Figure 1. ADS-946 Functional Block Diagram
FEATURES
14-bit resolution
8MHz guaranteed sampling rate
No missing codes over full military temperature range
Ideal for both time and frequency-domain applications
Excellent THD (75dB) and SNR (77dB)
Edge-triggered; No pipeline delays
Small, 24-pin, ceramic DDIP or SMT
Requires only ±5V supplies
Low-power, 2 Watts
MIL-STD-883 screening optional
GENERAL DESCRIPTION
The low-cost ADS-946 is a 14-bit, 8MHz sampling A/D
converter. This device accurately samples full-scale input
signals up to Nyquist frequencies with no missing codes.
Excellent differential nonlinearity error (DNL), signal-to-noise
ratio (SNR), and total harmonic distortion (THD) make the
ADS-946 the ideal choice for both time-domain (CCD/FPA
imaging, scanners, process control) and frequency-domain
(radar, telecommunications, spectrum analysis) applications.
The functionally complete ADS-946 contains a fast-settling
sample-hold amplifier, a subranging (two-pass) A/D converter,
an internal reference, timing/control logic, and error-correction
circuitry. Digital input and output levels are TTL. The
ADS-946 only requires the rising edge of a start convert
pulse to operate.
Requiring only ±5V supplies, the ADS-946 typically dissipates
just 2 Watts. The device is offered with a bipolar input range
of ±2V. Models are available for use in either commercial
(0 to +70°C) or military (–55 to +125°C) operating
®
®
INNOV A TION and EX CELLENCE
temperature ranges. A proprietary, auto-calibrating, error-
correcting circuit allows the device to achieve specified
performance over the full military temperature range.
INPUT/OUTPUT CONNECTIONS
PIN FUNCTION PIN FUNCTION
1BIT 1 (MSB) 24 ANALOG GROUND
2BIT 2 23 OFFSET ADJUST
3BIT 3 22 +5V ANALOG SUPPLY
4BIT 4 21 ANALOG INPUT
5BIT 5 20 –5V SUPPLY
6BIT 6 19 ANALOG GROUND
7BIT 7 18 START CONVERT
8BIT 8 17 EOC
9BIT 9 16 BIT 14 (LSB)
10 BIT 10 15 BIT 13
11 BIT 11 14 DIGITAL GROUND
12 BIT 12 13 +5V DIGITAL SUPPLY
ADS-946
14-Bit, 8MHz
Sampling A/D Converters
REF DAC
REGISTERREGISTER
OUTPUT REGISTER
16 BIT 14 (LSB)
15 BIT 13
12 BIT 12
11 BIT 11
10 BIT 10
9 BIT 9
8 BIT 8
7 BIT 7
6 BIT 6
5 BIT 5
4 BIT 4
3 BIT 3
2 BIT 2
1 BIT 1 (MSB)
TIMING AND
CONTROL LOGIC
OFFSET ADJUST 23
ANALOG INPUT 21
START CONVERT 18
EOC 17
+5V ANALOG SUPPLY 22
+5V DIGITAL SUPPLY 13
–5V SUPPLY 20
ANALOG GROUND 19, 24
DIGITAL GROUND 14
+S/H
BUFFER
DIGITAL CORRECTION LOGIC
FLASH
ADC
1
FLASH
ADC
2
POWER AND GROUNDING
Σ
AMP
DATEL, Inc., 11 Cabot Boulevard, Mansfield, MA 02048 (U.S.A.) Tel: (508)339-3000 Fax: (508)339-6356 For immediate assistance: (800) 233-2765
