ADS-942

14-Bit, 2MHz

Sampling A/D Converters

FEATURES

14-bit resolution

2MHz minimum throughput

Functionally complete

Internal reference and sample/hold

-85dB total harmonic distortion

78dB signal-to-noise ratio

Full Nyquist-rate sampling

Small 32-pin DIP

Low-power, 2.9 Watts

GENERAL DESCRIPTION

DATEL's ADS-942 is a functionally complete, 14-bit, 2MHz,
sampling A/D converter. Its standard, 32-pin, triple-wide
ceramic DIP contains a fast-settling sample/hold amplifier, a
14-bit subranging (two-pass) A/D converter, a precision
reference, three-state output register and all the timing and
control logic necessary to operate from a single start
convert pulse.

The ADS-942 is optimized for wideband frequency-domain
applications and is fully FFT tested. The ADS-942 requires
±15V and +5V supplies and typically consumes 2.9 Watts.

INPUT/OUTPUT CONNECTIONS

+10V REF. OUT

START CONVERT

BIPOLAR

BIT 1 OUT (MSB)

ANALOG INPUT

BIT 1 OUT (MSB)

SIGNAL GROUND

BIT 2 OUT

OFFSET ADJUST

BIT 3 OUT

ANALOG GROUND

BIT 4 OUT

OVERFLOW

BIT 5 OUT

CODING SELECT

BIT 6 OUT

ENABLE

BIT 7 OUT

+5V SUPPLY

BIT 8 OUT

DIGITAL GROUND

BIT 9 OUT

+15V SUPPLY

BIT 10 OUT

15V SUPPLY

BIT 11 OUT

ANALOG GROUND

BIT 12 OUT

ANALOG GROUND

BIT 13 OUT

EOC

BIT 14 OUT (LSB)

PIN

FUNCTION

PIN

FUNCTION

Figure 1. ADS-942 Functional Block Diagram

REF

I
S

31 BIT 1 OUT (MSB)

30 BIT 1 OUT (MSB)

29 BIT 2 OUT

28 BIT 3 OUT

27 BIT 4 OUT

26 BIT 5 OUT

25 BIT 6 OUT

24 BIT 7 OUT

23 BIT 8 OUT

22 BIT 9 OUT

21 BIT 10 OUT

20 BIT 11 OUT

19 BIT 12 OUT

18 BIT 13 OUT

17 BIT 14 OUT (LSB)

TIMING AND

CONTROL LOGIC

+10V REF. OUT 1

START CONVERT 32

EOC 16

I
G

I
T

I
O

I
C

DAC

FLASH

ADC

BUFFER

ANALOG INPUT 3

SIGNAL

GROUND

DIGITAL

GROUND

+15V

SUPPLY

-
S

I
S

S/H

OFFSET
CIRCUIT

BIPOLAR 2

OFFSET ADJUST 5

+5V

SUPPLY

6, 14, 15

ANALOG

GROUND

CODING
SELECT

15V

SUPPLY

9 ENABLE

7 OVERFLOW

DATEL, Inc., 11 Cabot Boulevard, Mansfield, MA 02048-1151 (U.S.A.)

Tel: (508) 339-3000 Fax: (508) 339-6356

For immediate assistance: (800) 233-2765

ADS-942

FUNCTIONAL SPECIFICATIONS

= +25°C, ±V

= ±15V, +V

= +5V, 2MHz sampling rate, and a minimum 7 minute

warmup unless otherwise specified.)

ANALOG INPUTS

MIN.

TYP.

MAX.

UNITS

Input Voltage Range

Unipolar

0 to +10

Volts

Bipolar

±5

Volts

Input Impedence

4.9

Input Capacitance

DIGITAL INPUTS

Logic Levels

Logic "1"

+2.0

Volts

Logic "0"

+0.8

Volts

Logic Loading "1"

µA

Logic Loading "0"

600

µA

PERFORMANCE

Integral Non-Linearity
(f

= 1MHz)

+25°C

±1

±2

LSB

0 to +70°C

±1

±2

LSB

40 to +85°C

±2

±3

LSB

Differential Non-Linearity
(f

= 1MHz)

+25°C

0.75

±0.5

±0.75

LSB

0 to +70°C

0.95

±0.75

±1.25

LSB

40 to +85°C

±1

+2.5

LSB

Full Scale Absolute Accuracy

+25°C

±0.1

±0.122

%FSR

0 to +70°C

±0.12

±0.36

%FSR

40 to +85°C

±0.45

±0.85

%FSR

Unipolar Zero Error

+25°C (see Figure 3)

±0.05

±0.122

%FSR

0 to +70°C

±0.1

±0.2

%FSR

40 to +85°C

±0.2

±0.3

%FSR

Bipolar Zero Error

+25°C (see Figure 3)

±0.05

±0.122

%FSR

0 to +70°C

±0.1

±0.2

%FSR

40 to +85°C

±0.2

±0.3

%FSR

Bipolar Offset Error

+25°C (see Figure 3)

±0.1

±0.2

%FSR

0 to +70°C

±0.12

±0.3

%FSR

40 to +85°C

±0.5

±0.8

%FSR

Gain Error

+25°C (see Figure 3)

±0.018

±0.122

0 to +70°C

±0.12

±0.3

40 to +85°C

±0.6

±0.8

No Missing Codes (f

= 500kHz)

14 Bits

0 to +70°C

13 Bits

40 to +85°C

Resolution

14 Bits

OUTPUTS

MIN.

