50 MHz to 1000 MHz
Quadrature Demodulator
AD8348
Rev. A
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responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other
rights of third parties that may result from its use. Specifications subject to change without notice. No
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Tel: 781.329.4700 www.analog.com
Fax: 781.461.3113 ©2006 Analog Devices, Inc. All rights reserved.
FEATURES
Integrated I/Q demodulator with IF VGA amplifier
Operating IF frequency 50 MHz to 1000 MHz
(3 dB IF BW of 500 MHz driven from RS = 200 Ω)
Demodulation bandwidth 75 MHz
Linear-in-decibel AGC range 44 dB
Third-order intercept
IIP3 +28 dBm @ minimum gain (FIF = 380 MHz)
IIP3 −8 dBm @ maximum gain (FIF = 380 MHz)
Quadrature demodulation accuracy
Phase accuracy 0.5°
Amplitude balance 0.25 dB
Noise figure 11 dB @ maximum gain (FIF = 380 MHz)
LO input −10 dBm
Single supply 2.7 V to 5.5 V
Power-down mode
Compact, 28-lead TSSOP package
APPLICATIONS
QAM/QPSK demodulator
W-CDMA/CDMA/GSM/NADC
Wireless local loop
LMDS
FUNCTIONAL BLOCK DIAGRAM
DIVIDE
BY 2
PHASE
SPLITTER LOIN
LOIP
8
IMX
O
VCMO
VREF
VCMO
13
IOF
S
6
IAIN
4
IOPP
3
IOPN
5
VCMO
16
QOFS
24
ENVG
21
QXMO
19
MXIN
18
MXIP
23
QAIN
25
QOPP
26
QOPN
1
28
11
10
GAIN
CONTROL
17
BIAS
CELL
IFIP
IFIN
VGIN
15
ENBL
14
V
REF
03678-001
AD8348
Figure 1.
GENERAL DESCRIPTION
The AD8348 is a broadband quadrature demodulator with an
integrated intermediate frequency (IF), variable gain amplifier
(VGA), and integrated baseband amplifiers. It is suitable for use in
communications receivers, performing quadrature demodulation
from IF directly to baseband frequencies. The baseband amplifiers
are designed to interface directly with dual-channel ADCs, such
as the AD9201, AD9283, and AD9218, for digitizing and post-
processing.
The IF input signal is fed into two Gilbert cell mixers through
an X-AMP® VGA. The IF VGA provides 44 dB of gain control.
A precision gain control circuit sets a linear-in-decibel gain char-
acteristic for the VGA and provides temperature compensation.
The LO quadrature phase splitter employs a divide-by-2 frequency
divider to achieve high quadrature accuracy and amplitude balance
over the entire operating frequency range.
Optionally, the IF VGA can be disabled and bypassed. In this
mode, the IF signal is applied directly to the quadrature mixer
inputs via the MXIP and MXIN pins.
Separate I- and Q-channel baseband amplifiers follow the baseband
outputs of the mixers. The voltage applied to the VCMO pin sets
the dc common-mode voltage level at the baseband outputs.
Typically, VCMO is connected to the internal VREF voltage, but
it can also be connected to an external voltage. This flexibility
allows the user to maximize the input dynamic range to the ADC.
Connecting a bypass capacitor at each offset compensation input
(IOFS and QOFS) nulls dc offsets produced in the mixer. Offset
compensation can be overridden by applying an external voltage
at the offset compensation inputs.
The mixers’ outputs are brought off-chip for optional filtering
before final amplification. Inserting a channel selection filter
before each baseband amplifier increases the baseband amplifiers’
signal handling range by reducing the amplitude of high level,
out-of-channel interferers before the baseband signal is fed into
the I/Q baseband amplifiers. The single-ended mixer output is
amplified and converted to a differential signal for driving ADCs.
AD8348
Rev. A | Page 2 of 28
TABLE OF CONTENTS
Features .............................................................................................. 1
Applications....................................................................................... 1
Functional Block Diagram .............................................................. 1
General Description ......................................................................... 1
Revision History ............................................................................... 2
Specifications..................................................................................... 3
Absolute Maximum Ratings............................................................ 6
ESD Caution.................................................................................. 6
Pin Configuration and Function Descriptions............................. 7
Equivalent Circuits ........................................................................... 9
Typical Performance Characteristics ........................................... 11
VGA and Demodulator ............................................................. 11
Demodulator Using MXIP and MXIN.................................... 14
Final Baseband Amplifiers ........................................................ 15
VGA/Demodulator and Baseband Amplifier......................... 16
Theory of Operation ...................................................................... 18
VGA.............................................................................................. 18
Downconversion Mixers ........................................................... 18
Phase Splitter............................................................................... 18
I/Q Baseband Amplifiers........................................................... 18
Enable........................................................................................... 18
Baseband Offset Cancellation................................................... 18
Applications..................................................................................... 20
Basic Connections...................................................................... 20
Power Supply............................................................................... 20
Device Enable ............................................................................. 20
VGA Enable ................................................................................ 20
Gain Control ............................................................................... 20
LO Inputs..................................................................................... 20
IF Inputs ...................................................................................... 20
MX Inputs ................................................................................... 20
Baseband Outputs ...................................................................... 21
Output DC Bias Level................................................................ 21
Interfacing to Detector for AGC Operation............................... 21
Baseband Filters.......................................................................... 22
LO Generation ............................................................................ 23
Evaluation Board ........................................................................ 23
Outline Dimensions ....................................................................... 28
Ordering Guide .......................................................................... 28
REVISION HISTORY
4/06—Rev. 0 to Rev. A
Updated Format..................................................................Universal
Changes to Specifications................................................................ 3
Changes to IF Inputs Section ........................................................ 20
Changes to Evaluation Board Section.......................................... 23
Changes to Table 6.......................................................................... 27
Changes to Ordering Guide .......................................................... 28
8/03—Revision 0: Initial Version
AD8348
Rev. A | Page 3 of 28
SPECIFICATIONS
VS = 5 V, TA = 25oC, FLO = 380 MHz, FIF = 381 MHz, PLO = −10 dBm, RS (LO) = 50 Ω, RS (IFIP and MXIP/MXIN) = 200 Ω, unless
otherwise noted.
Table 1.
Parameter Conditions Min Typ Max Unit
OPERATING CONDITIONS
LO Frequency Range External input = 2 × LO frequency 100 2000 MHz
IF Frequency Range 50 1000 MHz
Baseband Bandwidth 75 MHz
LO Input Level 50 Ω source −12 −10 0 dBm
VSUPPLY (VS) 2.7 5.5 V
Temperature Range −40 +85 °C
IF FRONT END WITH VGA IFIP to IMXO (QMXO),
ENVG = 5 V, IMXO/QMXO load = 1.5 kΩ
Input Impedance Measured differentially across MXIP/MXIN 200||1.1 Ω||pF
Gain Control Range 44 dB
Maximum Conversion Voltage Gain VGIN = 0.2 V (maximum voltage gain) 25.5 dB
