTER
ACCUMULATOR
FROM
MEMORY
MAP
FROM
INPUT
PORTS
LOAD
CLEAR LOAD
IS COUNT = 1?
DOWN
COUNTER
POWER MONITOR
PERIOD REGISTER
TO
MEMORY
MAP
TO
INTERRUPT
CONTROLLER
06709-075
Figure 77. ADC Input RMS Magnitude Monitoring Block Diagram
For rms magnitude mode, the value in the signal monitor result
(SMR) register is a 20-bit fixed-point number. The following
equation can be used to determine the rms magnitude in dBFS
from the MAG value in the register. Note that if the signal
monitor period (SMP) is a power of 2, the second term in the
equation becomes 0.
RMS Magnitude = 20 log
[ ]
/
)(log20 2
2
log10
2SMPceil
SMPMAG
For ms magnitude mode, the value in the SMR is a 20-bit fixed-
point number. The following equation can be used to determine
the ms magnitude in dBFS from the MAG value in the register.
Note that if the SMP is a power of 2, the second term in the
equation becomes 0.
MS Magnitude = 10 log
[ ]
/
)(log20 2
2
log10
2SMPceil
SMPMAG
THRESHOLD CROSSING MODE
In the threshold crossing mode of operation, the magnitude of
the input port signal is monitored over a programmable time
period (given by SMPR) to count the number of times it crosses
a certain programmable threshold value. This mode is set by
programming Logic 1x (where x is a don’t care bit) in the signal
monitor mode bits of the signal monitor control register or by
setting the threshold crossing output enable bit in the signal
monitor SPORT control register. Before activating this mode,
the user needs to program the 24-bit SMPR and the 13-bit
upper threshold register for each individual input port. The
same upper threshold register is used for both signal monitoring
and gain control (see the ADC Overrange and Gain Control
section).
After entering this mode, the value in the SMPR is loaded into a
monitor period timer, and the countdown is started. The
magnitude of the input signal is compared with the upper
threshold register (programmed previously) on each input clock
cycle. If the input signal has a magnitude greater than the upper
threshold register, the internal count register is incremented by 1.
The initial value of the internal count register is set to 0. This
comparison and incrementing of the internal count register
continues until the monitor period timer reaches a count of 1.
When the monitor period timer reaches a count of 1, the value
in the internal count register is transferred to the signal monitor
holding register, which can be read through the SPI port or
output through the SPORT serial port.
The monitor period timer is reloaded with the value in the
SMPR register, and the countdown is restarted. The internal
count register is also cleared to a value of 0. Figure 78 illustrates
the threshold crossing logic. The value in the SMR register is
the number of samples that have a magnitude greater than the
threshold register.
POWER MONITOR
HOLDING
REGISTER
COMPARE
A>B
UPPER
THRESHOLD
REGISTER
COMPARE
A>B
FROM
MEMORY
MAP
FROM
MEMORY
MAP
FROM
INPUT
PORTS
LOAD
CLEAR LOAD
IS COUNT = 1?
DOWN
COUNTER
POWER MONITOR
PERIOD REGISTER
B
A
TO
MEMORY
MAP
TO
INTERRUPT
CONTROLLER
06709-076
Figure 78. ADC Input Threshold Crossing Block Diagram
ADDITIONAL CONTROL BITS
For additional flexibility in the signal monitoring process, two
control bits are provided in the signal monitor control register.
They are the signal monitor enable bit and the complex power
calculation mode enable bit.
Signal Monitor Enable Bit
The signal monitor enable bit, located in Bit 0 of Register 0x112,
enables operation of the signal monitor block. If the signal
monitor function is not needed in a particular application, this
bit should be cleared to conserve power.
Complex Power Calculation Mode Enable Bit
When this bit is set, the part assumes that Channel A is digitizing
the I data and Channel B is digitizing the Q data for a complex
input signal (or vice versa). In this mode, the power reported is
equal to
22 QI +
This result is presented in the Signal Monitor DC Value Channel A
register if the signal monitor mode bits are set to 00. The Signal
Monitor DC Value Channel B register continues to compute the
Channel B value.
DC CORRECTION
Because the dc offset of the ADC may be significantly larger
than the signal being measured, a dc correction circuit is included
to null the dc offset before measuring the power. The dc correction
circuit can also be switched into the main signal path, but this
may not be appropriate if the ADC is digitizing a time-varying
signal with significant dc content, such as GSM.
AD6655 Data Sheet
Rev. B | Page 46 of 84
DC Correction Bandwidth
The dc correction circuit is a high-pass filter with a programmable
bandwidth (ranging between 0.15 Hz and 1.2 kHz at 125 MSPS).
The bandwidth is controlled by writing the 4-bit dc correction
control register located at Register 0x10C, Bits[5:2]. The following
equation can be used to compute the bandwidth value for the dc
correction circuit:
π×
×= //
2
2__ 14kCLK
f
BWCorrDC
where:
k is the 4-bit value programmed in Bits[5:2] of Register 0x10C
(values between 0 and 13 are valid for k; programming 14 or 15
provides the same result as programming 13).
fCLK is the AD6655 ADC sample rate in hertz (Hz).
DC Correction Readback
The current dc correction value can be read back in Register 0x10D
and Register 0x10E for Channel A and Register 0x10F and
Register 0x110 for Channel B. The dc correction value is a
14-bit value that can span the entire input range of the ADC.
DC Correction Freeze
Setting Bit 6 of Register 0x10C freezes the DC correction at its
current state and continues to use the last updated value as the
dc correction value. Clearing this bit restarts dc correction and
adds the currently calculated value to the data.
DC Correction Enable Bits
Setting Bit 0 of Register 0x10C enables dc correction for use in
the signal monitor calculations. The calculated dc correction value
can be added to the output data signal path by setting Bit 1 of
Register 0x10C.
SIGNAL MONITOR SPORT OUTPUT
The SPORT is a serial interface with three output pins: the SMI
SCLK (SPORT clock), SMI SDFS (SPORT frame sync), and SMI
SDO (SPORT data output). The SPORT is the master and drives
all three SPORT output pins on the chip.
SMI SCLK
The data and frame sync are driven on the positive edge of the
SMI SCLK. The SMI SCLK has three possible baud rates: 1/2, 1/4,
or 1/8 the ADC clock rate, based on the SPORT controls. The
SMI SCLK can also be gated off when not sending any data, based
on the SPORT SMI SCLK sleep bit. Using this bit to disable the
SMI SCLK when it is not needed can reduce any coupling errors
back into the signal path, if these prove to be a problem in the
system. Doing so, however, has the disadvantage of spreading
the frequency content of the clock. If desired the SMI SCLK
can be left running to ease frequency planning.
SMI SDFS
The SMI SDFS is the serial data frame sync, and it defines the
start of a frame. One SPORT frame includes data from both
datapaths. The data from Datapath A is sent just after the frame
sync, followed by data from Datapath B.
SMI SDO
The SMI SDO is the serial data output of the block. The data is
sent MSB first on the next positive edge after the SMI SDFS.
Each data output block includes one or more of rms magnitude,
peak level, and threshold crossing values from each datapath in
the stated order. If enabled, the data is sent, rms first, followed
by peak and threshold, as shown in Figure 79.
20 CYCLE S 16 CYCLE S16 CYCLE S 20 CYCLE S 16 CYCLES 16 CYCL E S
SMI SDFS
MSB MSB
RMS/MS CH A PK CH A PK CH B THR CH B
RMS/MS CH B RMS/MS CH A
LSB LSB
THR CH A
SMI SDO
SMI SCLK
GAT E D, BASE D ON CO NTRO L
06709-077
Figure 79. Signal Monitor SPORT Output Timing (RMS, Peak, and Threshold Enabled)
20 CYCL E S 16 CYCLE S 20 CYCLES 16 CYCL E S
SMI SCLK
SMI SDFS
SMI SDO MSB MSBRMS/MS CH A RMS/MS CH A
LSB T HR CH A RMS/MS CH B LSB T HR CH B
GATED, BAS E D ON CO NTRO L
06709-078
Figure 80. Signal Monitor SPORT Output Timing (RMS and Threshold Enabled)
Data Sheet AD6655
Rev. B | Page 47 of 84
CHANNEL/CHIP SYNCHRONIZATION
The AD6655 has a SYNC input that allows the user flexible
synchronization options for synchronizing the internal blocks.
The sync feature is useful for guaranteeing synchronized operation
across multiple ADCs. The input clock divider, NCO, half-band
filters, and signal monitor block can be synchronized using the
SYNC input. Each of these blocks, except for the signal monitor,
can be enabled to synchronize on a single occurrence of the
SYNC signal or on every occurrence.
The SYNC input is internally synchronized to the sample clock.
However, to ensure that there is no timing uncertainty between
multiple parts, the SYNC input signal should be synchronized
to the input clock signal. The SYNC input should be driven
using a single-ended CMOS type signal.
AD6655 Data Sheet
Rev. B | Page 48 of 84
SERIAL PORT INTERFACE (SPI)
The AD6655 serial port interface (SPI) allows the user to configure
the converter for specific functions or operations through a
structured register space provided inside the ADC. The SPI
gives the user added flexibility and customization, depending on
the application. Addresses are accessed via the serial port and
can be written to or read from via the port. Memory is organized
into bytes that can be further divided into fields. These fields are
documented in the Memory Map section. For detailed operational
information, see Application Note AN-877, Interfacing to High
Speed ADCs via SPI.
CONFIGURATION USING THE SPI
Three pins define the SPI of this ADC: the SCLK/DFS pin, the
SDIO/DCS pin, and the CSB pin (see Table 26). The SCLK/DFS
(serial clock) pin is used to synchronize the read and write data
presented from/to the ADC. The SDIO/DCS (serial data input/
output) pin is a dual-purpose pin that allows data to be sent and
read from the internal ADC memory map registers. The CSB
(chip select bar) pin is an active-low control that enables or disables
the read and write cycles.
Table 26. Serial Port Interface Pins
Pin Function
SCLK Serial Clock. The serial shift clock input, which is used to
synchronize serial interface reads and writes.
SDIO
Serial Data Input/Output. A dual-purpose pin that
typically serves as an input or an output, depending on
the instruction being sent and the relative position in the
timing frame.
CSB Chip Select Bar. An active-low control that gates the read
and write cycles.
The falling edge of the CSB, in conjunction with the rising edge
of the SCLK, determines the start of the framing. An example of
the serial timing and its definitions can be found in Figure 81
and Table 9.
Other modes involving the CSB are available. The CSB can be
held low indefinitely, which permanently enables the device;
this is called streaming. The CSB can stall high between bytes
to allow for additional external timing. When CSB is tied high,
SPI functions are placed in a high impedance mode. This mode
turns on any SPI pin secondary functions.
During an instruction phase, a 16-bit instruction is transmitted.
Data follows the instruction phase, and its length is determined
by the W0 bit and the W1 bit.
All data is composed of 8-bit words. The first bit of each individual
byte of serial data indicates whether a read command or a write
command is issued. This allows the serial data input/output
(SDIO) pin to change direction from an input to an output.
In addition to word length, the instruction phase determines
whether the serial frame is a read or write operation, allowing
the serial port to be used both to program the chip and to read
the contents of the on-chip memory. If the instruction is a readback
operation, performing a readback causes the serial data input/
output (SDIO) pin to change direction from an input to an output
at the appropriate point in the serial frame.
Data can be sent in MSB-first mode or in LSB-first mode. MSB
first is the default on power-up and can be changed via the SPI
port configuration register. For more information about this
and other features, see Application Note AN-877, Interfacing to
High Speed ADCs via SPI at www.analog.com.