ADS-946
2
® ®
PARAMETERS MIN. TYP. MAX. UNITS
Operating Temp. Range, Case
ADS-946MC, GC 0+70 °C
ADS-946MM, GM, 883, G/883 –55 +125 °C
Thermal Impedance
θjc 6°C/Watt
θca 23 °C/Watt
Storage Temperature Range –65 +150 °C
Package Type 24-pin, metal-sealed, ceramic DDIP or SMT
Weight 0.42 ounces (12 grams)
ABSOLUTE MAXIMUM RATINGS
PARAMETERS LIMITS UNITS
+5V Supply (Pins 13, 22) 0 to +6 Volts
–5V Supply (Pin 20) 0 to –6 Volts
Digital Input (Pin 18) –0.3 to +VDD +0.3 Volts
Analog Input (Pin 21) ±5 Volts
Lead Temperature (10 seconds) +300 °C
PHYSICAL/ENVIRONMENTAL
+25°C 0 to +70°C 55 to +125°C
ANALOG INPUT MIN. TYP. MAX. MIN. TYP. MAX. MIN. TYP. MAX. UNITS
Input Voltage Range ±2 ±2 ——±2 Volts
Input Resistance 200 200 200
Input Capacitance 615 615 615 pF
DIGITAL INPUT
Logic Levels
Logic "1" +2.0 +2.0 +2.0 Volts
Logic "0" +0.8 +0.8 +0.8 Volts
Logic Loading "1" +20 +20 +20 µA
Logic Loading "0" –20 –20 –20 µA
Start Convert Positive Pulse Width 10 20 10 20 10 20 ns
STATIC PERFORMANCE
Resolution 14 14 ——14 Bits
Integral Nonlinearity (fin = 10kHz) ±0.75 ±0.75 ——±1 LSB
Differential Nonlinearity (fin = 10kHz) –0.95 ±0.5 +1.25 –0.95 ±0.5 +1.25 –0.95 ±0.75 +1.99 LSB
Full Scale Absolute Accuracy ±0.15 ±0.4 ±0.15 ±0.4 ±0.4 ±0.8 %FSR
Bipolar Zero Error (Tech Note 2) ±0.2 ±0.4 ±0.2 ±0.4 ±0.4 ±0.65 %FSR
Gain Error (Tech Note 2) ±0.2 ±0.75 ±0.2 ±0.75 ±0.4 ±1.25 %
No Missing Codes (fin = 10kHz) 14 14 14 Bits
DYNAMIC PERFORMANCE
Peak Harmonics (–0.5dB)
dc to 500kHz 76 –72 76 –72 –74 –70 dB
500kHz to 1MHz –75 –72 –75 –72 –74 68 dB
1MHz to 4MHz –75 –71 –75 –71 –69 65 dB
Total Harmonic Distortion (–0.5dB)
dc to 500kHz 75 –71 75 –71 –74 –70 dB
500kHz to 1MHz –75 –70 –75 –70 –72 68 dB
1MHz to 4MHz –75 70 –75 70 69 64 dB
Signal-to-Noise Ratio
(w/o distortion, –0.5dB)
dc to 500kHz 73 77 73 77 72 76 dB
500kHz to 1MHz 73 77 73 77 72 76 dB
1MHz to 4MHz 73 77 73 77 72 76 dB
Signal-to-Noise Ratio
(& distortion, –0.5dB)
dc to 500kHz 70 74 70 74 68 73 dB
500kHz to 1MHz 69 73 69 73 65 70 dB
1MHz to 4MHz 69 73 69 73 65 70 dB
Noise 150 150 150 µVrms
Two-Tone Intermodulation
Distortion (fin = 2.45MHz,
1.975MHz, fs = 8MHz, –0.5dB) –82 82 82 dB
Input Bandwidth (–3dB)
Small Signal (–20dB input) 30 30 ——30 MHz
Large Signal (–0.5dB input) 10 10 ——10 MHz
Feedthrough Rejection (fin = 4MHz) 85 85 85 dB
Slew Rate ±400 ±400 ±400 V/µs
Aperture Delay Time +5 +5 +5 ns
Aperture Uncertainty 2 2 2ps rms
FUNCTIONAL SPECIFICATIONS
(TA = +25°C, ±VDD = ±5V, 8MHz sampling rate, and a minimum 3 minute warmup unless otherwise specified.)