Minimum Conversion Voltage Gain VGIN = 1.2 V (minimum voltage gain) −18.5 dB
3 dB Bandwidth 500 MHz
Gain Control Linearity VGIN = 0.4 V (+21 dB) to 1.1 V (−14 dB) ±0.5 dB
IF Gain Flatness FIF = 380 MHz ± 5% (VGIN = 1.2 V) 0.1 dB p-p
F
IF = 900 MHz ± 5% (VGIN = 1.2 V) 1.3 dB p-p
Input 1 dB Compression Point (P1dB) VGIN = 0.2 V (maximum gain) −22 dBm
VGIN = 1.2 V (maximum gain) +13 dBm
Second-Order Input Intercept (IIP2) IF1 = 385 MHz, IF2 = 386 MHz
+3 dBm each tone from 200 Ω source, 65 dBm
VGIN = 1.2 V (minimum gain)
−42 dBm each tone from 200 Ω source, 18 dBm
VGIN = 0.2 V (maximum gain)
Third-Order Input Intercept (IIP3) IF1 = 381 MHz, IF2 = 381.02 MHz
Each tone 10 dB below P1dB from
200 Ω source,
28 dBm
VGIN = 1.2 V (minimum gain)
Each tone 10 dB below P1dB from
200 Ω source,
−8 dBm
VGIN = 0.2 V (maximum gain)
LO Leakage Measured at IFIP, IFIN −80 dBm
Measured at IMXO/QMXO (LO = 50 MHz) −60 dBm
Demodulation Bandwidth Small signal 3 dB bandwidth 75 MHz
Quadrature Phase Error1LO = 380 MHz (LOIP/LOIN 760 MHz) −0.7 ±0.1 +0.7 Degrees
vs. temperature −0.0032 °/°C
vs. baseband frequency (dc to 30 MHz) +0.01 °/MHz
I/Q Amplitude Imbalance1 −0.3 ±0.05 +0.3 dB
vs. temperature 0 dB/°C
vs. baseband frequency (dc to 30 MHz) ±0.0125 dB
Noise Figure (Double Sideband) Maximum gain, from 200 Ω source,
FIF = 380 MHz
10.75 dB
Mixer Output Impedance 40 Ω
Capacitive Load Shunt from IMXO, QMXO to VCMO 0 10 pF
Resistive Load Shunt from IMXO, QMXO to VCMO 200 1.5 kΩ
Mixer Peak Output Current 2.5 mA
AD8348
Rev. A | Page 4 of 28
Parameter Conditions Min Typ Max Unit
IF FRONT END WITHOUT VGA From MXIP, MXIN to IMXO (QMXO),
ENVG = 0 V, IMXO/QMXO load = 1.5 kΩ
Input Impedance Measured differentially across MXIP/MXIN 200||1.5 Ω||pF
Conversion voltage Gain 10.5 dB
3 dB Output Bandwidth 75 MHz
IF Gain Flatness FIF = 380 MHZ ± 5% 0.1 dB p-p
F
IF = 900 MHZ ± 5% 0.15 dB p-p
Input 1 dB Compression Point (P1dB) −4 dBm
Third-Order Input Intercept (IIP3) IF1 = 381 MHz, IF2 = 381.02 MHz 14 dBm
Each tone 10 dB below P1dB from
200 Ω source
LO Leakage Measured at MXIP/MXIN −70 dBm
Measured at IMXO, QMXO −60 dBm
Demodulation Bandwidth Small signal 3 dB bandwidth 75 MHz
Quadrature Phase Error LO = 380 MHz (LOIP/LOIN 760 MHz,
single-ended)
−2 ±0.5 +2 Degrees
I/Q Amplitude Imbalance 0.25 dB
Noise Figure (Double Sideband) From 200 Ω source, FIF = 380 MHz 21 dB
I/Q BASEBAND AMPLIFIER From IAIN to IOPP/IOPN and QAIN to QOPP/
QOPN, RLOAD = 2 kΩ, single-ended to ground
Gain 20 dB
Bandwidth 10 pF differential load 125 MHz
Output DC Offset (Differential) LO leakage offset corrected using 500 pF
capacitor on IOFS, QOFS (VIOPP − VIOPN)
−50 ±12 +50 mV
Output Common-Mode Offset (VIOPP + VIOPN)/2 − VCMO −75 ±35 +75 mV
Group Delay Flatness 0 MHz to 50 MHz 3 ns p-p
Input-Referred Noise Voltage Frequency = 1 MHz 8 nV/√Hz
Output Swing Limit (Upper) VS −1 V
Output Swing Limit (Lower) 0.5 V
Peak Output Current 1 mA
Input Impedance 50||1 kΩ||pF
Input Bias Current 2 μA
RESPONSE FROM IF AND MX INPUTS TO
BASEBAND AMPLIFIER OUTPUT
IMXO and QMXO connected directly to
IAIN and QAIN, respectively
Gain From MXIP/MXIN 30.5 dB
From IFIP/IFIN, VGIN = 0.2 V 45.5 dB
From IFIP/IFIN, VGIN = 1.2 V 1.5 dB
CONTROL INPUT/OUTPUTS
VCMO Input Range VS = 5 V 0.5 1 4 V
V
S = 2.7 V 0.5 1 1.7 V
VREF Output Voltage 0.95 1 1.05 V
Gain Control Voltage Range VGIN 0.2 1.2 V
Gain Slope −55 −50 −45 dB/V
Gain Intercept Linear extrapolation back to theoretical
gain at VGIN = 0 V
55 61 67 dB
Gain Control Input Bias Current 1 μA
LO INPUTS
LOIP Input Return Loss LOIN ac-coupled to ground
(760 MHz applied to LOIP)
−6 dB
AD8348
Rev. A | Page 5 of 28
Parameter Conditions Min Typ Max Unit
POWER-UP CONTROL
ENBL Threshold Low Low = standby 0 VS/2 1 V
ENBL Threshold High High = enable VS − 1 VS/2 VSV
Input Bias Current 2 μA
Power-Up Time Time for final baseband amplifiers to be
within 90% of final amplitude
45 μs
Power-Down Time Time for supply current to be <10% of
enabled value
700 ns
POWER SUPPLIES VPOS1, VPOS2, VPOS3
Voltage 2.7 5.5 V
Current (Enabled) VS = 5 V, VENBL = 5 V 38 48 58 mA
Current (Standby) VS = 5 V, VENBL = 0 V 75 μA
1 These parameters are guaranteed but not tested in production. Limits are ±6 Σ from the mean.
AD8348
Rev. A | Page 6 of 28
ABSOLUTE MAXIMUM RATINGS
Table 2.
Parameter Rating
Supply Voltage on VPOS1, VPOS2, VPOS3 Pins 5.5 V
LO Input Power 10 dBm (re: 50 Ω)
IF Input Power 18 dBm (re: 200 Ω)
Internal Power Dissipation 450 mW
θJA 68°C/W
Maximum Junction Temperature 150°C
Operating Temperature Range −40°C to +85°C
Storage Temperature Range −65°C to +125°C
Lead Temperature (Soldering, 60 sec) 300°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.
ESD CAUTION
ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily accumulate on
the human body and test equipment and can discharge without detection. Although this product features
proprietary ESD protection circuitry, permanent damage may occur on devices subjected to high energy
electrostatic discharges. Therefore, proper ESD precautions are recommended to avoid performance
degradation or loss of functionality.
AD8348
Rev. A | Page 7 of 28
PIN CONFIGURATION AND FUNCTION DESCRIPTIONS
LOIP
1
LOIN
28
VPOS1
2
COM1
27
IOPN
3
QOPN
26
IOPP
4
QOPP
25
VCMO
5
ENVG
24
IAIN
6
QAIN
23
COM3
7
COM3
22
IMXO
8
QMXO
21
COM2
9
VPOS3
20
IFIN
10
MXIN
19
IFIP
11
MXIP
18
VPOS2
12
VGIN
17
IOFS
13
QOFS
16
VREF
14
ENBL
15
AD8348
TOP VIEW
(Not to Scale)
03678-002
Figure 2. 28-Lead TSSOP Pin Configuration
Table 3. Pin Function Descriptions—28-Lead TSSOP
Pin No. Mnemonic Description
Equivalent
Circuit
1, 28 LOIP, LOIN LO Inputs. For optimum performance, these inputs should be ac-coupled and driven
differentially. Differential drive from single-ended sources can be achieved via a balun.
To obtain a broadband 50 Ω input impedance, connect a 60.4 Ω shunt resistor between
LOIP and LOIN. Typical input drive level is equal to −10 dBm.
A
2, 12, 20 VPOS1, VPOS2,
VPOS3
Positive Supply for LO, IF, and Biasing and Baseband Sections, Respectively. These pins
should be decoupled with 0.1 μF and 100 pF capacitors.
3, 4, 25, 26 IOPN, IOPP,
QOPP, QOPN
I- and Q-Channel Differential Baseband Outputs. Typical output swing is equal to 2 V p-p
differential. The dc common-mode voltage level on these pins is set by the voltage on VCMO.
B
5 VCMO Baseband DC Common-Mode Voltage. The voltage applied to this pin sets the dc
common-mode levels for all the baseband outputs and inputs (IMXO, QMXO, IOPP, IOPN,
QOPP, QOPN, IAIN, and QAIN). This pin can be connected either to VREF or to a reference
voltage from another device (typically an ADC).
C
6, 23 IAIN, QAIN I- and Q-Channel Baseband Amplifier Inputs. The single-ended signals on these pins are
referenced to VCMO and must have a dc bias equal to the dc voltage on the VCMO pin. If
IMXO (QMXO) is dc-coupled to IAIN (QAIN), biasing will be provided by IMXO (QMXO). If
an ac-coupled filter is placed between IMXO and IAIN, these pins can be biased from the
source driving VCMO through a 1 kΩ resistor. The gain from IAIN/QAIN to the differential
outputs (IOPP/IOPN and QOPP/QOPN) is 20 dB.
D
7, 22 COM3 Ground for Biasing and Baseband Sections.
8, 21 IMXO, QMXO I- and Q-Channel Mixer Baseband Outputs. These are low impedance (40 Ω) outputs whose
bias levels are set by the voltage applied to the VCMO pin. These pins are typically connected
to IAIN and QAIN, respectively, either directly or through a filter. Each output can drive a
maximum current of 2.5 mA.
H
9 COM2 IF Section Ground.
10, 11 IFIN, IFIP IF Inputs. IFIN should be ac-coupled to ground. The single-ended IF input signal should
be ac-coupled into IFIP. The nominal differential input impedance of these pins is 200 Ω.
For a broadband 50 Ω input impedance, a minimum-loss L pad should be used; RSERIES = 174 Ω,
RSHUNT = 57.6 Ω. This provides a 200 Ω source impedance to the IF input. However, the AD8348
does not necessarily require a 200 Ω source impedance, and a single shunt 66.7 Ω resistor
can be placed between IFIP and IFIN.
E
13, 16 IOFS, QOFS I- and Q-Channel Offset Nulling Inputs. DC offsets on the I-channel mixer output (IMXO)
can be nulled by connecting a 0.1 μF capacitor from IOFS to ground. Driving IOFS with a
fixed voltage (typically a DAC calibrated such that the offset at IOPP/IOPN is nulled) can
extend the operating frequency range to include dc. The QOFS pin can likewise be used
to null offsets on the Q-channel mixer output (QMXO).