HARDWARE INTERFACE
The pins described in Table 26 comprise the physical interface
between the user programming device and the serial port of the
AD6655. The SCLK pin and the CSB pin function as inputs
when using the SPI interface. The SDIO pin is bidirectional,
functioning as an input during write phases and as an output
during readback.
The SPI interface is flexible enough to be controlled by either
FPGAs or microcontrollers. One method for SPI configuration
is described in detail in Application Note AN-812, Microcontroller-
Based Serial Port Interface (SPI) Boot Circuit.
The SPI port should not be active during periods when the full
dynamic performance of the converter is required. Because the
SCLK signal, the CSB signal, and the SDIO signal are typically
asynchronous to the ADC clock, noise from these signals can
degrade converter performance. If the on-board SPI bus is used for
other devices, it may be necessary to provide buffers between
this bus and the AD6655 to prevent these signals from transi-
tioning at the converter inputs during critical sampling periods.
Some pins serve a dual function when the SPI interface is not
being used. When the pins are strapped to AVDD or ground
during device power-on, they are associated with a specific
function. The Digital Outputs section describes the strappable
functions supported on the AD6655.
Data Sheet AD6655
Rev. B | Page 49 of 84
CONFIGURATION WITHOUT THE SPI
In applications that do not interface to the SPI control registers,
the SDIO/DCS pin, the SCLK/DFS pin, the SMI SDO/OEB pin,
and the SMI SCLK/PDWN pin serve as standalone CMOS-
compatible control pins. When the device is powered up, it is
assumed that the user intends to use the pins as static control
lines for the duty cycle stabilizer, output data format, output
enable, and power-down feature control. In this mode, the CSB
chip select should be connected to AVDD, which disables the
serial port interface.
Table 27. Mode Selection
Pin
External
Voltage Configuration
SDIO/DCS AVDD (default) Duty cycle stabilizer
enabled
AGND Duty cycle stabilizer
disabled
SCLK/DFS AVDD Twos complement
enabled
AGND (default)
Offset binary enabled
SMI SDO/OEB AVDD Outputs in high
impedance
AGND (default) Outputs enabled
SMI SCLK/PDWN AVDD Chip in power-down or
standby
AGND (default) Normal operation
SPI ACCESSIBLE FEATURES
Table 28 provides a brief description of the general features that
are accessible via the SPI. These features are described in detail
in Application Note AN-877, Interfacing to High Speed ADCs via
SPI (see www.analog.com). The AD6655 part-specific features
are described in the Memory Map Register Description section.
Table 28. Features Accessible Using the SPI
Feature Name Description
Mode Allows the user to set either power-down
mode or standby mode
Clock
Allows the user to access the DCS via the SPI
Offset Allows the user to digitally adjust the
converter offset
Test I/O Allows the user to set test modes to have
known data on output bits
Output Mode Allows the user to set up outputs
Output Phase Allows the user to set the output clock polarity
Output Delay Allows the user to vary the DCO delay
VREF Allows the user to set the reference voltage
DON’ T CARE
DON’ T CAREDON’ T CARE
DON’ T CARE
SDIO
SCLK
CSB
t
S
t
DH
t
CLK
t
DS
t
H
R/W W1 W0 A12 A11 A10 A9 A8 A7 D5 D4 D3 D2 D1 D0
t
LOW
t
HIGH
06709-079
Figure 81. Serial Port Interface Timing Diagram
AD6655 Data Sheet
Rev. B | Page 50 of 84
MEMORY MAP
READING THE MEMORY MAP REGISTER TABLE
Each row in the memory map register table has eight bit locations.
The memory map is roughly divided into four sections: the chip
configuration registers (Address 0x00 to Address 0x02); the
channel index and transfer registers (Address 0x05 and
Address 0xFF); the ADC functions registers, including setup,
control, and test (Address 0x08 to Address 0x18); and the digital
feature control registers (Address 0x100 to Address 0x123).
The memory map register table (see Table 29) documents the
default hexadecimal value for each hexadecimal address shown.
The column with the heading Bit 7 (MSB) is the start of the
default hexadecimal value given. For example, Address 0x18, the
VREF select register, has a hexadecimal default value of 0xC0. This
means that Bit 7 = 1, Bit 6 = 1, and the remaining bits are 0s. This
setting is the default reference selection setting. The default value
uses a 2.0 V p-p reference. For more information on this function
and others, see Application Note AN-877, Interfacing to High Speed
ADCs via SPI. This document details the functions controlled by
Register 0x00 to Register 0xFF. The remaining registers, from
Register 0x100 to Register 0x123, are documented in the Memory
Map Register Description section.
Open Locations
All address and bit locations that are not included in Table 29
are not currently supported for this device. Unused bits of a
valid address location should be written with 0s. Writing to these
locations is required only when part of an address location is
open (for example, Address 0x18). If the entire address location
is open (for example, Address 0x13), this address location should
not be written.
Default Values
After the AD6655 is reset, critical registers are loaded with
default values. The default values for the registers are given in
the memory map register table, Table 29.
Logic Levels
An explanation of logic level terminology follows:
• “Bit is set” is synonymous with “bit is set to Logic 1” or
“writing Logic 1 for the bit.”
• “Clear a bit” is synonymous with “bit is set to Logic 0” or
“writing Logic 0 for the bit.”
Transfer Register Map
Address 0x08 to Address 0x18 and Address 0x11E to
Address 0x123 are shadowed. Writes to these addresses do
not affect part operation until a transfer command is issued by
writing 0x01 to Address 0xFF, setting the transfer bit. This allows
these registers to be updated internally and simultaneously when
the transfer bit is set. The internal update takes place when the
transfer bit is set, and the bit autoclears.
Channel-Specific Registers
Some channel setup functions, such as the signal monitor
thresholds, can be programmed differently for each channel.
In these cases, channel address locations are internally duplicated
for each channel. These registers and bits are designated in Table 29
as local. These local registers and bits can be accessed by setting
the appropriate Channel A or Channel B bits in Register 0x05. If
both bits are set, the subsequent write affects the registers of both
channels. In a read cycle, only Channel A or Channel B should
be set to read one of the two registers. If both bits are set during
an SPI read cycle, the part returns the value for Channel A.
Registers and bits designated as global in Table 29 affect the entire
part or the channel features where independent settings are not
allowed between channels. The settings in Register 0x05 do not
affect the global registers and bits.
Data Sheet AD6655
Rev. B | Page 51 of 84
MEMORY MAP REGISTER TABLE
All address and bit locations that are not included in Table 29 are not currently supported for this device.
Table 29. Memory Map Registers
Addr.
(Hex)
Register
Name
Bit 7
(MSB) Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1
Bit 0
(LSB)
Default
Value
(Hex)
Default
Notes/
Comments
Chip Configuration Registers
0x00 SPI Port
Configuration
(Global)
0 LSB first Soft reset 1 1 Soft
reset
LSB first 0 0x18 The nibbles
are mirrored
so that
LSB-first or
MSB-first
mode
registers
correctly,
regardless of
shift mode
0x01 Chip ID
(Global)
8-bit Chip ID[7:0]
(AD6655 = 0x0D)
(default)
0x0D Default is
unique chip
ID, different
for each
device; this is
a read-only
register
0x02 Chip Grade
(Global)
Open Open Speed Grade ID[4:3]
00 = 150 MSPS
01 = 125 MSPS
10 = 105 MSPS
11 = 80 MSPS
Open Open Open Open Speed grade
ID used to
differentiate
devices; this
is a read-only
register
Channel Index and Transfer Registers
0x05 Channel
Index
Open Open Open Open Open Open Data
Channel B
(default)
Data
Channel A
(default)
0x03 Bits are set to
determine
which device
on chip
receives the
next write
command;
applies to
local registers
0xFF Transfer Open Open Open Open Open Open Open Transfer 0x00 Synchronously
transfers data
from the
master shift
register to
the slave
ADC Function Registers
0x08 Power Modes Open Open External
power-
down pin
function
(global)
0 = pdwn
1 = stndby
Open Open Open Internal power-down
mode (local)
00 = normal operation
01 = full power-down
10 = standby
11 = normal operation
0x00 Determines
various
generic
modes of chip
operation
0x09 Global Clock
(Global)
Open Open Open Open Open Open Open Duty cycle
stabilize
(default)
0x01
0x0B Clock Divide
(Global)
Open Open Open Open Open Clock divide ratio
000 = divide by 1
001 = divide by 2
010 = divide by 3
011 = divide by 4
100 = divide by 5
101 = divide by 6
110 = divide by 7
111 = divide by 8
0x00 Clock divide
values other
than 000
automatically
activate
duty cycle
stabilization
AD6655 Data Sheet
Rev. B | Page 52 of 84
Addr.
(Hex)
Register
Name
Bit 7
(MSB) Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1
Bit 0
(LSB)
Default
Value
(Hex)
Default
Notes/
Comments
0x0D Test Mode
(Local)
Open Open Open Open Open Output test mode
000 = off (default)
001 = midscale short
010 = positive FS
011 = negative FS
Others = not supported
0x00 When
enabled, the
test data is
placed on the
output pins
in place of
ADC output
data
0x10 Offset Adjust
(Local)
Open Open Offset adjust in LSBs from +31 to -32 (twos complement format) 0x00
0x14 Output Mode Drive
strength
0 V to 3.3
V CMOS or
ANSI
LVDS;
1 V to 1.8
V CMOS or
reduced
LVDS
(global)
Output
type
0 = CMOS
1 = LVDS
(global)
Interleaved
CMOS
(global)
Output
enable
bar (local)
Open Output
invert
(local)
00 = offset binary
01 = twos complement
01 = gray code
11 = offset binary
(local)
0x00 Configures
the outputs
and the
format of
the data
0x16 Clock Phase
Control
(Global)
Invert
DCO clock
Open Open Open Open Input clock divider phase adjust
000 = no delay
001 = 1 input clock cycle
010 = 2 input clock cycles
011 = 3 input clock cycles
100 = 4 input clock cycles
101 = 5 input clock cycles
110 = 6 input clock cycles
111 = 7 input clock cycles
0x00 Allows
selection of
clock delays
into the input
divider
0x17 DCO Output
Delay
(Global)
Open Open Open DCO clock delay
(delay = 2500 ps × register value/31)
00000 = 0 ps
00001 = 81 ps
00010 = 161 ps
…
11110 = 2419 ps
11111 = 2500 ps
0x00
0x18 VREF Select
(Global)
Reference voltage
selection
00 = 1.25 V p-p
01 = 1.5 V p-p
10 = 1.75 V p-p
11 = 2.0 V p-p
(default)
Open Open Open Open Open Open 0xC0
Digital Feature Control Registers
0x100 Sync Control
(Global)
Signal
monitor
sync
enable
Half-band
next sync
only
Half-band
sync
enable
NCO32
next sync
only
NCO32
sync
enable
Clock
divider
next
sync
only
Clock
divider
sync
enable
Master sync
enable
0x00
0x101 fS/8 Output
Mix Control
(Global)
Open Open fS/8 start state Open Open fS/8 next
sync only
fS/8 sync
enable
0x00
0x102 FIR Filter and
Output Mode
Control
(Global)
Open Open Open Open FIR gain
0 = gain of
2
1 = gain of
1
fS/8
output
mix
disable
Complex
output
enable
FIR filter
enable
0x00
0x103 Digital Filter
Control
(Global)
Open Open Open Open Half-band
decimation
phase
Spectral
reversal
High-pass/
low-pass
select
Open 0x01
0x104 Fast Detect
Control
(Local)
Open Open Open Open Fast Detect Mode Select[2:0] Fast detect
enable
0x00
0x105 Coarse Upper
Threshold
(Local)
Open Open Open Open Open Coarse Upper Threshold[2:0] 0x00
Data Sheet AD6655
Rev. B | Page 53 of 84
Addr.