ADS-946
3
® ®
+25°C 0 to +70°C –55 to +125°C
DYNAMIC PERFORMANCE (Cont.) MIN. TYP. MAX. MIN. TYP. MAX. MIN. TYP. MAX. UNITS
S/H Acquisition Time
( to ±0.003%FSR, 4V step) 55 60 55 60 55 60 ns
Overvoltage Recovery Time 100 125 100 125 100 125 ns
A/D Conversion Rate 8 8 8 MHz
DIGITAL OUTPUTS
Logic Levels
Logic "1" +2.4 +2.4 ——+2.4 Volts
Logic "0" +0.4 +0.4 +0.4 Volts
Logic Loading "1" ——–4 –4 –4 mA
Logic Loading "0" +4 +4 +4 mA
Output Coding Offset Binary
POWER REQUIREMENTS
Power Supply Ranges
+5V Supply +4.75 +5.0 +5.25 +4.75 +5.0 +5.25 +4.9 +5.0 +5.25 Volts
–5V Supply –4.75 –5.0 –5.25 –4.75 –5.0 –5.25 –4.9 –5.0 –5.25 Volts
Power Supply Currents
+5V Supply +250 +270 +250 +270 +250 +270 mA
–5V Supply –150 –170 –150 –170 –150 –170 mA
Power Dissipation 22.2 22.2 22.2 Watts
Power Supply Rejection ±0.05 ±0.05 ±0.05 %FSR/%V
Footnotes:
This is the time required before the A/D output data is valid once the analog input
is back within the specified range. This time is only guaranteed if the input does
not exceed ±2.2V (S/H saturation voltage).
The minimum supply voltages of +4.9V and –4.9V for ±VDD are required for
–55°C operation only. The minimum limits are +4.75V and –4.75V when
operating at +125°C
6.02
(SNR + Distortion) – 1.76 + 20 log Full Scale Amplitude
Actual Input Amplitude
All power supplies should be on before applying a start convert pulse. All
supplies and the clock (start convert pulses) must be present during warmup
periods. The device must be continuously converting during this time.
Contact DATEL for other input voltage ranges.
An 8MHz clock with a 20nsec positive pulse width is used for all production
testing. See Timing Diagram, Figure 4, for more details.
Effective bits is equal to:
3. Applying a start convert pulse while a conversion is in
progress (EOC = logic 1) will initiate a new and inaccurate
conversion cycle. Data for the interrupted and subsequent
conversions will be invalid.
4. A passive bandpass filter is used at the input of the A/D for
all production testing.
Figure 2. Optional ADS-946 Gain Adjust Calibration Circuit
TECHNICAL NOTES
1. Obtaining fully specified performance from the ADS-946
requires careful attention to pc card layout and power
supply decoupling. The device’s analog and digital ground
systems are connected to each other internally. For optimal
performance, tie all ground pins (14, 19 and 24) directly to a
large analog ground plane beneath the package.
Bypass all power supplies to ground with 4.7µF tantalum
capacitors in parallel with 0.1µF ceramic capacitors. Locate
the bypass capacitors as close to the unit as possible.
2. The ADS-946 achieves its specified accuracies without the
need for external calibration. If required, the device’s small
initial offset and gain errors can be reduced to zero using
the adjustment circuitry shown in Figures 2 and 3. When
using this circuitry, or any similar offset and gain calibration
hardware, make adjustments following warmup. To avoid
interaction, always adjust offset before gain.
To Pin 21
of ADS-946
–5V
SIGNAL
INPUT
GAIN
ADJUST
1.98k
50
+5V
2k
ADS-946
4
® ®
CALIBRATION PROCEDURE
Any offset and/or gain calibration procedures should not be
implemented until devices are fully warmed up. To avoid
interaction, offset must be adjusted before gain. The ranges of
adjustment for the circuits in Figures 2 and 3 are guaranteed
to compensate for the ADS-946's initial accuracy errors and
may not be able to compensate for additional system errors.
A/D converters are calibrated by positioning their digital
outputs exactly on the transition point between two adjacent
digital output codes. This can be accomplished by connecting
LED’s to the digital outputs and adjusting until certain LED's
"flicker" equally between on and off. Other approaches
employ digital comparators or microcontrollers to detect when
the outputs change from one code to the next.
Offset adjusting for the ADS-946 is normally accomplished at
the point where the MSB is a 1 and all other output bits are 0’s
and the LSB just changes from a 0 to a 1. This digital output
transition ideally occurs when the applied analog input is
+½ LSB (+122µV).
Gain adjusting is accomplished when all bits are 1's and the
LSB just changes from a 1 to a 0. This transition ideally
occurs when the analog input is at +full scale minus 1½ LSB's
(+1.99963V).