F
14 VREF Reference Voltage Output. This output voltage (1 V) is the main bias level for the device
and can be used to externally bias the inputs and outputs of the baseband amplifiers.
The typical maximum drive current for this output is 2 mA.
G
AD8348
Rev. A | Page 8 of 28
Pin No. Mnemonic Description
Equivalent
Circuit
15 ENBL Chip Enable Input. Active high. Threshold is equal to VS/2. D
17 VGIN Gain Control Input. The voltage on this pin controls the gain on the IF VGA. The gain
control voltage range is from 0.2 V to 1.2 V and corresponds to a conversion gain range
from +25.5 dB to −18.5 dB. This is the gain to the output of the mixers (that is, IMXO and
QMXO). There is an additional 20 dB of fixed gain in the final baseband amplifiers (IAIN to
IOPP/IOPN and QAIN to QOPP/QOPN). Note that the gain control function has a negative
sense (that is, increasing voltage decreases gain).
D
18, 19 MXIP, MXIN Auxiliary Mixer Inputs. If ENVG is low, the IFIP and IFIN inputs are disabled and MXIP and
MXIN are enabled, allowing the VGA to be bypassed. The auxiliary mixer inputs are fully
differential inputs that should be ac-coupled to the signal source.
I
24 ENVG Active High VGA Enable. When ENVG is high, IFIP and IFIN inputs are enabled and MXIP
and MXIN inputs are disabled. When ENVG is low, MXIP and MXIN inputs are enabled and
IFIP and IFIN inputs are disabled.
D
27 COM1 LO Section Ground.
AD8348
Rev. A | Page 9 of 28
EQUIVALENT CIRCUITS
LOIN
LOIP
COM1
V
POS1
03678-003
Figure 3. Circuit A
VCMO
V
POS3
IOPP, IOPN,
QOPP, QOPN
COM3
03678-004
Figure 4. Circuit B
VCMO
V
POS3
COM3
03678-005
Figure 5. Circuit C
IAIN, QAIN, VGIN,
ENBL, ENVG
V
POS3
COM3
03678-006
Figure 6. Circuit D
V
POS2
COM3
IFIP
IFIN
03678-007
Figure 7. Circuit E
IOFS,
QOFS
V
POS3
COM3
50µA
MAX
03678-008
Figure 8. Circuit F
AD8348
Rev. A | Page 10 of 28
V
POS2
VREF
COM2
03678-009
Figure 9. Circuit G
V
POS3
IMXO,
QMXO
COM3
03678-010
Figure 10. Circuit H
V
POS3
MXIP
MXIN
COM3
03678-011
Figure 11. Circuit I
AD8348
Rev. A | Page 11 of 28
TYPICAL PERFORMANCE CHARACTERISTICS
VGA AND DEMODULATOR
VGIN (V)
V
G
A
AND MIXER GAIN (dB)
LINEARITY ERROR (dB)
0.2 0.3 0.4
–20
–5
–10
–15
10
5
0
30
25
20
15
–6
–3
–4
–5
0
–1
–2
4
3
2
1
0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2
03678-012
T = –40°C, V
POS
= 5V, FREQ = 380MHz
LINERR T = +85°C, V
POS
= 5V, FREQ = 380MHz
LINERR T = +25°C, V
POS
= 5V, FREQ = 380MHz
LINERR T = –40°C, V
POS
= 5V, FREQ = 380MHz
T = +25°C, V
POS
= 5V, FREQ = 380MHz
T = +85°C, V
POS
= 5V, FREQ = 380MHz
Figure 12. Mixer Gain and Linearity Error vs. VGIN, VPOS = 5 V, FIF = 380 MHz,
FBB = 1 MHz, Temperature = −40°C, +25°C, +85°C
VGIN (V)
V
G
A
AND MIXER GAIN (dB)
LINEARITY ERROR (dB)
0.2 0.3 0.4
–25
–10
–15
–20
5
0
–5
25
20
15
10
–6
–3
–4
–5
0
–1
–2
4
3
2
1
0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2
03678-013
T = –40°C, V
POS
= 5V, FREQ = 900MHz
T = +85°C, V
POS
= 5V,
FREQ = 900MHz
LINERR T = +85°C, V
POS
= 5V, FREQ = 900MHz
LINERR T = +25°C, V
POS
= 5V, FREQ = 900MHz
LINERR T = –40°C, V
POS
= 5V,
FREQ = 900MHz
T = +25°C, V
POS
= 5V, FREQ = 900MHz
Figure 13. Mixer Gain and Linearity Error vs. VGIN, VPOS = 5 V, FIF = 900 MHz,
FBB = 1 MHz, Temperature = −40°C, +25°C, +85°C
VGIN (V)
V
G
A
AND MIXER GAIN (dB)
LINEARITY ERROR (dB)
0.2 0.3 0.4
–20
–5
–10
–15
10
5
0
30
25
20
15
–6
–3
–4
–5
0
–1
–2
4
3
2
1
0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2
03678-014
T = –40°C, V
POS
= 2.7V, FREQ = 380MHz
T = +85°C, V
POS
= 2.7V,
FREQ = 380MHz
LINERR T = +85°C, V
POS
= 2.7V, FREQ = 380MHz
LINERR T = –40°C, V
POS
= 2.7V,
FREQ = 380MHz
T = +25°C, V
POS
= 2.7V, FREQ = 380MHz
LINERR T = +25°C, V
POS
= 2.7V, FREQ = 380MHz
Figure 14. Mixer Gain and Linearity Error vs. VGIN, VPOS = 2.7 V, FIF = 380 MHz,
FBB = 1 MHz, Temperature = −40°C, +25°C, +85°C
VGIN (V)
V
G
A
AND MIXER GAIN (dB)
LINEARITY ERROR (dB)
0.2 0.3 0.4
–25
–10
–15
–20
5
0
–5
25
20
15
10
–6
–3
–4
–5
0
–1
–2
4
3
2
1
0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2
03678-015
T = –40°C, V
POS
= 2.7V, FREQ = 900MHz
T = +85°C, V
POS
= 2.7V,
FREQ = 900MHz
LINERR T = +85°C, V
POS
= 2.7V, FREQ = 900MHz
LINERR T = +25°C, V
POS
= 2.7V, FREQ = 900MHz
LINERR T = –40°C, V
POS
= 2.7V,
FREQ = 900MHz
T = +25°C, V
POS
= 2.7V, FREQ = 900MHz
Figure 15. Mixer Gain and Linearity Error vs. VGIN, VPOS = 2.7 V, FIF = 900 MHz,
FBB = 1 MHz, Temperature = −40°C, +25°C, +85°C
IF FREQUENCY (MHz)
V
G
A
AND MIXER GAIN (dB)
100
18
20
22
24
26
28
200 300 400 500 600 700 800 900 1000
03678-016
2.7V, 0.2V, –40°C
5V, 0.2V, –40°C
2.7V, 0.2V, +25°C
5V, 0.2V, +25°C
2.7V, 0.2V, +85°C
5V, 0.2V, +85°C
Figure 16. Gain vs. FIF, VGIN = 0.2 V, FBB = 1 MHz,
Temperature = −40°C, +25°C, +85°C
IF FREQUENCY (MHz)
V
G
A
AND MIXER GAIN (dB)
100
–30
–25
–20
–
15
200 300 400 500 600 700 800 900 1000
03678-017
5V, 1.2V, –40°C
2.7V, 1.2V, –40°C
2.7V, 1.2V, +25 °C
5V, 1.2V, +25
2.7V, 1.2V, +85 °C
5V, 1.2V, +85°C
°C
Figure 17. Gain vs. FIF, VGIN = 1.2 V, FBB = 1 MHz,
Temperature = −40°C, +25°C, +85°C
AD8348
Rev. A | Page 12 of 28
BASEBAND FREQUENCY (MHz)
V
G
A
AND MIXER GAIN (dB)
100
17
18
19
20
21
22
23
25
26
24
27
20 30 40 50 60 70 80 90 100
03678-018
2.7V, 0.2V, –40°C
5V, 0.2V, –40°C
2.7V, 0.2V, +25°C
5V, 0.2V, +25°C
2.7V, 0.2V, +85°C
5V, 0.2V, +85°C
Figure 18. Gain vs. FBB, VGIN = 0.2 V, FIF = 380 MHz, VPOS = 2.7 V, 5 V,
Temperature = −40°C, +25°C, +85°C
BASEBAND FREQUENCY (MHz)
V
G
A
AND MIXER GAIN (dB)
100
–26
–23
–20
–
17
20 30 40 50 60 70 80 90 100
03678-019
2.7V, 1.2V, –40°C
5V, 1.2V, –40°C
2.7V, 1.2V, +25°C
5V, 1.2V, +25°C
2.7V, 1.2V, +85°C
5V, 1.2V, +85°C
Figure 19. Gain vs. FBB, VGIN = 1.2 V, FIF = 380 MHz, VPOS = 2.7 V, 5 V,
Temperature = −40°C, +25°C, +85°C
VGIN (V)
INPUT 1dB COMPRESSION POINT (dBm) (re 200Ω)
0.30.2
–25
–10
–15
–20
5
0
–5
15
10
0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2
03678-020
–40°C, 2.7V, 380MHz
+25°C, 5V, 380MHz
+25°C, 2.7V, 380MHz
–40°C, 5V, 380MHz
+85°C, 5V, 380MHz
+85°C, 2.7V, 380MHz