(Hex)
Register
Name
Bit 7
(MSB) Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1
Bit 0
(LSB)
Default
Value
(Hex)
Default
Notes/
Comments
0x106 Fine Upper
Threshold
Register 0
(Local)
Fine Upper Threshold[7:0] 0x00
0x107 Fine Upper
Threshold
Register 1
(Local)
Open Open Open Fine Upper Threshold[12:8] 0x00
0x108 Fine Lower
Threshold
Register 0
(Local)
Fine Lower Threshold[7:0] 0x00
0x109
Fine Lower
Threshold
Register 1
(Local)
Open
Open
Open
Fine Lower Threshold[12:8]
0x00
0x10A Increase Gain
Dwell Time
Register 0
(Local)
Increase Gain Dwell Time[7:0] 0x00 In ADC clock
cycles
0x10B Increase Gain
Dwell Time
Register 1
(Local)
Increase Gain Dwell Time[15:8] 0x00 In ADC clock
cycles
0x10C Signal
Monitor
DC
Correction
Control
(Global)
Open DC
correction
freeze
DC Correction Bandwidth(k:[3:0]) DC
correction
for signal
path
enable
DC
correction
for signal
monitor
enable
0x00
0x10D Signal
Monitor
DC Value
Channel A
Register 0
(Global)
DC Value Channel A[7:0] Read only
0x10E Signal
Monitor
DC Value
Channel A
Register 1
(Global)
Open Open DC Value Channel A[13:8] Read only
0x10F Signal
Monitor
DC Value
Channel B
Register 0
(Global)
DC Value Channel B[7:0] Read only
0x110 Signal
Monitor
DC Value
Channel B
Register 1
(Global)
Open Open DC Value Channel B[13:8] Read only
0x111 Signal
Monitor
SPORT
Control
(Global)
Open RMS
magnitude
output
enable
Peak
detector
output
enable
Threshold
crossing
output
enable
SPORT SMI SCLK
divide
00 = Undefined
01 = divide by 2
10 = divide by 4
11 = divide by 8
SPORT
SMI SCLK
sleep
Signal
monitor
SPORT
output
enable
0x04
0x112 Signal
Monitor
Control
(Global)
Complex
power
calculation
mode
enable
Open Open Open Signal
monitor
rms/ms
select
0 = rms
1 = ms
Signal monitor mode
00 = rms/ms
magnitude
01 = peak detector
10 = threshold crossing
11 = threshold crossing
Signal
monitor
enable
0x00
AD6655 Data Sheet
Rev. B | Page 54 of 84
Addr.
(Hex)
Register
Name
Bit 7
(MSB) Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1
Bit 0
(LSB)
Default
Value
(Hex)
Default
Notes/
Comments
0x113 Signal
Monitor
Period
Register 0
(Global)
Signal Monitor Period[7:0] 0x80 In ADC clock
cycles
0x114 Signal
Monitor
Period
Register 1
(Global)
Signal Monitor Period[15:8] 0x00 I In ADC clock
cycles
0x115 Signal
Monitor
Period
Register 2
(Global)
Signal Monitor Period[23:16] 0x00 In ADC clock
cycles
0x116 Signal
Monitor
Result
Channel A
Register 0
(Global)
Signal Monitor Result Channel A[7:0] Read only
0x117 Signal
Monitor
Result
Channel A
Register 1
(Global)
Signal Monitor Result Channel A[15:8] Read only
0x118 Signal
Monitor
Result
Channel A
Register 2
(Global)
Open Open Open Open Signal Monitor Result Channel A[19:16] Read only
0x119 Signal
Monitor
Result
Channel B
Register 0
(Global)
Signal Monitor Result Channel B[7:0] Read only
0x11A Signal
Monitor
Result
Channel B
Register 1
(Global)
Signal Monitor Result Channel B[15:8] Read only
0x11B Signal
Monitor
Result
Channel B
Register 2
(Global)
Open Open Open Open Signal Monitor Result Channel B[19:16] Read only
0x11D NCO Control
(Global)
Open Open Open Open Open NCO32
phase
dither
enable
NCO32
amplitude
dither
enable
NCO32
enable
0x00
0x11E NCO
Frequency 0
NCO Frequency Value[7:0] 0x00
0x11F NCO
Frequency 1
NCO Frequency Value[15:8] 0x00
0x120 NCO
Frequency 2
NCO Frequency Value[23:16] 0x00
0x121 NCO
Frequency 3
NCO Frequency Value[31:24] 0x00
0x122 NCO Phase
Offset 0
NCO Phase Value[7:0] 0x00
0x123 NCO Phase
Offset 1
NCO Phase Value[15:8] 0x00
Data Sheet AD6655
Rev. B | Page 55 of 84
MEMORY MAP REGISTER DESCRIPTION
For more information on functions controlled in Register 0x00
to Register 0xFF, see Application Note AN-877, Interfacing to
High Speed ADCs via SPI, at www.analog.com. Note that not all
test modes are supported on the AD6655.
SYNC Control (Register 0x100)
Bit 7—Signal Monitor Sync Enable
Bit 7 enables the sync pulse from the external sync input to the
signal monitor block. The sync signal is passed when Bit 7 and
Bit 0 are high. This is continuous sync mode.
Bit 6—Half-Band Next Sync Only
If the master sync enable bit (Register 0x100, Bit 0) and the half-
band sync enable bit (Register 0x100, Bit 5) are high, Bit 6 allows
the NCO32 to synchronize following the first sync pulse it
receives and ignore the rest. If Bit 6 is set, Bit 5 of Register
0x100 resets after this sync occurs.
Bit 5—Half-Band Sync Enable
Bit 5 gates the sync pulse to the half-band filter. When Bit 5
is set high, the sync signal causes the half-band to resynchro-
nize, starting at the half-band decimation phase selected in
Register 0x103, Bit 3. This sync is active only when the master
sync enable bit (Register 0x100, Bit 0) is high. This is continuous
sync mode.
Bit 4—NCO32 Next Sync Only
If the master sync enable bit (Register 0x100, Bit 0) and the
NCO32 sync enable bit (Register 0x100, Bit 3) are high, Bit 4
allows the NCO32 to synchronize following the first sync pulse it
receives and ignore the rest. Bit 3 of Register 0x100 resets after
a sync occurs if Bit 4 is set.
Bit 3—NCO32 Sync Enable
Bit 3 gates the sync pulse to the 32-bit NCO. When this bit is set
high, the sync signal causes the NCO to resynchronize, starting
at the NCO phase offset value. This sync is active only when the
master sync enable bit (Register 0x100, Bit 0) is high. This is
continuous sync mode.
Bit 2—Clock Divider Next Sync Only
If the master sync enable bit (Register 0x100, Bit 0) and the
clock divider sync enable bit (Register 0x100, Bit 1) are high,
Bit 2 allows the clock divider to synchronize following the first
sync pulse it receives and ignores the rest. Bit 1 of Register 0x100
resets after it synchronizes.
Bit 1—Clock Divider Sync Enable
Bit 1 gates the sync pulse to the clock divider. The sync signal
is passed when Bit 1 and Bit 0 are high. This is continuous
sync mode.
Bit 0—Master Sync Enable
Bit 0 must be high to enable any of the sync functions.
fS/8 Output Mix Control (Register 0x101)
Bits[7:6]—Reserved
Bits[5:4]—fS/8 Start State
Bit 5 and Bit 4 set the starting phase of the fS/8 output mix.
Bits[3:2]—Reserved
Bit 1—fS/8 Next Sync Only
If the master sync enable bit (Register 0x100, Bit 0) and the fS/8
sync enable bit (Register 0x101, Bit 0) are high, Bit 1 allows the
fS/8 output mix to synchronize following the first sync pulse it
receives and ignore the rest. Bit 0 of Register 0x100 resets after it
synchronizes.
Bit 0—fS/8 Sync Enable
Bit 0 gates the sync pulse to the fS/8 output mix. This sync is
active only when the master sync enable bit (Register 0x100,
Bit 0) is high. This is continuous sync mode.
FIR Filter and Output Mode Control (Register 0x102)
Bits[7:4]—Reserved
Bit 3—FIR Gain
When Bit 3 is set high, the FIR filter path, if enabled, has a gain
of 1. When Bit 3 set low, the FIR filter path has a gain of 2.
Bit 2—fS/8 Output Mix Disable
Bit 2 disables the fS/8 output mix when enabled. Bit 2 should be
set along with Bit 1 to enable complex output mode.
Bit 1—Complex Output Mode Enable
Setting Bit 1 high enables complex output mode.
Bit 0—FIR Filter Enable
When set high, Bit 0 enables the FIR filter. When Bit 0 is
cleared, the FIR filter is bypassed and shut down for power
savings.
AD6655 Data Sheet
Rev. B | Page 56 of 84
Digital Filter Control (Register 0x103)
Bits[7:4]—Reserved
Bit 3—Half-Band Decimation Phase
When set high, Bit 3 uses the alternate phase of the decimating
half-band filter.
Bit 2—Spectral Reversal
Bit 2 enables the spectral reversal feature of the half-band filter.
Bit 1—High-Pass/Low-Pass Select
Bit 1 enables the high-pass mode of the half-band filter when
set high. Setting this bit low enables the low-pass mode (default).
Bit 0—Reserved
Bit 0 reads back as a 1.
Fast Detect Control (Register 0x104)
Bits[7:4]—Reserved
Bits[3:1]—Fast Detect Mode Select
Bits[3:1] set the mode of the fast detect output bits according to
Table 29.
Bit 0—Fast Detect Enable
Bit 0 is used to enable the fast detect output pins. When the FD
outputs are disabled, the outputs go into a high impedance state.
In LVDS mode when the outputs are interleaved, the outputs go
high-Z only if both channels are turned off (power-down/
standby/output disabled). If only one channel is turned off
(power-down/standby/output disabled), the fast detect outputs
repeat the data of the active channel.
Coarse Upper Threshold (Register 0x105)
Bits[7:3]—Reserved
Bits[2:0]—Coarse Upper Threshold
These bits set the level required to assert the coarse upper
threshold indication (see Tabl e 25).
Fine Upper Threshold (Register 0x106 and Register 0x107)
Register 0x107, Bits[7:5]—Reserved
Register 0x107, Bits[4:0]—Fine Upper Threshold Bits[12:8]
Register 0x106, Bits[7:0]—Fine Upper Threshold Bits[7:0]
These registers provide a fine upper limit threshold. The 13-bit
value is compared to the 13-bit magnitude from the ADC block.
If the ADC magnitude exceeds this threshold value, the F_UT
indicator is set.
Fine Lower Threshold (Register 0x108 and Register 0x109)
Register 0x109, Bits[7:5]—Reserved
Register 0x109, Bits[4:0]—Fine Lower Threshold Bits[12:8]
Register 0x108, Bits[7:0]—Fine Lower Threshold Bits[7:0]
These registers provide a fine lower limit threshold. This 13-bit
value is compared with the 13-bit magnitude from the ADC
block. If the ADC magnitude is less than this threshold value,
the F_LT indicator is set.