Zero/Offset Adjust Procedure
1. Apply a train of pulses to the START CONVERT input
(pin 18) so the converter is continuously converting.
2. Apply +122µV to the ANALOG INPUT (pin 21).
3. Adjust the offset potentiometer until the output bits are
10 0000 0000 0000 and the LSB flickers between 0 and 1.
Figure 3. Typical ADS-946 Connection Diagram
Gain Adjust Procedure
1. Apply +1.99963V to the ANALOG INPUT (pin 21).
2. Adjust the gain potentiometer until all output bits are 1's
and the LSB flickers between 1 and 0.
3. To confirm proper operation of the device, vary the input
signal to obtain the output coding listed in Table 2.
BIPOLAR INPUT VOLTAGE OFFSET BINARY
SCALE (±2V RANGE) MSB LSB
+FS –1 LSB +1.99976 11 1111 1111 1111
+3/4 FS +1.50000 11 1000 0000 0000
+1/2 FS +1.00000 11 0000 0000 0000
00.00000 10 0000 0000 0000
–1/2 FS –1.00000 01 0000 0000 0000
–3/4 FS –1.50000 00 1000 0000 0000
–FS +1 LSB –1.99976 00 0000 0000 0001
–FS –2.00000 00 0000 0000 0000
Table 2. Output Coding for Bipolar Operation
INPUT VOLTAGE ZERO ADJUST GAIN ADJUST
RANGE +½ LSB +FS –1½ LSB
±2V +122µV +1.99963V
Table 1. Gain and Zero Adjust
0.1µF0.1µF
4.7µF 4.7µF
22, 13
24
2019
ADS-946
–5V
20k
0.1µF
4.7µF
+5V
14
–5V
+5V
21
23
18
1
2
3
4
5
6
7
8
9
10
11
12
15
16
17
BIT 1 (MSB)
BIT 2
BIT 3
BIT 4
BIT 5
BIT 6
BIT 7
BIT 8
BIT 9
BIT 10
BIT 11
BIT 12
BIT 13
BIT 14 (LSB)
EOC
ANALOG
INPUT
START
CONVERT
A single +5V supply should be used for both the +5V analog and +5V digital.
If separate supplies are used, the difference between the two cannot exceed 100mV.
+ + +
ZERO/
OFFSET
ADJUST
ADS-946
5
® ®
Electrically-insulating, thermally-conductive "pads" may be
installed underneath the package. Devices should be soldered
to boards rather than socketed, and of course, minimal air flow
over the surface can greatly help reduce the package
temperature.
In more severe ambient conditions, the package/junction
temperature of a given device can be reduced dramatically
(typically 35%) by using one of DATEL's HS Series heat sinks.
See Ordering Information for the assigned part number. See
page 1-183 of the DATEL Data Acquisition Components
Catalog for more information on the HS Series. Request DATEL
Application Note AN-8, "Heat Sinks for DIP Data Converters," or
contact DATEL directly, for additional information.
THERMAL REQUIREMENTS
All DATEL sampling A/D converters are fully characterized
and specified over operating temperature (case) ranges of
0 to +70°C and 55 to +125°C. All room-temperature
(TA = +25°C) production testing is performed without the use
of heat sinks or forced-air cooling. Thermal impedance
figures for each device are listed in their respective
specification tables.
These devices do not normally require heat sinks, however,
standard precautionary design and layout procedures should
be used to ensure devices do not overheat. The ground and
power planes beneath the package, as well as all pcb signal
runs to and from the device, should be as heavy as possible
to help conduct heat away from the package.
Figure 4. ADS-946 Timing Diagram
Notes:
1. Scale is approximately 5ns per division. Sampling rate = 8MHz.
2. The start convert positive pulse width must be between 10 and 50ns or between 80 and 110ns (when sampling at 8MHz)
to ensure proper operation. For sampling rates less than 8MHz, the start pulse can be wider than 110nsec, however a
minimum pulse width low of 15nsec should be maintained. An 8MHz clock with a 20nsec positive pulse width is used
for all production testing.
START
CONVERT
INTERNAL S/H
NN+1
20ns
typ.
25ns typ.
Acquisition Time
55ns typ.
60ns max.
Hold
10ns typ.
EOC
20ns typ.