Figure 20. Input 1 dB Compression Point (IP1dB) vs. VGIN, FIF = 380 MHz,
FBB = 1 MHz, VPOS = 2.7 V, 5 V, Temperature = −40°C, +25°C, +85°C
VGIN (V)
INPUT 1dB COMPRESSION POINT (dBm) (re 200Ω)
0.30.2
–20
–5
–10
–15
10
5
0
20
15
0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2
03678-021
–40°C, 5V, 900MHz
+85°C, 5V, 900MHz
+25°C, 2.7V, 900MHz
–40°C, 2.7V, 900MHz
+85°C, 2.7V, 900MHz
+25°C, 5V, 900MHz
Figure 21. Input 1 dB Compression Point (IP1dB) vs. VGIN, FIF = 900 MHz,
FBB = 1 MHz, VPOS = 2.7 V, 5 V, Temperature = −40°C, +25°C, +85°C
IF FREQUENCY (MHz)
INPUT IIP3 (dBm) (re 200Ω)
200100
24
26
25
28
27
30
29
300 400 500 600 700 800 900 1000
03678-022
5V, 1.2V, –40°C
2.7V, 1.2V, –40°C
2.7V, 1.2V, +25°C
5V, 1.2V, +25°C
2.7V, 1.2V, +85°C
5V, 1.2V, +85°C
Figure 22. IIP3 vs. FIF, VGIN = 1.2 V, FBB = 1 MHz, VPOS = 2.7 V, 5 V,
Temperature = −40°C, +25°C, +85°C, Tone Spacing = 20 kHz
IF FREQUENCY (MHz)
INPUT IIP3 (dBm) (re 200Ω)
100 200
–15
–10
–5
0
300 400 500 600 700 800 900 1000
2.7V, 0.2V, –40°C
2.7V, 0.2V, +25°C
2.7V, 0.2V, +85°C
5V, 0.2V, +25°C
5V, 0.2V, +85°C
5V, 0.2V, –40°C
03678-023
Figure 23. IIP3 vs. FIF, VGIN = 0.2 V, FBB = 1 MHz, VPOS = 2.7 V, 5 V,
Temperature = −40°C, +25°C, +85°C
AD8348
Rev. A | Page 13 of 28
BASEBAND FREQUENC Y (MHz)
V
G
A
AND MIXER INPUT IIP3 (dBm) (re 200Ω)
10020
22
26
24
28
30
32
30 40 50 60 70 80 90 100
5V, 1.2V, +25°C
5V, 1.2V, –40°C
2.7V, 1.2V, +25°C
5V, 1.2V, +85°C
2.7V, 1.2V, –40°C
2.7V, 1.2V, +85°C
03678-024
Figure 24. IIP3 vs. FBB, VGIN = 1.2 V, FIF = 380 MHz, VPOS = 2.7 V, 5 V,
Temperature = −40°C, +25°C, +85°C
BASEBAND FREQUENC Y (MHz)
V
G
A
AND MIXER INPUT IIP3 (dBm) (re 200Ω)
10020
–20
–15
–10
–5
0
30 40 50 60 70 80 90 100
5V, 0.2V, +25°C
5V, 0.2V, –40°C
2.7V, 0.2V, –40°C
03678-025
5V, 0.2V, +85°C
2.7V, 0.2V, +85°C
2.7V, 0.2V, +25°C
Figure 25. IIP3 vs. FBB, VGIN = 0.2 V, FIF = 380 MHz, VPOS = 2.7 V, 5 V,
Temperature = −40°C, +25°C, +85°C
IF FREQUENCY (MHz)
NOISE FIGURE (dB)
15050 250
8
9
10
11
12
13
14
15
16
350 450 550 650 750 850 950
03678-026
NF VGIN = 0.2V
Figure 26. Noise Figure vs. FIF, T = 25°C, VGIN = 0.2 V, FBB = 1 MHz
VGIN (V)
NOISE FIGURE (dB)
INPUT IIP3 (dBm) (re 200Ω)
0.2 0.3 0.4
0
15
10
5
30
25
20
45
40
35
–10
5
0
–5
15
10
35
30
25
20
0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2
03678-027
NF
IIP3
Figure 27. Noise Figure and IIP3 vs. VGIN, Temperature = 25°C,
FIF = 380 MHz, FBB = 1 MHz, VPOS = 2.7 V
VGIN (V)
NOISE FIGURE (dB)
INPUT IIP3 (dBm) (re 200Ω)
0.2 0.3 0.4
0
15
10
5
30
25
20
40
35
–10
5
0
–5
15
10
35
30
25
20
0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2
03678-028
NF
IIP3
Figure 28. Noise Figure and IIP3 vs. VGIN, Temperature = 25°C,
FIF = 380 MHz, FBB = 1 MHz, VPOS = 5 V
LO INPUT LEVEL (V)
NOISE FIGURE (dB)
PHASE ERROR (Degrees)
–12 –10
8
11
10
9
14
13
12
16
15
–2.0
–0.5
–1.0
–1.5
0
2.0
1.5
1.0
0.5
–8 –6 –4 –2 0
03678-029
NF @ LO = 50MHz
NF @ LO = 380MHz
NF @ LO = 900MHz
PHASE ERROR 50MHz PHASE ERROR 380MHz
PHASE ERROR 900MHz
Figure 29. Noise Figure and Quadrature Phase Error IMXO/QMXO vs. LO Input
Level, Temperature = 25°C, VGIN = 0.2 V, VPOS = 5 V for FIF = 50 MHz,
380 MHz, and 900 MHz
AD8348
Rev. A | Page 14 of 28
DEMODULATOR USING MXIP AND MXIN
IF FREQUENCY (MHz)
MIXER GAIN (dB)
100 200
8.5
8.0
10.0
9.5
9.0
11.0
10.5
300 400 500 600 700 800 900 1000
03678-030
TEMP = –40°C, V
POS
= 5V
TEMP = +25°C,
V
POS
= 5V
TEMP = +85°C,
V
POS
= 2.7V
TEMP = +85°C, V
POS
= 5V
TEMP = –40°C, V
POS
= 2.7V
TEMP
= +25°C,
V
POS
= 2.7V
Figure 30. Mixer Gain vs. FIF, VPOS = 2.7 V, 5 V, FBB = 1 MHz,
Temperature = −40°C, +25°C, +85°C
IF FREQUENCY (MHz)
MIXER INPUT P1dB (dBm) (re 200Ω)
100 200
–8.0
–6.5
–7.0
–7.5
–3.0
–2.5
–2.0
–3.5
–4.0
–4.5
–5.0
–5.5
–6.0
–
1.5
300 400 500 600 700 800 900 1000
03678-031
TEMP = –40°C, V
POS
= 2.7V
TEMP = –40°C, V
POS
= 5V
TEMP = +25°C, V
POS
= 2.7V
TEMP = +25°C, V
POS
= 5V
TEMP = +85°C, V
POS
= 2.7V
TEMP = +85°C, V
POS
= 5V
Figure 31. Input 1 dB Compression Point vs. FIF, FBB = 1 MHz, VPOS = 2.7 V, 5 V,
Temperature = −40°C, +25°C, +85°C
IF FREQUENCY (MHz)
INPUT IIP3 (dBm) (re 200Ω)
50 150
10
14 21.0
13
12
11
17
16
15
18
250 350 450 550 650 750 850 950
03670-032
IIP3 2.7V
IIP3 5V
NF 2.7V
NF 5V
NOISE FIGURE (dB)
19.0
20.5
20.0
19.5
23.0
22.5
22.0
21.5
Figure 32. IIP3 and Noise Figure vs. FIF, VPOS = 2.7 V, 5 V, Temperature = 25°C
AD8348
Rev. A | Page 15 of 28
FINAL BASEBAND AMPLIFIERS
BASEBAND FREQUENCY (MHz)
GAIN (dB)
0.1
14
13
17
16
15
20
19
18
21
1 10 100 1000
03678-033
+25°C, 5V
+85°C, 2.7V
–40°C, 5V
+25°C, 2.7V
–40°C, 2.7V
+85°C, 5V
Figure 33. Gain vs. FBB, VVCMO = VREF = 1 V, VPOS = 2.7 V, 5 V,
Temperature = −40°C, +25°C, +85°C
BASEBAND FREQUENCY (MHz)
OP1dB (dBV)
0.1
–15
–20
–10
0
–5
5
1 10 100 1000
03678-034
+25°C, 5V +85°C, 5V
+25°C, 2.7V
–40°C, 2.7V
+85°C, 2.7V
–40°C, 5V
Figure 34. OP1dB Compression vs. FBB, VVCMO = VREF = 1 V, VPOS = 2.7 V, 5 V,
Temperature = −40°C, +25°C, +85°C
BASEBAND FREQUENCY (MHz)
OIP3 (dBV)
10
–10
10
15
20
25
30
–15
–5
0
5
35
50 70 9030 130110 150 170 190
03678-035
–40°C, 2.7V
+25°C, 2.7V
–40°C, 5V
+25°C, 5V
+85°C, 5V
+85°C, 2.7V
Figure 35. OIP3 vs. FBB, VVCMO = VREF = 1 V, VPOS = 2.7 V, 5 V,
Temperature = −40°C, +25°C, +85°C
FREQUENCY (kHz)
BASEBAND AMPLIFIER INPUT NOISE
SPECTRAL DENSITY (nV/ Hz)
1
1
5
6
7
8
9
0
2
3
4
10
10 100 1000 10000 100000
03678-036
Figure 36. Noise Spectral Density
AD8348
Rev. A | Page 16 of 28
VGA/DEMODULATOR AND BASEBAND AMPLIFIER
IF FREQUENCY (MHz)
QUADR
A
TURE PHASE ERROR (Degrees)
100
–1.5
0
0.5
1.0
1.5
–2.0
–1.0
–0.5
2.0
200 300 400 500 600 700 800 900 1000
03678-037
2.7V, 0.2V, –40°C
2.7V, 0.2V, +25°C
5V, 0.2V, –40°C
2.7V, 0.2V, +85°C
5V, 0.2V, +25°C
5V, 0.2V, +85°C
Figure 37. Quadrature Phase Error vs. FIF, VGIN = 0.7 V, VPOS = 2.7 V, 5 V,
Temperature = −40°C, +25°C, +85°C
BASEBAND FREQUENC Y (MHz)
QUADR
A
TURE PHASE ERROR (Degrees)
–1.5
0
0.5
1.0
1.5
–2.0
–1.0
–0.5
2.0
50 10152025303540
03678-038
5V, 0.7V, +85°C
2.7V, 0.7V, +85°C
2.7V, 0.7V, –40°C
5V, 0.7V, –40°C
2.7V, 0.7V, +25°C
5V, 0.7V, +25°C