Increase Gain Dwell Time (Register 0x10A and
Register 0x10B)
Register 0x10B, Bits[7:0]—Increase Gain Dwell Time
Bits[15:8]
Register 0x10A, Bits[7:0]—Increase Gain Dwell Time
Bits[7:0]
These register values set the minimum time in ADC sample
clock cycles (after clock divider) that a signal needs to stay below
the fine lower threshold limit before the F_LT and IG are
asserted high.
Signal Monitor DC Correction Control (Register 0x10C)
Bit 7—Reserved
Bit 6—DC Correction Freeze
When Bit 6 is set high, the dc correction is no longer updated to
the signal monitor block, which holds the last dc value
calculated.
Bits[5:2]—DC Correction Bandwidth
Bits[5:2] set the averaging time of the signal monitor dc
correction function. This 4-bit word sets the bandwidth of the
correction block, according to the following equation:
π×
×= //
2
2__ 14kCLK
f
BWCorrDC
where:
k is the 4-bit value programmed in Bits[5:2] of Register 0x10C
(values between 0 and 13 are valid for k; programming 14 or 15
provides the same result as programming 13).
fCLK is the AD6655 ADC sample rate in hertz (Hz).
Bit 1—DC Correction for Signal Path Enable
Setting this bit high causes the output of the dc measurement
block to be summed with the data in the signal path to remove
the dc offset from the signal path.
Bit 0—DC Correction for Signal Monitor Enable
This bit enables the dc correction function in the signal monitor
block. The dc correction is an averaging function that can be
used by the signal monitor to remove dc offset in the signal.
Removing this dc from the measurement allows a more
accurate power reading.
Signal Monitor DC Value Channel A (Register 0x10D and
Register 0x10E)
Register 0x10E, Bits[7:6]—Reserved
Register 0x10E, Bits[5:0]—DC Value Channel A[13:8]
Register 0x10D, Bits[7:0]—DC Va lue Channel A[7:0]
These read-only registers hold the latest dc offset value computed
by the signal monitor for Channel A.
Data Sheet AD6655
Rev. B | Page 57 of 84
Signal Monitor DC Value Channel B (Register 0x10F and
Register 0x110)
Register 0x110, Bits[7:6]—Reserved
Register 0x110, Bits[5:0]—Channel B DC Value Bits[13:8]
Register 0x10F, Bits[7:0]—Channel B DC Value Bits [7:0]
These read-only registers hold the latest dc offset value computed
by the signal monitor for Channel B.
Signal Monitor SPORT Control (Register 0x111)
Bit 7—Reserved
Bit 6—RMS/MS Magnitude Output Enable
Bit 6 enables the 20-bit rms or ms magnitude measurement as
output on the SPORT.
Bit 5—Peak Detector Output Enable
Bit 5 enables the 13-bit peak measurement as output on the SPORT.
Bit 4—Threshold Crossing Output Enable
Bit 4 enables the 13-bit threshold measurement as output on the
SPORT.
Bits[3:2]—SPORT SMI SCLK Divide
The values of these bits set the SPORT SMI SCLK divide ratio from
the input clock. A value of 0x01 sets divide by 2 (default), a value
of 0x10 sets divide by 4, and a value of 0x11 sets divide by 8.
Bit 1—SPORT SMI SCLK Sleep
Setting Bit 1 high causes the SMI SCLK to remain low when the
signal monitor block has no data to transfer.
Bit 0—Signal Monitor SPORT Output Enable
When set, Bit 0 enables the signal monitor SPORT output to
begin shifting out the result data from the signal monitor block.
Signal Monitor Control (Register 0x112)
Bit 7—Complex Power Calculation Mode Enable
This mode assumes I data is present on one channel and Q data
is present on the alternate channel. The result reported is the
complex power measured as
22 QI +
Bits[6:4]—Reserved
Bit 3—Signal Monitor RMS/MS Select
Setting Bit 3 low selects rms power measurement mode. Setting
Bit 3 high selects ms power measurement mode.
Bits[2:1]—Signal Monitor Mode
Bit 2 and Bit 1 set the mode of the signal monitor for data
output to registers at Address 0x116 through Address 0x11B.
Setting these bits to 0x00 selects rms/ms magnitude output,
setting these bits to 0x01 selects peak detector output, and
setting 0x10 or 0x11 selects threshold crossing output.
Bit 0—Signal Monitor Enable
Setting Bit 0 high enables the signal monitor block.
Signal Monitor Period (Register 0x113 to Register 0x115)
Register 0x115 Bits[7:0]—Signal Monitor Period[23:16]
Register 0x114 Bits[7:0]—Signal Monitor Period[15:8]
Register 0x113 Bits[7:0]—Signal Monitor Period[7:0]
This 24-bit value sets the number of clock cycles over which the
signal monitor performs its operation. The minimum value for
this register is 128 cycles (programmed values less than 128
revert to 128).
Signal Monitor Result Channel A (Register 0x116 to
Register 0x118)
Register 0x118, Bits[7:4]—Reserved
Register 0x118, Bits[3:0]—Signal Monitor Result
Channel A[19:16]
Register 0x117, Bits[7:0]—Signal Monitor Result
Channel A[15:8]
Register 0x116, Bits[7:0]—Signal Monitor Result
Channel A[7:0]
This 20-bit value contains the power value calculated by the
signal monitor block for Channel A. The content is dependent
on the settings in Register 0x112, Bits[2:1].
Signal Monitor Result Channel B (Register 0x119 to
Register 0x11B)
Register 0x11B, Bits[7:4]—Reserved
Register 0x11B, Bits[3:0]—Signal Monitor Result
Channel B[19:16]
Register 0x11A, Bits[7:0]—Signal Monitor Result
Channel B[15:8]
Register 0x119, Bits[7:0]—Signal Monitor Result
Channel B[7:0]
This 20-bit value contains the power value calculated by the
signal monitor block for Channel B. The content is dependent
on the settings in Register 0x112, Bits[2:1].
NCO Control (Register 0x11D)
Bits[7:3]—Reserved
Bit 2—NCO32 Phase Dither Enable
When Bit 2 is set, phase dither in the NCO is enabled. When
Bit 2 is cleared, phase dither is disabled.
Bit 1—NCO32 Amplitude Dither Enable
When Bit 1 is set, amplitude dither in the NCO is enabled.
When Bit 1 is cleared, amplitude dither is disabled.
AD6655 Data Sheet
Rev. B | Page 58 of 84
Bit 0—NCO32 Enable
When Bit 0 is set, this bit enables the 32-bit NCO operating at
the frequency programmed into the NCO frequency register.
When Bit 0 is cleared, the NCO is bypassed and shuts down for
power savings.
NCO Frequency (Register 0x11E to Register 0x121)
Register 0x11E, Bits[7:0]—NCO Frequency Value[7:0]
Register 0x11F, Bits[7:0]—NCO Frequency Value[15:8]
Register 0x120, Bits[7:0]—NCO Frequency Value[23:16]
Register 0x121, Bits[7:0]—NCO Frequency Value[31:24]
This 32-bit value is used to program the NCO tuning frequency.
The frequency value to be programmed is given by the
following equation:
CLK
CLK
f
ffMod
NCO_FREQ ),(
2
32
×=
where:
NCO_FREQ is a 32-bit twos complement number representing
the NCO frequency register.
f is the desired carrier frequency in hertz (Hz).
fCLK is the AD6655 ADC clock rate in hertz (Hz).
NCO Phase Offset (Register 0x122 and Register 0x123)
Register 0x122, Bits[7:0]—NCO Phase Value[7:0]
Register 0x123, Bits[7:0]—NCO Phase Va lue[15:8]
The 16-bit value programmed into the NCO phase value register
is loaded into the NCO block each time the NCO is started or
when an NCO SYNC signal is received. This process allows the
NCO to be started with a known nonzero phase.
Use the following equation to calculate the NCO phase offset
value:
NCO_PHASE = 216 × PHASE/360
where:
NCO_PHASE is a decimal number equal to the 16-bit binary
number to be programmed at Register 0x122 and Register 0x123.
PHASE is the desired NCO phase in degrees.
Data Sheet AD6655
Rev. B | Page 59 of 84
APPLICATIONS INFORMATION
DESIGN GUIDELINES
Before starting system-level design and layout of the AD6655,
it is recommended that the designer become familiar with these
guidelines, which discuss the special circuit connections and
layout requirements needed for certain pins.
Power and Ground Recommendations
When connecting power to the AD6655, it is recommended
that two separate 1.8 V supplies be used: one supply should be
used for analog (AVDD) and digital (DVDD), and a separate
supply should be used for the digital outputs (DRVDD). The
AVDD and DVDD supplies, while derived from the same source,
should be isolated with a ferrite bead or filter choke and separate
decoupling capacitors. The designer can employ several different
decoupling capacitors to cover both high and low frequencies.
These capacitors should be located close to the point of entry
at the PC board level and close to the pins of the part with
minimal trace length.
A single PCB ground plane should be sufficient when using the
AD6655. With proper decoupling and smart partitioning of the
PCB analog, digital, and clock sections, optimum performance
is easily achieved.
fS/2 Spurious
Because the AD6655 output data rate is at one-half the sampling
frequency, there is significant fS/2 energy in the outputs of the
part. If this fS/2 spur falls in band, care must be taken to ensure
that this fS/2 energy does not couple into either the clock circuit
or the analog inputs of the AD6655. When fS/2 energy is coupled
in this fashion, it appears as a spurious tone reflected around fS/4,
3fS/4, 5fS/4, and so on. For example, in a 125 MSPS sampling
application with a 90 MHz single-tone analog input, this energy
generates a tone at 97.5 MHz. In this example, the center of the
Nyquist zone is 93.75 MHz; therefore, the 90 MHz input signal is
3.75 MHz from the center of the Nyquist zone. As a result, the fS/2
spurious tone appears at 97.5 MHz, or 3.75 MHz above the center
of the Nyquist zone. These frequencies are then tuned by the NCOs
before being output by the AD6655.
Depending on the relationship of the IF frequency to the center
of the Nyquist zone, this spurious tone may or may not exist in the
AD6655 output band. Some residual fS/2 energy is present in
the AD6655, and the level of this spur is typically below the
level of the harmonics at clock rates of 125 MSPS and below.
Figure 82 shows a plot of the fS/2 spur level vs. analog input
frequency for the AD6655-125. At sampling rates above
125 MSPS, the fS/2 spur level increases and is at a higher level
than the worst harmonic, as shown in Figure 83, which shows
the AD6655-150 fS/2 levels.
For the specifications provided in Table 2, the fS/2 spur, if in
band, is excluded from the SNR values. It is treated as a
harmonic, in terms of SNR. The fS/2 level is included in the
SFDR and worst other specifications.
–60
–70
–80
–90
–100
–110
–120 050 100 150 200 250 350300 400 450 500
06709-083
INP UT FRE QUENC Y (MHz)
–SFDR
SFDR AND fS/2 SP UR ( dBF S )
fS/2 S P UR
Figure 82. AD6655-125 SFDR and fS/2 Spurious Level vs. Input Frequency (fIN)
with DRVDD = 1.8 V Parallel CMOS Output Mode
–60
–70
–80
–90
–100
–110
–120 050 100 150 200 250 350300 400 450 500
06709-084
ANALOG INPUT F RE QUENCY (MHz)
–SFDR
SFDR AND f
S
/2 S P UR ( dBFS )
f
S
/2 S P UR
Figure 83. AD6655-150 SFDR and fS/2 Spurious Level vs. Input Frequency (fIN)
with DRVDD = 1.8 V Parallel CMOS Output Mode
Operating the part with a 1.8 V DRVDD voltage rather than a 3.3 V
DRVDD lowers the fS/2 spur. In addition, using LVDS, CMOS
interleaved, or CMOS IQ output modes also reduces the fS/2
spurious level.