Conversion Time
78ns min., 85ns typ., 90ns max.
OUTPUT
DATA Data N-1 Valid Data N Valid
30ns typ.
Invalid Data
95ns typ.
70ns typ.
10ns typ.
ADS-946
6
® ®
Figure 6. ADS-946 Histogram and Differential Nonlinearity
Figure 5. FFT Analysis of ADS-946
DNL (LSB's)
Codes
016,384
–0.57
+0.81
0
16,384
Digital Output Code
Number of Occurrences
0
–10
–20
–30
–40
–50
–60
–70
–80
–90
–100
–110
–120
–130
–140
–150
Amplitude Relative to Full Scale (dB)
Frequency
(fs = 8MHz, fin = 3.85MHz, Vin = –0.5dB, 16,384-point FFT)
0 400 800 1.2 1.6 2.0 2.4 2.8 3.2 3.6 4.0
kHz kHz MHz MHz MHz MHz MHz MHz MHz MHz
ADS-946
7
® ®
GND
Q
CLR
CK
D
PR
+5VF
+5VA
+15V
–15V
-15V
+15V
–5VA
+5V
–5V
+5VF
-15V
-5VA
OPTION
+5VF
Q
PR
D
CK
CLR
+5VF
+5VF
+5VF
+5V
–5V
+5VA
BIT12
BIT11
BIT10
BIT9
BIT8
BIT7
BIT6
BIT5
BIT4
BIT3
BIT2
BIT1
ADS-946
+5VD
DGND
BIT13
BIT14
EOC
TRIG
AGND
-5V
AIN
+5VA
OFFSET
AGND
Q1
Q2
Q3
Q4
Q5
Q6
Q7
Q8
8D
7D
6D
5D
4D
3D
2D
1D
+
+
+
+
+
+
+
+5VA+15V
+
+
+
+
+
C15
U6
P2
SG10
SG3
SG2
SG1
C14
C7
C13
C6
C12C5
L7
L6
R1
C20
C4 C11
L5
L4
L3
C3 C10
C2 C9
L2
C8C1
L1
P4
C19
SG8SG7
U4
R2 C18
SG5 SG6
SG4
R3
C26 C27 C25
SG9
C24
C23
C16
C22
C17
C21
X1 U6
P3
JPR1
U5
P1
JPR2
U5
U1
U3
OFFSET
ADJUST
ANA. IN
IN
ANA. CLC402
HI2541
ANA. IN
START CONVERT
7
8
14
CONV.
START
74HCT86
B14
B13
B12
B11
B10
B9
B8
B7
B6
B5
B4
B3
B2
B1
TRIG
74HCT86
74HCT573
74HCT573
74HCT86
HCT7474
20µH
20µH
20k
20µH
20µH
20µH
20µH
20µH
HCT7474
8MHz
CRYSTAL
15pF 3.2k
2.2µF
4
56
13
12 14 11
7
9
8
13
11
12
10
26
24
22
25
23
21
19
17
15
13
11
9
7
5
3
1
20
18
16
14
12
10
8
6
4
2
2
5
411 10
14
5
6
4
2
3
1
7
231
2
13
33
31
34
32
30
28
26
24
22
20
18
16
14
12
10
8
6
4
2
29
27
25
23
21
19
17
15
13
11
9
7
5
3
1
23
1
9
10
8
1
2
3
4
5
6
7
8
9
10
11
12
24
23
22
21
20
19
18
17
16
15
14
13
10
1
12
13
14
15
16
17
18
19
20
2
3
4
5
6
7
8
9
11
SPARE GATES
C1 - C7 ARE 20V.
2. CLOSE SG1-SG3, SG9, SG10.
ALL RESISTORS ARE IN OHMS.
1. UNLESS OTHERWISE SPECIFIED ALL CAPACITORS ARE 50V.
NOTES:
OE
CE
Q1
Q2
Q3
Q4
Q5
Q6
Q7
Q8
8D
7D
6D
5D
4D
3D
2D
1D
U2
10
12
13
14
15
16
17
18
19
20
2
3
4
5
6
7
8
9
11 OE
CE 1
CE
0.1µF
0.1µF
0.1µF
0.1µF
0.1µF
2.2µF
0.1µF
2.2µF
2.2µF
0.1µF
2.2µF
2.2µF
2.2µF
2.2µF
2.2µF
2.2µF
2.2µF
6
+5VF
(Optional) (Optional)
(Optional)
(Optional)
0.01µF
0.01µF
0.01µF
0.01µF
0.01µF
0.01µF
0.01µF
0.1µF
U5
U5
Q
3. SEE DATEL DWG A-24546 FOR ADDITIONAL INFORMATION
ON ADS-B946 EVALUATION BOARD.