Figure 38. Quadrature Phase Error vs. FBB, VGIN = 0.7 V, VPOS = 2.7 V, 5 V,
Temperature = −40°C, +25°C, +85°C, FIF = 380 MHz
BASEBAND FREQUENC Y (MHz)
I/Q AMPLITUDE MISM
A
TCH (dB)
–0.4
–0.2
0
0.2
0.4
50 10152025303540
03678-039
5V, 0.7V, 25°C
Figure 39. I/Q Amplitude Imbalance vs. FBB, Temperature = 25°C, VPOS = 5 V
IF FREQUENCY (MHz)
I/Q AMPLITUDE MISM
A
TCH (dB)
–1.5
0
0.5
1.0
1.5
–2.0
–1.0
–0.5
2.0
200100 300 400 500 600 700 800 900 1000
03678-040
Figure 40. I/Q Amplitude Imbalance vs. FIF, Temperature = 25°C, VPOS = 5 V
IF FREQUENCY (MHz)
SHUNT RESISTANCE (Ω)
SHUNT CAPACITANCE (pF)
50 150 250
100
160
140
120
220
200
180
300
280
260
240
0.2
0.8
0.6
0.4
1.4
1.2
1.0
2.2
2.0
1.8
1.6
350 450 550 650 750 850 950
03678-041
SHUNT CAPACITANCE
SHUNT RESISTANCE
Figure 41. Input Impedance of IF Input vs. FIF, VGIN = 0.7 V, VPOS = 5 V
0180
30
330
60
90
270
300
120
240
150
210
IMPEDANCE CIRCLE
IFIP WITH L PAD
IFIP WITHOUT L PAD
03678-042
Figure 42. S11 of IF Input vs. FIF, FIF = 50 MHz to 1 GHz, VGIN = 0.7 V,
VPOS = 5 V (with L Pad, with No Pad, Normalized to 50 Ω)
AD8348
Rev. A | Page 17 of 28
IF FREQUENCY (MHz)
SHUNT RESISTANCE (Ω)
SHUNT CAPACITANCE (pF)
50
100
150
200
100
160
140
120
220
200
180
300
280
260
240
0
0.5
2.5
2.0
1.5
1.0
250
300
350
400
450
550
650
750
850
950
500
600
700
800
900
1000
03678-043
(SHUNT CAPACITANCE)
(SHUNT RESISTANCE)
Figure 43. Input Impedance of Mixer Input vs. FIF, VGIN = 0.7 V, VPOS = 5 V
0180
30
330
60
90
270
300
120
240
150
210
IMPEDANCE CIRCLE
MX INPUTS WITH 4:1 BALUN
MXIP INPUT PIN
03678-044
Figure 44. S11 of Mixer Input vs. FIF, FIF = 50 MHz to 1 GHz,
VGIN = 0.7 V, VPOS = 5 V (With and Without Balun)
EXTERNAL LO FREQUENCY (MHz)
RETURN LOSS (dB)
–30
–15
–10
–5
–35
–25
–20
0
400
500
200
100
300
600
700
800
900
1000
1100
1200
1300
1400
1500
1600
1700
1800
1900
2000
03678-045
RETURN LOSS LOIP PIN SINGLE-ENDED,
LOIN AC-COUPLED TO GROUND.
Figure 45. Return Loss of LOIP Input vs. External LO Frequency
FREQUENCY APPLIED TO LOIP/LOIN (MHz)
RETURN LOSS (dB)
–20
–15
–10
–5
–35
–30
–25
0
400
500
200
100
300
600
700
800
900
1000
1100
1200
1300
1400
1500
1600
1700
1800
1900
2000
03678-046
RETURN LOSS LO INPUT, THROUGH BALUN
WITH 60.4Ω IN SHUNT BETWEEN LOIP/LOIN
Figure 46. Return Loss of LO Input vs. External LO Frequency
Through Balun, with Termination Resistor
TEMPERATURE (°C)
SUPPLY CURRENT (mA)
50
55
60
35
40
45
65
–30–40 –20 –10 0 10 20 30 40 50 60 70 80
03678-047
V
S
= 5V
V
S
= 2.7V
Figure 47. Supply Current vs. Temperature
AD8348
Rev. A | Page 18 of 28
THEORY OF OPERATION
DIVIDE
BY 2
PHASE
SPLITTER LOIN
LOIP
IMX
O
VCMO
VREF
VCMO
IOF
S
IAIN IOPP IOPN
VCMO
QOFSENVG QXMOMXINMXIP QAIN QOPP QOPN
GAIN
CONTROL
BIAS
CELL
IFIP
IFIN
VGIN
ENBL
V
REF
03678-049
18 2419 21 16 23 25 26
28
1
5
34613814
15
11
10
17
AD8348
Figure 48. Functional Block Diagram
VGA
The VGA is implemented using the patented X-AMP architecture.
The single-ended IF signal is attenuated in eight discrete 6 dB
steps by a passive R-2R ladder. Each discrete attenuated version
of the IF signal is applied to the input of a transconductance
stage. The current outputs of all transconductance stages are
summed together and drive a resistive load at the output of the
VGA. Gain control is achieved by smoothly turning on and
off the relevant transconductance stages with a temperature-
compensated interpolation circuit. This scheme allows the gain
to continuously vary over a 44 dB range with linear-in-decibel
gain control. This configuration also keeps the relative dynamic
range constant (for example, IIP3 − NF in dB) over the gain
setting; however, the absolute intermodulation intercepts and
noise figure vary directly with gain. The analog voltage VGIN
sets the gain. VGIN = 0.2 V is the maximum gain setting, and
VGIN = 1.2 V is the minimum voltage gain setting.
DOWNCONVERSION MIXERS
The output of the VGA drives two (I and Q) double-balanced
Gilbert cell downconversion mixers. Alternatively, driving the
ENVG pin low can disable the VGA, and the mixers can be
externally driven directly via the MXIP and MXIN ports. At
the input of the mixer, a degenerated differential pair performs
linear voltage-to-current conversions. The differential output
current feeds into the mixer core where it is downconverted by
the mixing action of the Gilbert cell. The phase splitter provides
quadrature LO signals that drive the LO ports of the in-phase
and quadrature mixers.
Buffers at the output of each mixer drive the IMXO and QMXO
pins. These linear, low output impedance buffers drive 40 Ω,
temperature-stable, passive resistors in series with each output
pin (IMXO and QMXO). This 40 Ω should be considered when
calculating the reverse termination if an external filter is inserted
between IMXO (QMXO) and IAIN (QAIN). The VCMO pin sets
the dc output level of the buffer. This can be set externally or
connected to the on-chip 1.0 V reference, VREF.
PHASE SPLITTER
Quadrature generation is achieved using a divide-by-2 frequency
divider. Unlike a polyphase filter that achieves quadrature over
a limited frequency range, the divide-by-2 approach maintains
quadrature over a broad frequency range and does not attenuate
the LO. The user, however, must provide an external signal XLO
that is twice the frequency of the desired LO frequency. XLO drives
the clock inputs of two flip-flops that divide down the frequency
by a factor of 2. The outputs of the two flip-flops are one-half
period of XLO out of phase. Equivalently, the outputs are one-
quarter period (90°) of the desired LO frequency out of phase.
Because the transitions on XLO define the phase difference at
the outputs, deviation from 50% duty cycle translates directly to
quadrature phase errors.
If the user generates XLO from a 1× frequency (fREF) and a
frequency-doubling circuit (XLO = 2 × fREF), fundamentally
there is a 180° phase uncertainty between fREF and the AD8348
internal quadrature LO. The phase relationship between I and Q
LO, however, is always 90°.