LVDS Operation
The AD6655 defaults to CMOS output mode on power-up.
If LVDS operation is desired, this mode must be programmed
using the SPI configuration registers after power-up. When the
AD6655 powers up in CMOS mode with LVDS termination
resistors (100 Ω) on the outputs, the DRVDD current can be
higher than the typical value until the part is placed in LVDS
mode. This additional DRVDD current does not cause damage
to the AD6655, but it should be taken into account when consid-
ering the maximum DRVDD current for the part.
AD6655 Data Sheet
Rev. B | Page 60 of 84
To avoid this additional DRVDD current, the AD6655 outputs
can be disabled at power-up by taking the OEB pin high. After
the part is placed into LVDS mode via the SPI port, the OEB
pin can be taken low to enable the outputs.
Exposed Paddle Thermal Heat Slug Recommendations
It is mandatory that the exposed paddle on the underside of the
ADC be connected to analog ground (AGND) to achieve the
best electrical and thermal performance. A continuous, exposed
(no solder mask) copper plane on the PCB should mate to the
AD6655 exposed paddle, Pin 0.
The copper plane should have several vias to achieve the lowest
possible resistive thermal path for heat dissipation to flow through
the bottom of the PCB. These vias should be filled or plugged with
nonconductive epoxy.
To maximize the coverage and adhesion between the ADC
and the PCB, a silkscreen should be overlaid to partition the
continuous plane on the PCB into several uniform sections.
This provides several tie points between the ADC and the PCB
during the reflow process. Using one continuous plane with no
partitions guarantees only one tie point between the ADC and
the PCB. See the evaluation board for a PCB layout example.
For detailed information about packaging and PCB layout of
chip scale packages, refer to Application Note AN-772, A Design
and Manufacturing Guide for the Lead Frame Chip Scale Package
(LFCSP) (see www.analog.com).
CML
The CML pin should be decoupled to ground with a 0.1 μF
capacitor, as shown in Figure 48.
RBIAS
The AD6655 requires that a 10 kΩ resistor be placed between
the RBIAS pin and ground. This resistor sets the master current
reference of the ADC core and should have at least a 1% tolerance.
Reference Decoupling
The VREF pin should be externally decoupled to ground with
a low ESR, 1.0 μF capacitor in parallel with a low ESR, 0.1 μF
ceramic capacitor.
SPI Port
The SPI port should not be active during periods when the full
dynamic performance of the converter is required. Because the
SCLK, CSB, and SDIO signals are typically asynchronous to the
ADC clock, noise from these signals can degrade converter
performance. If the on-board SPI bus is used for other devices,
it may be necessary to provide buffers between this bus and the
AD6655 to keep these signals from transitioning at the converter
inputs during critical sampling periods.
Data Sheet AD6655
Rev. B | Page 61 of 84
EVALUATION BOARD
The AD6655 evaluation board provides all of the support circuitry
required to operate the ADC in its various modes and configura-
tions. The converter can be driven differentially through a double
balun configuration (default) or optionally through the AD8352
differential driver. The ADC can also be driven in a single-ended
fashion. Separate power pins are provided to isolate the DUT
from the AD8352 drive circuitry. Each input configuration can
be selected by proper connection of various components (see
Figure 85 to Figure 94). Figure 84 shows the typical bench
characterization setup used to evaluate the ac performance of
the AD6655.
It is critical that the signal sources used for the analog input and
clock have very low phase noise (<<1 ps rms jitter) to realize the
optimum performance of the converter. Proper filtering of the
analog input signal to remove harmonics and lower the integrated
or broadband noise at the input is also necessary to achieve the
specified noise performance.
See Figure 85 to Figure 102 for the complete schematics and
layout diagrams that demonstrate the routing and grounding
techniques that should be applied at the system level.
POWER SUPPLIES
This evaluation board comes with a wall-mountable switching
power supply that provides a 6 V, 2 A maximum output. Connect
the supply to the rated 100 V ac to 240 V ac wall outlet at 47 Hz
to 63 Hz. The output of the supply is a 2.1 mm inner diameter
circular jack that connects to the PCB at J16. Once on the PC
board, the 6 V supply is fused and conditioned before connection
to six low dropout linear regulators that supply the proper bias
to each of the various sections on the board.
External supplies can be used to operate the evaluation board
by removing L1, L3, L4, and L13 to disconnect the voltage
regulators supplied from the switching power supply. This enables
the user to individually bias each section of the board. Use P3
and P4 to connect a different supply for each section. At least
one 1.8 V supply is needed with a 1 A current capability for
AVDD and DVDD; a separate 1.8 V to 3.3 V supply is recom-
mended for DRVDD. To operate the evaluation board using the
AD8352 option, a separate 5.0 V supply (AMP VDD) with
a 1 A current capability is needed. To operate the evaluation board
using the alternate SPI options, a separate 3.3 V analog supply
(VS) is needed, in addition to the other supplies. The 3.3 V
supply (VS) should have a 1 A current capability, as well. Solder
Jumper SJ35 allows the user to separate AVDD and DVDD,
if desired.
INPUT SIGNALS
When connecting the clock and analog source, use clean signal
generators with low phase noise, such as the Rohde & Schwarz
SMA100A signal generators or the equivalent. Use 1 m long,
shielded, RG-58, 50 Ω coaxial cable for making connections to the
evaluation board. Enter the desired frequency and amplitude for
the ADC. The AD6655 evaluation board from Analog Devices,
Inc., can accept a ~2.8 V p-p or 13 dBm sine wave input for the
clock. When connecting the analog input source, it is recom-
mended that a multipole, narrow-band, band-pass filter with 50 Ω
terminations be used. Band-pass filters of this type are available
from TTE, Allen Avionics, and K&L Microwave, Inc. Connect
the filter directly to the evaluation board, if possible.
OUTPUT SIGNALS
The parallel CMOS outputs interface directly with the Analog
Devices standard ADC data capture board (HSC-ADC-E VA LC Z ) .
For more information on the ADC data capture boards and their
optional settings, visit www.analog.com/FIFO.
06709-108
USB
CONNECTION
AD6655
EVALUATIO N BOARD
14-BIT
PARALLEL
CMOS
14-BIT
PARALLEL
CMOS
HSC-ADC-EVALCZ
FP GA BASED
DATA
CAPT URE BOARD P C RUNNING
VI S UAL ANALOG
AND SPI
CONTROLLER
SOFTWARE
1.8V – +– +
AVDD I N
VS
DRVDD I N
GND
GND
– +
5.0V
GND
AMP VDD
3.3V
6V DC
2A MAX
WALL OUTLET
100V T O 240V AC
47Hz T O 63Hz
SWITCHING
POWER
SUPPLY
– +
GND
3.3V
VCP
– +
GND
3.3V
SPI SPI
ROHDE & S CHWARZ,
SMA100A,
2V p-p SIGNAL
SYNTHESIZER CLK
ROHDE & S CHWARZ,
SMA100A,
2V p-p SIGNAL
SYNTHESIZER AINB
BAND-PASS
FILTER
ROHDE & S CHWARZ,
SMA100A,
2V p-p SIGNAL
SYNTHESIZER AINA
BAND-PASS
FILTER
Figure 84. Evaluation Board Connection
AD6655 Data Sheet
Rev. B | Page 62 of 84
DEFAULT OPERATION AND JUMPER SELECTION
SETTINGS
The following is a list of the default and optional settings or
modes allowed on the AD6655 evaluation board.
POWER
Connect the switching power supply that is provided in the
evaluation kit between a rated 100 V ac to 240 V ac wall outlet
at 47 Hz to 63 Hz and P500.
VIN
The evaluation board is set up for a double balun configuration
analog input with optimum 50 Ω impedance matching from
70 MHz to 200 MHz. For more bandwidth response, the differ-
ential capacitor across the analog inputs can be changed or
removed (see Table 14). The common mode of the analog inputs
is developed from the center tap of the transformer via the CML
pin of the ADC (see the Analog Input Considerations section).
VREF
VREF is set to 1.0 V by tying the SENSE pin to ground by adding
a jumper on Header J5 (Pin 1 to Pin 2). This causes the ADC to
operate in 2.0 V p-p full-scale range. To place the ADC in 1.0 V p-p
mode (VREF = 0.5 V), a jumper should be placed on Header J4.
A separate external reference option is also included on the evalua-
tion board. To use an external reference, connect J6 (Pin 1 to Pin 2)
and provide an external reference at TP5. Proper use of the VREF
options is detailed in the Voltage Reference section.
RBIAS
RBIAS requires a 10 kΩ resistor (R503) to ground and is used to
set the ADC core bias current.
CLOCK
The default clock input circuitry is derived from a simple balun-
coupled circuit using a high bandwidth 1:1 impedance ratio balun
(T5) that adds a very low amount of jitter to the clock path. The
clock input is 50 Ω terminated and ac-coupled to handle single-
ended sine wave inputs. The transformer converts the single-ended
input to a differential signal that is clipped before entering the
ADC clock inputs. When the AD6655 input clock divider is
utilized, clock frequencies up to 625 MHz can be input into the
evaluation board through Connector S5.
PDWN
To enable the power-down feature, connect J7, shorting the
PDWN pin to AVDD.
CSB
The CSB pin is internally pulled up, setting the chip into
external pin mode, to ignore the SDIO and SCLK information.
To connect the control of the CSB pin to the SPI circuitry on the
evaluation board, connect J21, Pin 1 to J21, Pin 2.
SCLK/DFS
If the SPI port is in external pin mode, the SCLK/DFS pin sets the
data format of the outputs. If the pin is left floating, the pin is inter-
nally pulled down, setting the default data format condition to
offset binary. Connecting J2, Pin 1 to J2, Pin 2 sets the format to
twos complement. If the SPI port is in serial pin mode, connecting
J2, Pin 2 to J2, Pin 3 connects the SCLK pin to the on-board SPI
circuitry (see the Serial Port Interface (SPI) section).
SDIO/DCS
If the SPI port is in external pin mode, the SDIO/DCS pin sets
the duty cycle stabilizer. If the pin is left floating, the pin is
internally pulled up, setting the default condition to DCS enabled.
To disable the DCS, connect J1, Pin 1 to J1, Pin 2. If the SPI port
is in serial pin mode, connecting J1, Pin 2 to J1, Pin 3 connects
the SDIO pin to the on-board SPI circuitry (see the Serial Port
Interface (SPI) section).
ALTERNATIVE CLOCK CONFIGURATIONS
Two alternate clocking options are provided on the AD6655
evaluation board. The first option is to use an on-board crystal
oscillator (Y1) to provide the clock input to the part. To enable
this crystal, Resistor R8 (0 Ω) and Resistor R85 (10 kΩ) should
be installed, and Resistor R82 and Resistor R30 should be removed.
A second clock option is to use a differential LVPECL clock to
drive the ADC input using the AD9516 (U2). When using this
drive option, the AD9516 charge pump filter components need
to be populated (see Figure 89). Consult the AD9516 data sheet
for more information.
To configure the clock input from S5 to drive the AD9516
reference input instead of directly driving the ADC, the
following components need to be added, removed, and/or
changed.
1. Remove R32, R33, R99, and R101 in the default
clock path.
2. Populate C78 and C79 with 0.001 μF capacitors and
R78 and R79 with 0 Ω resistors in the clock path.