ADS-946
MECHANICAL DIMENSIONS INCHES (mm)
24-Pin DDIP
Versions
ADS-946MC
ADS-946MM
ADS-946/883
ORDERING INFORMATION
ACCESSORIES
ADS-B946 Evaluation Board (without ADS-946)
HS-24 Heat Sink for all ADS-946 DDIP models
24-Pin
Surface Mount
Versions
ADS-946GC
ADS-946GM
ADS-946G/883
Receptacles for pc board mounting can be ordered through AMP, Inc., Part # 3-331272-8 (Component Lead
Socket), 24 required. For MIL-STD-883 product specifcation, contact DATEL.
® ®
OPERATING 24-PIN
MODEL TEMP. RANGE PACKAGE
ADS-946MC 0 to +70°C DDIP
ADS-946MM –55 to +125°C DDIP
ADS-946/883 –55 to +125°C DDIP
ADS-946GC 0 to +70°C SMT
ADS-946GM –55 to +125°C SMT
ADS-946G/883 –55 to +125°C SMT
DATEL makes no representation that the use of its products in the circuits described herein, or the use of other technical information contained herein, will not infringe upon existing or future patent rights. The descriptions contained herein
do not imply the granting of licenses to make, use, or sell equipment constructed in accordance therewith. Specifications are subject to change without notice. The DATEL logo is a registered DATEL, Inc. trademark.
® ®
ISO 9001
ISO
9001
REGISTERED
DS-0314 03/97
0.200 MAX.
(5.080)
0.235 MAX.
(5.969)
0.600 ±0.010
(15.240)
0.80 MAX.
(20.32)
0.100 TYP.
(2.540)
0.100
(2.540)
0.018 ±0.002
(0.457)
0.100
(2.540)
0.040
(1.016)
1.31 MAX.
(33.27)
112
13
24
1.100
(27.940)
0.190 MAX.
(4.826)
0.010
(0.254)
+0.002
–0.001
SEATING
PLANE
0.025
(0.635)
Dimension Tolerances
(unless otherwise indicated):
2 place decimal (.XX) ±0.010 (±0.254)
3 place decimal (.XXX) ±0.005 (±0.127)
Lead Material: Kovar alloy
Lead Finish: 50 microinches (minimum)
gold plating over 100 microinches
(nominal) nickel plating
0.80 MAX.
(20.32)
0.015
(0.381)
MAX. radius
for any pin
1.31 MAX.
(33.02)
0.100 TYP.
(2.540)
0.100
(2.540)
0.190 MAX.
(4.826)
0.040
(1.016)
0.020 TYP.
(0.508)
0.020
(0.508)
24 13
121
PIN 1
INDEX 0.130 TYP.
(3.302)
Dimension Tolerances (unless otherwise indicated):
2 place decimal (.XX) ±0.010 (±0.254)
3 place decimal (.XXX) ±0.005 (±0.127)
Lead Material: Kovar alloy
Lead Finish: 50 microinches (minimum) gold plating
over 100 microinches (nominal) nickel plating
0.060 TYP.
(1.524)
0.010 TYP.
(0.254)
DATEL, Inc. 11 Cabot Boulevard, Mansfield, MA 02048-1151
Tel: (508) 339-3000 (800) 233-2765 Fax: (508) 339-6356
Internet: www.datel.com E-mail:sales@datel.com
Data Sheet Fax Back: (508) 261-2857
DATEL (UK) LTD. Tadley, England Tel: (01256)-880444
DATEL S.A.R.L. Montigny Le Bretonneux, France Tel: 1-34-60-01-01
DATEL GmbH München, Germany Tel: 89-544334-0
DATEL KK Tokyo, Japan Tel: 3-3779-1031, Osaka Tel: 6-354-2025