I/Q BASEBAND AMPLIFIERS
Two (I and Q) fixed gain (20 dB), single-ended-to-differential
amplifiers are provided to amplify the demodulated signal
after off-chip filtering. The amplifiers use voltage feedback to
linearize the gain over the demodulation bandwidth. These
amplifiers can be used to maximize the dynamic range at the
input of an ADC following the AD8348.
The input to the baseband amplifiers, IAIN (QAIN), feeds into
the base of a bipolar transistor with an input impedance of
roughly 50 kΩ. The baseband amplifiers sense the single-ended
difference between IAIN (QAIN) and VCMO. IAIN (QAIN)
can be dc biased by terminating it with a shunt resistor to
VCMO, such as when an external filter is inserted between
IMXO (QMXO) and IAIN (QAIN). Alternatively, any dc
connection to IMXO (QXMO) can provide appropriate bias via
the offset-nulling loop.
ENABLE
A master biasing cell that can be disabled using the ENBL pin
controls the biasing for the chip. If the ENBL pin is held low,
the entire chip powers down to a low power sleep mode,
typically consuming 75 µA at 5 V.
BASEBAND OFFSET CANCELLATION
A low output current integrator senses the output voltage offset
at IOPP and IOPN (QOPP and QOPN) and injects a nulling
current into the signal path. The integration time constant of the
offset-nulling loop is set by Capacitor COFS from IOFS (QOFS) to
AD8348
Rev. A | Page 19 of 28
VCMO. This forms a high-pass response for the baseband
signal path with a lower 3 dB frequency of
COFS
fPASS ×Ω×π
=
26502
1
Alternatively, the user can externally adjust the dc offset by driving
IOFS (QOFS) with a digital-to-analog converter or other voltage
source. In this case, the baseband circuit operates all the way down
to dc (fPASS = 0 Hz). The integrator output current is only 50 µA
and can be easily overridden with an external voltage source.
The nominal voltage level applied to IOFS (QOFS) to produce
a 0 V differential offset at the baseband outputs is 900 mV.
The IOFS (QOFS) pin must be connected to either a bypass
capacitor (>0.1 µF) or an external voltage source to prevent the
feedback loop from oscillating.
The feedback loop will be broken at dc if an ac-coupled baseband
filter is placed between the mixer outputs and the baseband
amplifier inputs. If an ac-coupled filter is implemented, the user
must handle the offset compensation via some external means.
AD8348
Rev. A | Page 20 of 28
APPLICATIONS
BASIC CONNECTIONS
Figure 49 shows the basic connections schematic for the AD8348.
C32
1000pF
C31
1000pF
R31
57.6Ω
13
54
J21
LO
C21
1000pF
C22
1000pF
R21
60.4Ω
+V
S
C0Q
0.1µF
C11
4.7µF
IFIP
R32
174Ω
T21
ETC1-1-13
IFIP MXIP
VPOS2 VGIN
IOFS QOFS
VREF ENBL
LOINLOIP
VPOS1 COM1
IOPN QOPN
IOPP QOPP
VCMO ENVG
IAIN QAIN
COM3 COM3
IMXO QMXO
COM2 VPOS3
IFIN MXIN
AD8348
C0l
0.1µF
J2I
IOPP
J3I
IOP
N
J2Q
QOPP
J3Q
QOPN
C53
100pF
C54
0.1µF
+V
S
C51
100pF
C52
0.1µF
+V
S
V
REF
SW12
+V
S
IF
MX
SW11
+V
S
ENBL
DENBL
C55
100pF
C56
0.1µF
VGIN
MXIP
R42
0Ω
T41
ETK4-2T
C41
1µF
C43
1000pF
C42
1000pF
03678-064
18
17
16
15
28
27
26
25
24
23
22
21
20
19
11
12
13
14
1
2
3
4
5
6
7
8
9
10
Figure 49. Basic Connections Schematic
POWER SUPPLY
The voltage supply for the AD8348, between 2.7 V and 5 V, should
be provided to the +VPOSx pins, and ground should be connected
to the COMx pins. Each supply pin should be decoupled separately
using two capacitors whose recommended values are 100 pF and
0.1 F (values close to these can also be used).
DEVICE ENABLE
To enable the device, the ENBL pin should be driven to VS.
Grounding the ENBL pin disables the device.
VGA ENABLE
Driving the voltage on the ENVG pin to VS enables the VGA. In
this mode, the MX inputs are disabled and the IF inputs are
used. Grounding the ENVG pin disables the VGA and the IF
inputs. When the VGA is disabled, the MX inputs should be used.
GAIN CONTROL
When the VGA is enabled, the voltage applied to the VGIN pin sets
the gain. The gain control voltage range is between 0.2 V and 1.2 V.
This corresponds to a gain range between +25.5 dB and −18.5 dB.
LO INPUTS
For optimum performance, the local oscillator port should be
driven differentially through a balun. The recommended balun
is M/A-COM ETC1-1-13. The LO inputs to the device should
be ac-coupled, unless an ac-coupled transformer is being used.
For a broadband match to a 50 Ω source, a 60.4 Ω resistor
should be placed between the LOIP and LION pins.
128
LOIP LOIN
60.4Ω
31
45
1000pF 1000pF
ETC1-1-13
LO
03678-050
Figure 50. Differential LO Drive with Balun
Alternatively, the LO port can be driven from a single-ended source
without a balun (Figure 51). The LO signal is ac-coupled directly
into the LOIP pin via an ac-coupling capacitor, and the LOIN pin
is ac-coupled to ground. Driving the LO port from a single-
ended source results in an increase in both quadrature phase
error and LO leakage.
128
LOIP LOIN
60.4Ω
1000pF 1000pF
LO
03678-051
Figure 51. Single-Ended LO Drive
The recommended LO drive level is between −12 dBm and
0 dBm. The LO frequency at the input to the device should be
twice that of the desired LO frequency at the mixer core. The
applied LO frequency range is between 100 MHz and 2 GHz.
IF INPUTS
The IF inputs have an input impedance of 200 Ω. A broadband
50 Ω match can be presented to the driving source through the use
of a minimum-loss L pad. This minimum-loss pad introduces
an 11.46 dB loss in the input path and must be taken into account
when calculating metrics such as gain and noise figure. Figure 42
shows the S11 of the IF input with and without the L pad.
11
10
1000pF
1000pF
174Ω
57.6Ω
IFIP IFIP
IFIN
03678-052
Figure 52. Minimum-Loss L Pad for 50 Ω IF Input
MX INPUTS
The mixer inputs, MXIP and MXIN, have a nominal impedance
of 200 Ω and should be driven differentially. When driven from
a differential source, the input should be ac-coupled to the
source via capacitors, as shown in Figure 53.
AD8348
Rev. A | Page 21 of 28
18
19
1000pF
1000pF
MXIP MXIP
MXINMXIN
03678-053
Figure 53. Driving the MX Inputs from a Differential Source
If the MX inputs are to be driven from a single-ended 50 Ω source,
a 4:1 balun can be used to transform the 200 Ω impedance of
the inputs to 50 Ω while performing the required single-ended-
to-differential conversion. The recommended transformer is the
M/A-COM ETK4-2T.
03678-066
MXIP
1000pF
1000pF
ETK4-2T
1µF
MXIP
MXIN
18
19
Figure 54. Driving the MX Inputs from a Single-Ended 50 Ω Source
BASEBAND OUTPUTS
The baseband amplifier outputs, IOPP, IOPN, QOPP, and QOPN,
should be presented with loads of at least 2 kΩ (single-ended to
ground). They are not designed to drive 50 Ω loads directly. The
typical swing for these outputs is 2 V p-p differential (1 V p-p
single-ended), but larger swings are possible as long as care is taken
to ensure that the signals remain within the lower limit of 0.5 V
and the upper limit of VS − 1 V of the output swing. To achieve
a larger swing, it is necessary to adjust the common-mode bias of
the baseband output signals. Increasing the swing can have the
benefit of improving the signal-to-noise ratio of the baseband
amplifier output.
When connecting the baseband outputs to other devices, care
should be taken to ensure that the outputs are not capacitively
loaded by approximately 20 pF or more. Such loads could
potentially overload the output or induce oscillations. The effect
of capacitive loading on the baseband amplifier outputs can be
mitigated by inserting series resistors of approximately 200 Ω.
OUTPUT DC BIAS LEVEL
The dc bias of the mixer outputs and the baseband amplifier
inputs and outputs is determined by the voltage that is driven
onto the VCMO pin. The range of this voltage is typically
between 500 mV and 4 V when operating with a 5 V supply.
To achieve maximum voltage swing from the baseband amplifiers,
VCMO should be driven at 2.25 V; this allows a swing of up to
7 V p-p differential (3.5 V p-p single-ended).
INTERFACING TO DETECTOR FOR AGC OPERATION
The AD8348 can be interfaced with a detector such as the
AD8362 rms-to-dc converter to provide an automatic signal-
leveling function for the baseband outputs.