In addition, unused AD9516 outputs (one LVDS and one LVPECL)
are routed to optional Connector S8 through Connector S11 on
the evaluation board.
Data Sheet AD6655
Rev. B | Page 63 of 84
ALTERNATIVE ANALOG INPUT DRIVE
CONFIGURATION
This section provides a brief description of the alternative
analog input drive configuration using the AD8352. When
using this particular drive option, some additional components
need to be populated. For more details on the AD8352 differential
driver, including how it works and its optional pin settings,
consult the AD8352 data sheet.
To configure the analog input to drive the AD8352 instead of
the default transformer option, the following components need
to be added, removed, and/or changed for Channel A. For
Channel B, the corresponding components should be changed.
1. Remove C1, C17, C18, and C117 in the default analog
input path.
2. Populate C8 and C9 with 0.1 µF capacitors in the analog
input path. To drive the AD8352 in the differential input
mode, populate the T10 transformer; the R1, R37, R39,
R126, and R127 resistors; and the C10, C11, and C125
capacitors.
3. Populate the optional amplifier output path with the
desired components including an optional low-pass filter.
Install 0 Ω resistors, R44 and R48. R43 and R47 should be
increased (typically to 100 Ω) to increase to 200 Ω the
output impedance seen by the AD8352.
AD6655 Data Sheet
Rev. B | Page 64 of 84
SCHEMATICS
06709-200
BA
IND0603
1 2
1
2
3
6
5
4
IND0603
12
9
12
ENB
15
6 7
4
3
2
8
13
VCM
14
VIN5
VIP
16
VON 10
VOP11
AD8352
1
VCC
GND
GND
GND
VCC
RGN
RDN
RGP
RDP
1
2
5
4
1
2
3
P S
F
5
4
1
2
3
P
S
F
1
1
5
4
1
2
3
P S
F
IND0603
1 2
1
2
IND0603
1 2
DNPDNP
DNP
OPTIONAL AMPLIFIER INPUT PATH
DEFAULTAMPLIFIER INPUT PATH
Transformer/amp channel A
AIN+
AIN-
DNPDNP
DNP
L16
180NH
R31
0OHM
C16
0.001U
R5
57.6 OHM
R1
57.6 OHM
R28
57.6 OHM
R126
4.12K
R27
33 OHM
R26
33 OHM
R41
10K OHM
R40
10K OHM
S2
AMP+A
L17
180NH
VIN-A
AVDD
R50
0OHM
VIN+A
AMP+A
AMP-A
INA+
INA-
INA-
INA+
ETC1-1-13
T10
C125
.3PF
R127
100 OHM
R121
RES0402
0OHM
R4
0OHM
R48
0OHM
R49
0OHM
R47
33 OHM
R43
33 OHM
R42
0OHM
R44
0OHM
R110
0OHM
R2
0OHM
R120
0OHM
R39
0OHM
R38
DNP
R37
0OHM
R36
DNP
R54
0OHM
R35
24.9 OHM
R29
24.9 OHM
TP15
TP14
C27
10U
C23
0.1U
C22
0.1U
ETC1-1-13
T2
ETC1-1-13
T1
CML
CML
AVDD
AMP-A
AMPVDD
C9
0.1U
C4
18PFC139
12PF
C5
4.7PF
C12
0.001U
C3
0.1U
C1
0.1U
C8
0.1U
C10
0.1U
C11
0.1U
C47
0.1U
C117
0.1U
C17
0.1U
C18
0.1U
C2
0.1U
S1
Z1
L14
120NH
ADT1_1WT
T7
L15
120NH
AMPVDD
W1
AMPVDD
Figure 85. Evaluation Board Schematic, Channel A Analog Inputs
Data Sheet AD6655
Rev. B | Page 65 of 84
06709-201
BA
ENB VCM
VIN
VIP
VON
VOP
AD8352
VCC
GND
GND
GND
VCC
RGN
RDN
RGP
RDP
PS
F
IND0603IND0603
IND0603IND0603
PS
F
PS
F
DNP DNP
DNP
DNPDNP
OPTIONAL AMPLIFIER INPUT PATH
DEFAULT AMPLIFIER INPUT PATH
AIN+
AIN-
DNP
R133
DN P
R72
57.6 OHM
R52
57.6 OHM
R51
57.6 OHM
R128
4.12K
R73
33 OHM
R74
33 OHM
R70
33 OHM
R71
33 OHM
R53
10K OHM
AMPVDD
R131
10K OHM
R135
24.9 OHM
R129
100 OHM
R69
0OHM
R67
0OHM
R123
RES0402
0OHM
R122
RES0402
0OHM
R111
0OHM
R94
0OHM
R95
0OHM
R96
0OHM
R81
0OHM
R80
0OHM
R55
0OHM
R6
0OHM
R68
DN P
R134
24.9 OHM
R132
0OHM
R66
0OHM
3
2
1
4
5
ETC1-1-1 3
T4
4
5
6
3
2
1
ADT1_1W T
T8
3
2
1
4
5
ETC1-1-1 3
T3
C51
0.1U
C28
0.1U
INB-
INB+
CML AMP-B
AMP+B
CML
VIN-B
AVDD
AVDD
AMP-B
AMP+B
AMPVDD
INB-
INB+
C19
18PF C29
12PF
C84
4.7PF
C128
.3PF
C46
0.001U
C140
0.001U
C38
0.1U
C30
0.1U
C31
0.1U
C82
0.1U
C83
0.1U
C24
0.1U
C7
0.1U
C39
0.1U
C6
0.1U
2
1
S3
2
1
S4
1
TP16
1
TP17
12
L19
120NH
12
L21
180NH
12
L20
180NH
12
L18
120NH
3
2
1
4
5
ETC1-1-1 3
T11 9
12
67
15
4
1
3
2
8
13
5
16 14
10
11
Z2
W2
C62
10U
C61
0.1U
C60
0.1U
AMPVDD
VIN+B
Figure 86. Evaluation Board Schematic, Channel B Analog Inputs
AD6655 Data Sheet
Rev. B | Page 66 of 84
06709-202
P S
F
ENC
ENC\
VS
C145
0.1U
C20
0.1U
R85
10KOHM
R8
0OHM
2 1
TP2
R84
24.9OHM
R79
0OHM
R34
DNP
R101
0OHM
R3
0OHM
R7
57.6OHM
R90
0OHM
R30
57.6OHM
R32
0OHM
R33
0OHM
R99
0OHM
R78
0OHM
R82
10KOHM
ALTCLK-
C64
0.001U
C94
0.001U
3
2
1
4
5
ETC1-1-13
T5
C79
0.001U
OPT_CLK-
CLK-
CLK+
OPT_CLK+
OPT_CLK+
C77
0.001U
C78
0.001U
C63
0.001U
C56
0.1U
C21
0.1U
2
1
SMA200UP
S6
2
1
SMA200UP
S5 4
5
6
3
2
1
ADT1_1WT
T9
OPT_CLK-
ALTCLK+
R83
24.9OHM
Figure 87. Evaluation Board Schematic, DUT Clock Input
Data Sheet AD6655
Rev. B | Page 67 of 84
06709-203
TEST
TEST
TEST
BYPASS_LD
O
CLK
CP
CP_RSE
T
GND_ES
D
GND_OUT89_DI
V
GND_REF
LD
LF
NC1
NC2
NC3
NC4
OUT0
OUT1
OUT
2
OUT3
OUT4
OUT5
OUT
6
OUT7
OUT
8
OUT
9
REFIN
REFMON
REF_SE
L
RSET_CLOC
K
SCLK
SDIO
SDO
STATU
S
VCP
VS_CLK_DIST
VS_OUT01_DI
V
VS_OUT01_DRV
VS_OUT23_DI
V
VS_OUT23_DRV
VS_OUT45_DI
V
VS_OUT45_DRV
VS_OUT67_
1
VS_OUT67_2
VS_OUT89_1
VS_OUT89_
2
VS_PLL_
1
VS_PLL_2
VS_PRESCALER
VS_REF
VS_VC
O
CLKB
CSB
OUT0B
OUT1
B
OUT2B
OUT3B
OUT4B
OUT5
B
OUT6B
OUT7B
OUT8B
OUT9B
PDB
REFINB
RESET
B
SYNCBAD9516_64LFCS
P
PAD
2
AD9516
CLK IN
LVDS
OUTPUT
LVPECL
OUTPUT
TO ADC
LVPECL
1
S7
VCXO_CLK
-
R89
49.9 OHM
R12
4.12K
R9
100 OHM
R75
100 OHM
1
TP8
2
1
S11
OUT6P
OUT6
N
10
13
5
62
44
37
59
3
9
15
18
19
20
56
53
43
40
25
28
48
46
33
35
2
7
58
22
21
6
4
12
51
54
38
41
30
27
49
5031
32
61
60
57
11
14
17
55
52
42
39
26
29
47
45
34
36
24
63
23
8
1
16
64
U2
200
R91
200
R86
R11
5.1K
200
R88
200
R92
R125
RES040
2
0OHM
R124
RES040
2
0OHM
R10
0OHM
C104
0.1U
C101
0.1UC98
0.1UC99
0.1UC96
0.1UC97
0.1U
C100
0.1U
SYNC
VCP
VS_OUT_D R
VCXO_CLK
+
1
TP18
LD1
TP19
C80
18P
F
C141
0.001
U
C86
0.1U
C85
0.1U
C87
0.1U
C88
0.1U
C143
0.1U
C142
0.1U
2
1
S10
2
1
S9
2
1
S8
1
TP20
OPT_CLK +
SCLK
VS
SYNC
B
RESETB
OPT_CLK -
PDB
CSB_2
VS
VS
VS
VS
VS
VS_OUT_DR
VS_OUT_D
R
VS
VS_OUT_D
R
VCP
SDO
SDI
REF_SE
L
LF
AGND
AGND
AGND
CP
BYPASS_LD
O
STATU
S
REFMO
N
ALTCLK
-
ALTCLK
+
Figure 88. Evaluation Board Schematic, Optional AD9516 Clock Circuit
AD6655 Data Sheet
Rev. B | Page 68 of 84
06709-204
A1
GND
A2
Y1
VCC
Y2
OUT2
OUT1
VCC
GND
OUT_DISABLE
FREQ_CTRL_V
VS-500
VALVALVAL
VAL
VAL
Charge Pump Filter
SYNC
VS
VS
C144
SEL
C92
SEL
C89
SEL
R93
R87
24.9 OH M
R98
R136R137R97R117
RES0402
0OH M
R116
RES0402
0OH M
R108
RES0402
10K OH M
R109
RES0402
10K OH M
R107
RES0402
10K OH M
R106
RES0402
10K OH M
R139
RES0402
0OH M
R114
RES0402
0OH M
R105
RES0402
10K OH M
R103
RES0402
10K OH M
R102
RES0402
10K OH M
R100
RES0402
10K OH M
SYNC
R104
RES0402
0OH M
R46
RES0402
33 OH M
200
R76
R45
RES0603
57.6 OH M
LD
RESET B
SYNC BPD BREF_SE L
VSVSVSVS
VCXO_CLK-
VCXO_CLK+
VCP
VCP
LF
CP
4
5
6
3
2
1
U25
OSCVECTRON_VS500
C91
SEL
C90
SEL
C25
0.1U
C26
0.1U
2
1
SMA200UP
S12
1TP1
4
5
6
3
2
1
NL27WZ04
U3
BYPASS_LDO
Figure 89. Evaluation Board Schematic, Optional AD9516 Loop Filter/VCO and SYNC Input
Data Sheet AD6655
Rev. B | Page 69 of 84
06709-205
J7- INSTALLFORPDWN
J8- INSTALLFOROUTPUTDISABLE
J5- INSTALLFORIVVREF/2VINPUTSPAN