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
1000pF
1000pF
13
54
L
O
1000pF 1000pF
60.4Ω
1:1
AD8348
100pF0.1µF
+V
S
V
REF
+V
S
+V
S
100pF
100pF
V
REF
1000pF
100pF
1000pF
1µF
1µF
1µF
1µF 100pF 0.1µF
1µF
1000pF
+V
S
0.1µF100pF
+V
S
0.1µF 100pF
V
CMO
V
SET
+V
S
AD8362
ACOMCOMM
VTGTDECL
VPOSINHI
VOUTINLO
ACOMPWDN
CLPFCOMM
VREFCHPF
VSETDECL
TO BASEBAND
Q ADC
TO BASEBAND
I ADC
IF INPUT
Z
O
= 200Ω
1.02kΩ1.24kΩ
03678-0-055
IFIP MXIP
VPOS2 VGIN
IOFS QOFS
VREF ENBL
LOINLOIP
VPOS1 COM1
IOPN QOPN
IOPP QOPP
VCMO ENVG
IAIN QAIN
COM3 COM3
IMXO QMXO
COM2 VPOS3
IFIN MXIN
18
17
16
15
28
27
26
25
24
23
22
21
20
19
11
12
13
14
1
2
3
4
5
6
7
8
9
10
Figure 55. AD8362 Configuration for AGC Operation
Assuming the I and Q channels have the same rms power, the
mixer output (or the output of the baseband filter) of one channel
can be used as the input of the AD8362. The AD8362 should be
operated in a region where its linearity error is small. Also, a
voltage divider should be implemented with an external resistor
in series with the 200 Ω input impedance of the AD8362 input.
This attenuates the AD8348 mixer output so that the AD8362
input is not overdriven. The size of the resistor between the
mixer output and the AD8362 input should be chosen so that
the peak signal level at the input of the AD8362 is about 10 dB
less than the approximately 10 dBm maximum of the AD8362
dynamic range.
The other side of the AD8348 baseband output should be
loaded with a resistance equal to the series resistance of the
attenuating resistor in series with the AD8362’s 200 Ω input
impedance. This resistor should be tied to the source driving
VCMO so that there is no dc drawn from the mixer output.
AD8348
Rev. A | Page 22 of 28
The level of the mixer output (or the output of the baseband
filter) can then be set by varying the setpoint voltage fed to
Pin 11 (VSET) of the AD8362.
Care should be taken to ensure that blockers—unwanted signals
in the band of interest that are demodulated along with the desired
signal—do not dominate the rms power of the AD8362 input.
This can cause an undesired reduction in the level of the mixer
output. To overcome this, baseband filtering can be implemented
to filter out undesired signals before the signal is presented to
the AD8362.
Figure 56 shows the effectiveness of the AGC loop in
maintaining a baseband amplifier output amplitude with less
than 0.5 dB of amplitude error over an IF input range of 40 dB
while demodulating a QPSK-modulated signal at 380 MHz.
The AD8362 is insensitive to crest factor variations and
therefore provides similar performance regardless of the
modulation of the incoming signal.
IFIP POWER INPUT (dBm, Z
O
= 200Ω)
I CHANNEL VOL
T
AGE OUTPUT
(IOPP – IOPN) (mV rms)
ERROR (dB)
–55 –45
70
90
80
120
110
100
140
130
–4
–2
–3
1
0
–1
3
2
–35 –25 –15 –5 5
QPSK
ERROR
03678-065
–5.1dBm re 10kΩ
Figure 56. AD8348 Baseband Amplifier Output vs.
IF Input Power with AD8362 AGC Loop
BASEBAND FILTERS
Baseband low-pass or band-pass filtering can be conveniently
performed between the mixer outputs (IMXO and QMXO) and
the input to the baseband amplifiers. Consideration should be
given to the output impedance of the mixers (40 Ω).
L2
1.2µH
AD8348
IMXO VCMO IAIN
R1
60Ω
L1
0.68µH
C5
150pF
C6
82pF
R2
100Ω
C1
4.7pF
C2
8.2pF
03678-056
TO AD8362
INPUT IF AGC
LOOP IS USED
Figure 57. Baseband Filter Schematic
Figure 57 shows the schematic for a 100 Ω, fourth-order elliptic
low-pass filter with a 3 dB cutoff frequency of 20 MHz. Source
and load impedances of approximately 100 Ω ensure that the
filter sees a matched source and load. This also ensures that the
mixer output is driving an overall load of 200 Ω. Note that the
shunt termination resistor is tied to the source driving VCMO
and not to ground. This ensures that the input to the baseband
amplifier is biased to the proper reference level. VCMO is not
an output pin and must be biased by a low impedance source.
The frequency response and group delay of this filter are shown
in Figure 58 and Figure 59.
FREQUENCY (MHz)
A
TTENU
A
TION (dB)
1
–80
–50
–40
–60
–70
–30
–20
–10
0
10 100
03678-057
Figure 58. Baseband Filter Response
FREQUENCY (MHz)
GROUP DEL
A
Y (ns)
1
0
15
20
10
5
25
30
35
40
45
50
10 100
03678-058
12
Figure 59. Baseband Filter Group Delay
AD8348
Rev. A | Page 23 of 28
LO GENERATION
Analog Devices has a line of PLLs that can be used for
generating the LO signal. Table 4 lists the PLLs and their
maximum frequency and phase noise performance.
Table 4. ADI PLL Selection Table
ADI Model
Frequency FIN
(MHz)
@ 1 kHz ΦN
dBc/Hz,
200 kHz PFD
ADF4001BRU 165 −99
ADF4001BCP 165 −99
ADF4110BRU 550 −91
ADF4110BCP 550 −91
ADF4111BRU 1200 −78
ADF4111BCP 1200 −78
ADF4112BRU 3000 −86
ADF4112BCP 3000 −86
ADF4116BRU 550 −89
ADF4117BRU 1200 −87
ADF4118BRU 3000 −90
ADI also offers the ADF4360 fully integrated synthesizer and
VCO on a single chip that offers differential outputs for driving
the local oscillator input of the AD8348. This means that the user
can eliminate the use of a balun for single-ended-to-differential
conversions. The ADF4360 comes as a family of chips with six
operating frequency ranges. One can be chosen depending on
the local oscillator frequency required. Table 5 shows the
options available.
Table 5. ADF4360 Family Operating Frequencies
ADI Model Output Frequency Range (MHz)
ADF4360-1 2150 to 2450
ADF4360-2 1800 to 2150
ADF4360-3 1550 to 1950
ADF4360-4 1400 to 1800
ADF4360-5 1150 to 1400
ADF4360-6 1000 to 1250
ADF4360-7 Lower frequencies set by external L
EVALUATION BOARD
Figure 60 shows the schematic for the AD8348 evaluation
board. Note that uninstalled components are indicated with the
OPEN designation. The board is powered by a single supply in
the range of 2.7 V to 5.5 V. Table 6 details the various configu-
ration options of the evaluation board. Table 7 shows the various
jumper configurations for operating the evaluation board with
different signal paths.
Power to operate the board can be fed to a single VS test point
located near the LO input port at the top of the evaluation
board. A GND test point is conveniently provided next to the
VS test point for the return path.
The device is enabled by moving Switch SW11 (at the bottom left
of the evaluation board) to the ENBL position. The device is
disabled by moving SW11 to the DENBL position. If desired, the
device can be enabled and disabled from an external source that
can be fed into the ENBL SMA connector or the VENB test point,
in which case SW11 should be placed in the DENBL position.
The IF and MX inputs are selected via SW12. The switch should
be moved in the direction of the desired input.
Gain Control
For convenience, a potentiometer, R15, is provided to allow for
changes in gain without the need for an additional dc voltage
source. To use the potentiometer, the SW13 switch must be set
to the POT position. Alternatively, an external voltage applied
to either the test point or SMA connector labeled VGIN can set
the gain. SW13 must be set to the EXT position when an
external gain control voltage is used.
LO Input
The local oscillator signal should be fed to the SMA Connector
J21. This port is terminated in 50 Ω. The acceptable LO power
input range is from −12 dBm to 0 dBm and must be at a
frequency double that of the IF/MX frequency. Remember that
the AD8348 uses a 2:1 frequency divider in the LO path to
generate the internally required quadrature-phase-related LO
signals.
IF Input
The IF input should be fed into the SMA connector IFIP. The
VGA must be enabled when this port is used (SW12 in the IF
position). When this IF input is chosen, the signal path includes
a minimum-loss attenuator to transform a 50 Ω input source to
the 200 Ω source impedance level for which the VGA was
designed. This pad provides a very broadband input match at
the expense of an 11.46 dB power attenuation in the input path.
It is very important to take this into account when measuring
the noise and distortion performance of the unmodified board
using the IFIP input; the apparent noise figure will be degraded
by 11.46 dB, and the apparent IIP3 will be 11.46 dB higher than
actual. If full weak-signal performance is desired from the
evaluation board, the attenuator (comprising R31 and R32)
should be removed and replaced with a low-loss RF transformer
providing the desired 4:1 impedance ratio. When a transformer
is used, IFIN should be ac-coupled to ground and not driven
differentially with IFIP.
MX Input
The evaluation board is by default set for a differential MX drive
through a balun (T41) from a single-ended source fed into the
MXIP SMA connector. When the MX inputs are used, the
internal VGA is bypassed. To change to a differential driving
source, T41 should be removed along with Resistor R42. The
0 Ω R43 and R44 resistors should be installed in place of T41 to
bridge the gap between the input traces. This presents a nominal
AD8348
Rev. A | Page 24 of 28
differential impedance of 200 Ω (100 Ω per side). The
differential inputs should then be fed into SMA connectors
MXIP and MXIN.
Mixer Outputs
The I and Q mixer outputs are available through the IMXO and
QMXO SMA connectors. These outputs are biased to VCMO
and are not designed to drive loads smaller than 200 Ω. To
prevent damage to test equipment that cannot tolerate dc biases,
pads for series dc-blocking capacitors are provided. These pads
are populated with 0 Ω by default.
Baseband Outputs
The baseband outputs are made available at the IOPP, IOPN,
QOPP, and QOPN test points and SMA connectors. These
outputs are not designed to be connected directly to 50 Ω loads
and should be presented with loads of approximately 2 kΩ or
greater.
The dc bias level of the baseband amplifier outputs are by
default tied to VREF through LK11. If desired, the dc bias level
can be changed by removing LK11 and driving a dc voltage
onto the VCMO test point.
L3I
OPEN
L2I
OPEN
L1I
OPEN
R2I
OPEN
R1I
OPEN
C7I
OPEN
C6I
OPEN
C5I
OPEN
C4I
OPEN
C3I
OPEN
C2I
OPEN
C1I
OPEN
LK2I
VCMO
J1I
IMXO
C13
0.1µF
LK1I
VCMO
LK11
LK4I
LK3I
C10I
0Ω
C32
1000pF
C31
1000pF
R31
57.6Ω
13
54
J21
LO
C21
1000pF
C22
1000pF
R21
60.4Ω
+V
S
C51
100pF
C52
0.1µF
+V
S
C53
100pF
C54
0.1µF
+V
S
MXIN
MXIP
R42
0Ω
R44
OPEN
R43
OPEN
C42
1000pF
C43
1000pF
SW13
C12
0.1µF
R13
OPEN
J3I
IOPN
J2I
IOPP
R5I
0Ω
R4I
0Ω
IOPN
IOPP
GND C9I
OPEN
C8I
OPEN
C0I
0.1µF
C0Q
0.1µF
C11
4.7µF
IFIP
EXT
POT
R14
10kΩ
LK5I LK5Q
+V
S
IOFS QOFS
ENBL
VENB
R3I
49.9Ω
R12
10kΩ
R11
49.9Ω
ENBL
DENBL
SW11
VREF
R32
174Ω
T21
ETC1-1-13
AD8348
IMXO
L3Q
OPEN
L2Q
OPEN
L1Q
OPEN
R2Q
OPEN
R1Q
OPEN C7Q
OPEN
C6Q
OPEN
C5Q
OPEN
C4Q
OPEN
C3Q
OPEN
C2Q
OPEN
C1Q
OPEN
LK2Q
VCMO
VCMO
J1Q
QMXO
LK1Q
LK4Q
LK3Q
C10Q
0Ω
R3Q
49.9Ω
QMXO
SW12
J3Q
QOPN
J2Q
QOPP
R5Q
0Ω
R4Q
0Ω
QOPN
QOPP
GND
GND
C9Q
OPEN
C8Q
OPEN
+V
S
IF MX
C55
100pF
C55
0.1µF
R41
OPEN
VGIN
R15
10kΩ
POT
T41
ETK4-2T
C41
1µF
03678-059
IFIP MXIP
VPOS2 VGIN
IOFS QOFS
VREF ENBL
LOINLOIP
VPOS1 COM1
IOPN QOPN
IOPP QOPP
VCMO ENVG
IAIN QAIN
COM3 COM3
IMXO QMXO
COM2 VPOS3
IFIN MXIN
18
17
16
15
28
27
26
25
24
23
22
21
20
19
11
12
13
14
1
2
3
4
5
6
7
8
9
10
Figure 60. Evaluation Board Schematic
AD8348
Rev. A | Page 25 of 28
03678-060
AD8348
Rev. A | Page 26 of 28
03678-062
Figure 63. Evaluation Board Bottom Layer
03678-063
Figure 64. Evaluation Board Bottom Silkscreen
AD8348
Rev. A | Page 27 of 28
Table 6. Evaluation Board Configuration Options
Component Function Default Condition
VS, GND Power supply and ground vector pins. Not applicable
SW11, ENBL Device enable: Place SW11 in the ENBL position to connect the ENBL pin to VS. Place SW11 in
the DENBL position to disable the device by grounding the Pin ENBL through a 50 Ω pull-down
resistor. The device can also be enabled via an external voltage applied to ENBL or VENB.
SW11 = ENBL
SW13, R15,
VGIN
Gain control selection: With SW13 in the POT position, the gain of the VGA can be set using the
R15 potentiometer. With SW13 in the EXT position, the VGA gain can be set by an external
voltage to the SMA connector VGIN. For VGA operation, the VGA must first be enabled by
setting SW12 to the IF position.
SW13 = POT
SW12 VGA enable selection: With SW12 in the IF position, the ENVG pin is connected to VS and the
VGA is enabled. The IF input should be used when SW12 is in the IF position. With SW12 in the
MX position, the ENVG pin is grounded and the VGA is disabled. The MX inputs should be used
when SW12 is in the MX position.
SW12 = IF
IFIP, R31, R32 IF inputs: The single-ended IF signal should be connected to this SMA connector. R31 and R32
form an L pad that presents a 50 Ω termination to the driving source. This L pad introduces an
11.46 dB loss in the input signal path and should be taken into consideration when calculating
the gain of the AD8348.
R31 = 57.6 Ω
R32 = 174 Ω
MXIP, MXIN,
T41,
R41, R42,
C42, C43
Mixer inputs: These inputs can be configured for either differential or single-ended operation.
The evaluation board is by default set for differential MX drive through a balun (T41) from a
single-ended source fed into the MXIP SMA connector. To change to a differential driving source,
T41 should be removed along with Resistor R42. The 0 Ω Resistors R43 and R44 should be installed in
place of T41 to bridge the gap between the input traces. This will present a nominal differential
impedance of 200 Ω (100 Ω per side). The differential inputs should then be fed into SMA
connectors MXIP and MXIN.
T41 = M/A-COM ETK4-2T;
R41= OPEN; C42, C43 =
1000 pF; R42 = 0 Ω
LK11, VCMO Baseband amplifier output bias: Installing LK11 connects VREF to VCMO. This sets the bias level
on the baseband amplifiers to VREF, which is equal to approximately 1 V. Alternatively, with
LK11 removed, the bias level of the baseband amplifiers can be set by applying an external
voltage to the VCMO test point.
LK11 installed
C8, C9, R4, R5
(I and Q)
Baseband amplifier outputs and output filter: Additional low-pass filtering can be provided at
the baseband output with these filters.
R4, R5 = 0 Ω
C10 (I and Q) Mixer output dc-blocking capacitors: The mixer outputs are biased to VCMO. To prevent
damage to test equipment that cannot tolerate dc biases, C10 is provided to block the dc
component, thus protecting the test equipment.
C10 = 0 Ω
C1 to C7,
R1, R2,
L1 to L3
(I and Q)
Baseband filter: These components are provided for baseband filtering between the mixer
outputs and the baseband amplifier inputs. The baseband amplifier input impedance is high
and the filter termination impedance is set by R2. See Table 7 for the jumper settings.
All = OPEN
LK5 (I and Q) Offset compensation loop disable: Installing these jumpers will disable the offset compensation
loop for the corresponding channel.
LK5x = OPEN
Table 7. Filter-Jumper Configuration Options
Condition LK1x LK2x LK3x LK4x
xMXO to xAIN Directly • •
xMXO to xAIN via Filter • •
xMXO to J1x Directly, xAIN Unused • •
xMXO to J1x via Filter, xAIN Unused • •
Drive xAIN from J1x •
AD8348
Rev. A | Page 28 of 28
OUTLINE DIMENSIONS
28 15
141
8°
0°
COMPLIANT TO JEDEC STANDARDS MO-153AE
SEATING
PLANE
COPLANARITY
0.10
1.20 MAX
6.40 BSC
0.65
BSC
PIN 1
0.30
0.19 0.20
0.09
4.50
4.40
4.30
0.75
0.60
0.45
9.80
9.70
9.60
0.15
0.05
Figure 65. 28-Lead Thin Shrink Small Outline Package [TSSOP]
(RU-28)
Dimensions shown in millimeters
ORDERING GUIDE
Model Temperature Range Package Description Package Option
AD8348ARU −40°C to +85°C 28-Lead Thin Shrink Small Outline Package [TSSOP] RU-28
AD8348ARU-REEL7 −40°C to +85°C 28-Lead Thin Shrink Small Outline Package [TSSOP] 7” Tape and Reel RU-28
AD8348ARUZ1−40°C to +85°C 28-Lead Thin Shrink Small Outline Package [TSSOP] RU-28
AD8348ARUZ-REEL71−40°C to +85°C 28-Lead Thin Shrink Small Outline Package [TSSOP] 7” Tape and Reel RU-28
AD8348-EVAL Evaluation Board
1 Z = Pb-free part.
©2006 Analog Devices, Inc. All rights reserved. Trademarks and
registered trademarks are the property of their respective owners.
C03678-0-4/06(A)