J4- INSTALLFOR 0.5VVREF/IV INPUTSPAN
J6- INSTALLFOREXTERNALREFERENCEMODE
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
48
47
46
45
44
43
42
41
40
39
38
37
36
35
34
33
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
32
31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
U1
AVDD
R112
RES040 2
0OHM
R115
RES040 2
0OHM
R113
RES040 2
0OHM
1
TP6
R63
RES040 2
10KOHM
C15
1U
9
10
11
12
13
14
15
16
8
7
6
5
4
3
2
1
22ohm
RPAK8
R60
9
10
11
12
13
14
15
16
8
7
6
5
4
3
2
1
22ohm
RPAK8
R59
FD0B
9
10
11
12
13
14
15
16
8
7
6
5
4
3
2
1
22ohm
RPAK8
R57
FD1B
FD2B
FD3B
D0B
D1B
D2B
D3B
D4B
D5B
D13B
D12B
D11B
D10B
D9B
D8B
D7B
D6B
DCOB
DCOA
D0A
D1A
D2A
D3A
D4A
D5A
D6A
D7A
D8A
D9A
D10A
D11A
D12A
D13A
DVDD
AVDD
PWR_SDFS
FD0A
PWR_SDO
PWR_SCLK
FD3A
FD2A
FD1A
DRVDD
C109
0.1UC121
0.1U
C122
0.001U
C126
0.001U
C127
0.001U
C34
0.1U
C330.001U
C35
0.001U
C36
0.1U
C32
0.1U
C14
0.1U
C40
0.1UC120
0.1U5
6
7
8
4
3
2
1
22ohm
RPAK4
R58
9
10
11
12
13
14
15
16
8
7
6
5
4
3
2
1
22ohm
RPAK8
R61
1TP3
1
TP5
9
10
11
12
13
14
15
16
8
7
6
5
4
3
2
1
22ohm
RPAK8
R62
DVDD
DVDD
SYNC
SPI_CSB
CLK-
CLK+
AVDD
VIN+A
VIN-A
VIN-B
VIN+B
AVDD
AVDD
SPI_SDIO
SPI_SCLK
DRVDD
CML
DRVDD
C137
0.001U
R64
RES040 2
0OHM
AVDD1
AVDD2
CLK+
CLK-
CML
D0B_LSB_
D10A
D10B
D11A
D11B
D12A
D12B
D13A_MSB_
D13B_MSB_
D1A
D1B
D2A
D2B
D3A
D3B
D4A
D4B
D5A
D5B
D6A
D6B
D7A
D7B
D8A
D8B
D9A
D9B
DCOA
DCOB
DOA_LSB_
DRGND
DRGND1
DRVDD
DRVDD1
DVDD1DVDD2
FD0AFD0B
FD1A
FD1B
FD2A
FD2B
FD3A
FD3B
AVDD3
PWR_SCLK_PDWN
PWR_SDFS
PWR_SDO/OEB
RBIAS
SENSE
SPI_CSB
SPI_SCLK/DFS
SPI_SDIO/DCS
SYNC
VIN+A
VIN+B
VIN-A
VIN-B
VREFAD6655
Figure 90. Evaluation Board Schematic, DUT
AD6655 Data Sheet
Rev. B | Page 70 of 84
06709-206
TEST
TEST
TEST
TEST
VAL
CHANNELA
CHANNELB
DIGITAL/HSC-ADC-EVALCZ INTERFACE
48
47
46
45
44
43
42
41
40
39
38
37
36
35
34
33
32
31
30
29
28
27
26
25
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
74VCX162244MTD
U17
48
47
46
45
44
43
42
41
40
39
38
37
36
35
34
33
32
31
30
29
28
27
26
25
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
74VCX162244MTD
U16
48
47
46
45
44
43
42
41
40
39
38
37
36
35
34
33
32
31
30
29
28
27
26
25
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
74VCX162244MTD
U15
SDI
CSB
SCLK
R145
RES040 2
0OHM
R142
RES040 2
0OHM
SDO
R141
RES040 2
0OHM
R119
RES040 2
0OHM
CSB_2
V_DIG
VS
R140
RES040 2
10KOHM
R118
RES040 2
10KOHM
R130R77
100OHM
SYNC
OUT6N
OUT6P
OUT6P
OUT6N
FD0B
FD1BDG10
DG9
DG8
DG7
DG6
DG5
DG4
DG3
DG2
DG1
A1
A2
A3
A4
A5
A6
A7
A8
A9
A10
B1
B2
B3
B4
B5
B6
B7
B8
B9
B10
C1
C2
C3
C4
C5
C6
C7
C8
C9
C10
D1
D2
D3
D4
D5
D6
D7
D8
D9
D10
BG10
BG9
BG8
BG7
BG6
BG5
BG4
BG3
BG2
BG1
TYCO_HM-ZD
J11
V_DIG
V_DIG
FD2B
FD3B
D0B
D1B
D2B
D3B
V_DIG
D4B
D5B
D6B
D7B
V_DIG
V_DIG
V_DIG
V_DIG
D8B
D9B
D10B
D11B
D12B
D13B
DCOB
DCOA
D0A
D1A
D2A
D3A
D4A
D5A
D6A
D7A
D8A
D9A
D10A
D11A
V_DIG
D12A
D13A
FD3A
FD2A
FD1A
FD0A
V_DIG
PWR_SDO
PWR_SDFSSCLK_OUT
SDFS_OUT
SDO_OUT
PWR_SCLK
SDO_OUT
1
TP23
SCLK_OUTSDFS_OUT
1
TP21
V_DIG
C65
0.1U
VS
C71
0.1U
C70
0.1U
C69
0.1U
C68
0.1U
C66
0.1UC67
0.1U
C72
0.1UC73
0.1UC76
0.1U
C74
0.1UC75
0.1U
RESETB
DG10
DG9
DG8
DG7
DG6
DG5
DG4
DG3
DG2
DG1
A1
A2
A3
A4
A5
A6
A7
A8
A9
A10
B1
B2
B3
B4
B5
B6
B7
B8
B9
B10
C1
C2
C3
C4
C5
C6
C7
C8
C9
C10
D1
D2
D3
D4
D5
D6
D7
D8
D9
D10
BG10
BG9
BG8
BG7
BG6
BG5
BG4
BG3
BG2
BG1
TYCO_HM-ZD
J12
DG10
DG9
DG8
DG7
DG6
DG5
DG4
DG3
DG2
DG1
A1
A2
A3
A4
A5
A6
A7
A8
A9
A10
B1
B2
B3
B4
B5
B6
B7
B8
B9
B10
C1
C2
C3
C4
C5
C6
C7
C8
C9
C10
D1
D2
D3
D4
D5
D6
D7
D8
D9
D10
BG10
BG9
BG8
BG7
BG6
BG5
BG4
BG3
BG2
BG1
TYCO_HM-ZD
J10
1
TP22
1
TP24
V_DIG
R143
RES040 2
0OHM
R144
RES040 2
0OHM
Figure 91. Evaluation Board Schematic, Digital Output Interface
Data Sheet AD6655
Rev. B | Page 71 of 84
06709-207
Y1
VCC
Y2
A1
GND
A2
Y1
VCC
Y2
A1
GND
A2
J1- JUMPERPINS2TO 3FOR SPIOPERATION
JUMPERPINS1TO2FORDCSENABLE
J2- JUMPERPINS2TO 3FOR SPIOPERATION
JUMPERPINS1 TO 2FORTWOSCOMPLIMENT OUTPUT
J21-INSTALLJUMPERFORSPIOPERATION
1
3J2
1
3
J1
CSB_2
R23
RES060 3
100KOHM
R22
RES060 3
100KOHM
R17
RES060 3
100KOHM
R65
RES040 2
10KOHM
C81
0.1U
R24
RES040 2
10KOHM
R21
RES060 3
1KOHM
R19
RES060 3
1KOHM
R18
RES040 2
10KOHM
R20
RES060 3
1KOHM
C13
0.1U
SDI
SDO
SCLK
CSB
V_DIG
SDI
VS
SDO
V_DIG
V_DIG
V_DIG
SPI_SDIO
SPI_SCLK
SPI_CSBV_DIG
V_DIG
V_DIG
SCLK
CSB3
2
1
4
5
6
NC7WZ16P6 X
U8
3
2
1
4
5
6
NC7WZ07P6 X
U7
Figure 92. Evaluation Board Schematic, SPI Circuitry
AD6655 Data Sheet
Rev. B | Page 72 of 84
06709-208
1
P12
P23
P34
P45
P56
P6
P1
P2
P3
P4
SMDC110F
GND
IN PAD
4
OUT
ADP3334
3
FB
GND
5
8IN
IN2
71
OUT
OUT22
SD
6
BIAS
PSG
CB
CG
CG
CG
6V, 2A MAX
POWER INPU T
BNX-01 6
OPTIONAL POWER SUPPLY INPUT S
DRVDD SETTIN G
DRVD DR13R14
3.3
1.8
2.5
140K
107K
76.8K
78.7K
94.0K
147K
GND TEST POINT S
1
3
2
4
5
6
F1
VR1
21
S2A_REC T
CR12
2
1
S2A_REC T
CR11
21
SHOT_RECT
CR8
21
S2A_REC T
CR7
1
3
ADP3339
VR3
VS
DRVDDI N
C103
0.1U
SJ35
AVDDI N
C102
10U
C52
10U
VCP
F2 PWR_I N
2
1
S2A_REC T
CR10
C42
1U
2
3
1
POWER_JACK
J16
C53
10UC54
10U
C41
10U
C59
0.1U
C58
0.1U
C57
0.1U
1
TP4
2
1
10uh
IND1210
L3
1
TP25
V_DI G
DVDD
DRVD D
AVD D
DRVDDI N
AVDDI N
C45
1U
C44
1U
C43
1U
C93
0.001U
P4
12
L6
IND1210
10UH
1
TP13
1
TP12
1
TP10
1
TP9
2
1
10uh
IND1210
L11
2
1
10uh
IND1210
L10
2
1
10uh
IND1210
L4
2
1
10UH
IND1210
L9
P3
R16
RES0603
261 OH M
R13
76.8 KOH M
R14
147K OH M
Figure 93. Evaluation Board Schematic, Power Supply
Data Sheet AD6655
Rev. B | Page 73 of 84
06709-209
ADP3334
FB
GND
IN
IN2OUT
OUT2
SD
GND
IN PAD
4
OUT
GND
IN PAD
4
OUT
GND
IN PAD
4
OUT
Power Supply ByPass Capacitors
1
3
ADP333 9
VR6
1
3
ADP333 9
VR5
1
3
ADP333 9
VR4
SJ36
SJ37
C124
10UC118
10U
C119
10U
C108
0.1UC105
0.1U
C116
0.1U
C107
0.1U
C113
0.1U
VS
C114
0.1U
C115
0.1U
C111
0.1U
C112
0.1U
C110
0.1U
21 10u
h
IND1210
L12
AMPVDD
C129
1U
VCP
VCP
VS
VS_OUT_DR
3
5
8
71
2
6
VR2
C135
1U
C136
1U
C132
1U
C131
1U
C134
1U
C133
1U
C130
1U
C95
0.001U
21 10uh
IND1210
L13
21 10UH
IND1210
L1
21 10UH
IND1210
L8
PWR_IN
PWR_IN
PWR_IN
PWR_IN
R15
78.7KOHM
R25
140KOH
M
VCPVS_OUT_DRVS
Figure 94. Evaluation Board Schematic, Power Supply (Continued)
AD6655 Data Sheet
Rev. B | Page 74 of 84
EVALUATION BOARD LAYOUTS
06709-100
Figure 95. Evaluation Board Layout, Primary Side
Data Sheet AD6655
Rev. B | Page 75 of 84
06709-101
Figure 96. Evaluation Board Layout, Ground Plane
AD6655 Data Sheet
Rev. B | Page 76 of 84
06709-102
Figure 97. Evaluation Board Layout, Power Plane
Data Sheet AD6655
Rev. B | Page 77 of 84
06709-103
Figure 98. Evaluation Board Layout, Power Plane
AD6655 Data Sheet
Rev. B | Page 78 of 84
06709-104
Figure 99. Evaluation Board Layout, Ground Plane
Data Sheet AD6655
Rev. B | Page 79 of 84
0
6709-105
Figure 100. Evaluation Board Layout, Secondary Side (Mirrored Image)
AD6655 Data Sheet
Rev. B | Page 80 of 84
06709-106
Figure 101. Evaluation Board Layout, Silkscreen, Primary Side
Data Sheet AD6655
Rev. B | Page 81 of 84
0
6709-107
Figure 102. Evaluation Board Layout, Silkscreen, Secondary Side
AD6655 Data Sheet
Rev. B | Page 82 of 84
BILL OF MATERIALS
Table 30. Evaluation Board Bill of Materials (BOM)1, 2
Item Qty
Reference
Designator Description Package Manufacturer Mfg. Part Number
1 1 AD6655CE_REVB PCB PCB Analog Devices
2 55 C1 to C3, C6, C7,
C13, C14, C17, C18,
C20 to C26, C32,
C57 to C61, C65
to C76, C81 to
C83, C96 to C101,
C103, C105, C107,
C108, C110 to
C116, C145
0.1 µF, 16 V ceramic
capacitor, SMT 0402
C0402SM Murata GRM155R71C104KA88D
3 1 C80 18 pF, COG, 50 V, 5% ceramic
capacitor, SMT 0402
C0402SM Murata GJM1555C1H180JB01J
4 2 C5, C84 4.7 pF, COG, 50 V, 5% ceramic
capacitor, SMT 0402
C0402SM Murata GJM1555C1H4R7CB01J
5 10 C33, C35, C63,
C93 to C95, C122,
C126, C127, C137
0.001 µF, X7R, 25 V, 10%
ceramic capacitor, SMT 0402
C0402SM Murata GRM155R71H102KA01D
6 13 C15, C42 to C45,
C129 to C136
1 µF, X5R, 25 V, 10% ceramic
capacitor, SMT 0805
C0805 Murata GR4M219R61A105KC01D
7 10 C27, C41, C52 to
C54, C62, C102,
C118, C119, C124
10 µF, X5R, 10 V, 10% ceramic
capacitor, SMT 1206
C1206 Murata GRM31CR61C106KC31L
8 1 CR5 Schottky diode HSMS2822, SOT23 SOT23 Avago Technologies HSMS-2822-BLKG
9 2 CR6, CR9 LED RED, SMT, 0603, SS-type LED0603 Panasonic LNJ208R8ARA
10 4 CR7, CR10 to CR12 50 V, 2 A diode DO_214AA Micro Commercial Components S2A-TP
11 1 CR8 30 V, 3 A diode DO_214AB Micro Commercial Components SK33-TP
12 1 F1 EMI filter FLTHMURATABNX01 Murata BNX016-01
13 1 F2 6.0 V, 3.0 A, trip current
resettable fuse
L1206 Tyco Raychem NANOSMDC150F-2
14 2 J1, J2 3-pin, male, single row,
straight header
HDR3 Samtec TWS-1003-08-G-S
15 9 J4 to J9, J18, J19,
J21
2-pin, male, straight header HDR2 Samtec TWS-102-08-G-S
16 3 J10 to J12 Interface connector TYCO_HM_ZD Tyco 6469169-1
17 1 J14 8-pin, male, double row,
straight header
CNBERG2X4H350LD Samtec TSW-104-08-T-D
18 1 J16 DC power jack connector PWR_JACK1 Cui Stack PJ-002A
19 10 L1, L3, L4, L6, L8
to L13
10 µH, 2 A bead core, 1210 1210 Panasonic EXC-CL3225U1
20 1 P3 6-terminal connector PTMICRO6 Weiland Electric, Inc. Z5.531.3625.0
21 1 P4 4-terminal connector PTMICRO4 Weiland Electric, Inc. Z5.531.3425.0
22 3 R7, R30, R45 57.6 Ω, 0603, 1/10 W,
1% resistor
R0603 NIC Components NRC06F57R6TRF
23 27 R2, R3, R4, R32,
R33, R42, R64, R67,
R69, R90, R96, R99,
R101, R104, R110
to F113, R115,
R119, R121, R123,
R141 to R145
0 Ω, 1/16 W, 5% resistor R0402SM NIC Components NRC04ZOTRF
24 1 R13 76.8 kΩ, 0603, 1/10 W, 1% resistor R0603 NIC Components NRC06F7682TRF
25 1 R25 140 kΩ, 0603, 1/10 W, 1% resistor R0603 NIC Components NRC06F1403TRF
26 1 R14 147 kΩ, 0603, 1/10 W, 1% resistor R0603 NIC Components NRC06F1473TRF
27 1 R15 78.7 kΩ, 0603, 1/10 W, 1% resistor R0603 NIC Components NRC06F7872TRF
Data Sheet AD6655
Rev. B | Page 83 of 84
Item Qty
Reference
Designator Description Package Manufacturer Mfg. Part Number
28 1 R16 261 Ω, 0603, 1/10 W, 1% resistor R0603 NIC Components NRC06F2610TRF
29 3 R17, R22, R23 100 kΩ, 0603, 1/10 W, 1% resistor R0603 NIC Components NRC06F1003TRF
30 7 R18, R24, R63, R65,
R82, R118, R140
10 kΩ, 0402, 1/16 W, 1% resistor R0402SM NIC Components NRC04F1002TRF
31 3 R19, R21 1 kΩ, 0603, 1/10 W, 1% resistor R0603 NIC Components NRC06F1001TRF
32 9 R26, R27, R43,
R46, R47, R70,
R71, R73, R74
33 Ω, 0402, 1/16 W, 5% resistor R0402SM NIC Components NRC04J330TRF
33 5 R57, R59 to R62 22 Ω, 16-pin, 8-resistor,
resistor array
R_742 CTS Corporation 742C163220JPTR
34 1 R58 22 Ω, 8-pin, 4-resistor,
resistor array
RES_ARRY CTS Corporation 742C083220JPTR
35 1 R76 200 Ω, 0402, 1/16 W, 1% resistor R0402SM NIC Components NCR04F2000TRF
36 4 S2, S3, S5, S12 SMA, inline, male,
coaxial connector
SMA_EDGE Emerson Network
Power
142-0701-201
37 1 SJ35 0 Ω, 1/8 W, 1% resistor SLDR_PAD2MUYLAR NIC Components NRC10ZOTRF
38 5 T1 to T5 Balun TRAN6B M/A-COM MABA-007159-000000
39 1 U1 IC, AD6655 LFCSP64-9X9-9E Analog Devices AD6655BCPZ
40 1 U2 Clock distribution, PLL IC LFCSP64-9X9 Analog Devices AD9516-4BCPZ
41 1 U3 Dual inverter IC SC70_6 Fairchild Semiconductor NC7WZ04P6X_NL
42 1 U7 Dual buffer IC,
open-drain circuits
SC70_6 Fairchild Semiconductor NC7WZ07P6X_NL
43 1 U8 UHS dual buffer IC SC70_6 Fairchild Semiconductor NC7WZ16P6X_NL
44 3 U15 to U17 16-bit CMOS buffer IC TSOP48_8_1MM Fairchild Semiconductor 74VCX16244MTDX_NL
45 2 VR1, VR2 Adjustable regulator LFCSP8-3X3 Analog Devices ADP3334ACPZ
46 1 VR3 1.8 V high accuracy regulator SOT223-HS Analog Devices ADP3339AKCZ-1.8
47 1 VR4 5.0 V high accuracy regulator SOT223-HS Analog Devices ADP3339AKCZ-5.0
48 2 VR5, VR6 3.3 V high accuracy regulator SOT223-HS Analog Devices ADP3339AKCZ-3.3
49 1 Y1 Oscillator clock, VFAC3 OSC-CTS-CB3 Valpey Fisher VFAC3-BHL
50 2 Z1, Z2 High speed IC, op amp LFCSP16-3X3-PAD Analog Devices AD8352ACPZ
1 This bill of materials is RoHS compliant.
2 The bill of materials lists only those items that are normally installed in the default condition. Items that are not installed are not included in the BOM.
AD6655 Data Sheet
Rev. B | Page 84 of 84
OUTLINE DIMENSIONS
COM P LIANT T O JEDE C S TANDARDS M O-220-V M M D- 4
0.22 M IN
1
64
16
17
49
48
32
33
0.50
0.40
0.30
0.50
BSC
0.20 RE F
12° M AX 0.80 MAX
0.65 TYP
1.00
0.85
0.80
7.50 RE F
0.05 M AX
0.02 NOM
0.60 M AX
0.60
MAX
SEATING
PLANE
PI N 1
INDICATOR
7.55
7.50 S Q
7.45
PIN 1
INDICATOR
0.30
0.25
0.18
FOR PRO P E R CONNECTI ON O F
THE EXPOSED PAD, REFER TO
THE P IN CONFI GURAT IO N AND
FUNCTION DES CRIPTI ONS
SECTION OF THIS DATA SHEET.
TOP VIEW
EXPOSED
PAD
BOTTOM VIEW
9.10
9.00 S Q
8.90
8.85
8.75 S Q
8.65
06-15-2012-B
Figure 103. 64-Lead Lead Frame Chip Scale Package [LFCSP_VQ]
9 mm × 9 mm Body, Very Thin Quad
(CP-64-6)
Dimensions shown in millimeters
ORDERING GUIDE
Model1 Temperature Range Package Description Package Option
AD6655ABCPZ-150 −40°C to +85°C 64-Lead Lead Frame Chip Scale Package [LFCSP_VQ] CP-64-6
AD6655ABCPZ-125 −40°C to +85°C 64-Lead Lead Frame Chip Scale Package [LFCSP_VQ] CP-64-6
AD6655ABCPZ-105 −40°C to +85°C 64-Lead Lead Frame Chip Scale Package [LFCSP_VQ] CP-64-6
AD6655ABCPZ-80 −40°C to +85°C 64-Lead Lead Frame Chip Scale Package [LFCSP_VQ] CP-64-6
AD6655ABCPZRL7-150 −40°C to +85°C 64-Lead Lead Frame Chip Scale Package [LFCSP_VQ] CP-64-6
AD6655ABCPZRL7-125 −40°C to +85°C 64-Lead Lead Frame Chip Scale Package [LFCSP_VQ] CP-64-6
AD6655-125EBZ
Evaluation Board with AD6655 and Software
AD6655-150EBZ Evaluation Board with AD6655 and Software
1 Z = RoHS Compliant Part.
©2007–2014 Analog Devices, Inc. All rights reserved. Trademarks and
registered trademarks are the property of their respective owners.
D06709-0-1/14(B)