TYP.

MAX.

UNITS

Output Coding

Staight Bin./Offset Bin./2's Comp.
Comp. Bin./Comp. Offset Bin./C2C

Logic Level

Logic "1"

+2.4

Volts

Logic "0"

+0.4

Volts

Logic Loading "1"

160

µA

Logic Loading "0"

+6.4

Internal Reference

Voltage, +25°C

+9.98

+10.0

+10.02

Volts

Drift

±13

±30

ppm/°C

External Current

DYNAMIC PERFORMANCE

Total Harm. Distort. (0.5dB)

dc to 100kHz

100kHz to 500kHz

500kHz to 1MHz

Signal-to-Noise Ratio

(w/o distortion, 0.5dB
dc to 100kHz

100kHz to 500kHz

500kHz to 1MHz

Signal-to-Noise Ratio

(and distortion, 0.5dB)
dc to 100kHz

100kHz to 500kHz

500kHz to 1MHz

Spurious Free Dyn. Range

dc to 100kHz

100 to 500kHz

500kHz to 1MHz

Two-tone IMD
Distortion (f

= 100kHz,

240kHz, fs = 2.0Mhz,
0.5dB)

Input Bandwidth (3dB)

Small Signal (20dB input)

MHz

Large Signal (0.5dB input)

1.75

MHz

Slew Rate

±250

V/µs

Aperture Delay Time

±10

Aperature Uncertainty

ps, ms

S/H Acq. Time, (to ±0.003%FSR)

Sinusoidal (f

= 1MHz)

120

150

Step input

250

450

Conversion Rate

Sinusoidal (f

= 1MHz)

MHz

Step input

1.3

MHz

Feedthrough Rejection

= 1MHz)

Overvoltage Recovery, ±12V

1000

2000

Noise

250

µVrms

POWER REQUIREMENTS

Power Supply Ranges

+15V Supply

+14.25

+15.0

+15.75

Volts

15V Supply

14.25

15.0

15.75

Volts

+5V Supply

+4.75

+5.0

+5.25

Volts

Power Supply Currents

+15V Supply

+65

+87

15V Supply

+5V Supply

+150

+165

Power Dissipation

2.9

3.4

Watts

Power Supply Rejection

±0.02

%FSR%V

PHYSICAL/ENVIRONMENTAL

Operating Temp. Range, Case

ADS-942MC

+70

°C

ADS-942ME

+85

°C

Storage Temperature Range

+150

°C

Package Type

32-pin, metal-sealed, ceramic TDIP

Weight

0.46 ounces (13 grams)

ABSOLUTE MAXIMUM RATINGS

PARAMETERS

LIMITS

UNITS

+15V Supply (Pin 12)

0 to +16

Volts

15V Supply (Pin 13)

0 to 16

Volts

+5V Supply (Pin 10)

0 to +6

Volts

Digital Inputs (Pin 8,9, 32)

0.3 to +V

+0.3

Volts

Analog Input (Pin 3)

±15

Volts

Lead Temp. (10 seconds)

+300

°C

Footnote:

Same specification as In-Band Harmonics and Peak Harmonics.

ADS-942

For unipolar, adjust the zero trimpot so that the output code
flickers equally between 00 0000 0000 0000 and 00 0000
0000 0001 with CODING SELECT (pin 8) tied low (straight
binary) or between 11 1111 1111 1111 and 11 1111 1111
1110 with pin 8 tied high (complementary binary).

For bipolar operation, adjust the trimpot until the code
flickers equally between 10 0000 0000 0000 and 10 0000
0000 0001 with pin 8 tied low (offset binary) or between 01
1111 1111 1111 and 01 1111 1111 1110 with pin 8 tied high
(complementary offset binary).

Two's complement coding requires using BIT 1 OUT (MSB)
(pin 31). With pin 8 tied low, adjust the trimpot until the code
flickers between 00 0000 0000 0000 and 00 0000 0000
0001.

3. Full-Scale Adjustment

Set the output of the voltage reference used in step 2 to the
value shown in Table 2.

Table 2. Zero and Gain Adjustments

Input

Zero Adjust

Gain Adjust

Range

+1/2 LSB

FS 1½ LSB

0 to +10V

+305µV

+9.999085V

±5V

+305µV

+4.999085V

Adjust the gain trimpot until the output code flickers equally
between 11 1111 1111 1110 and 11 1111 1111 1111 with
pin 8 tied low for straight binary/offset binary or between 00
0000 0000 0000 and 00 0000 0000 0001 with pin 8 tied high
for complementary binary/complementary offset binary.

Two's complement coding requires using pin 31. With pin 8
tied low, adjust the gain trimpot until the output code flickers
equally between 01 1111 1111 1110 and 01 1111 1111
1111.

4. To confirm proper operation of the device, vary the precision

reference voltage source to obtain the output coding listed
in Table 3.

TECHNICAL NOTES

1. Rated performance requires using good high-frequency

circuit board layout techniques. Connect the digital and
analog grounds to one point, the analog ground plane
beneath the converter. Due to the inductance and resis-
tance of the power supply return paths, return the analog
and digital ground separately to the power supplies.
SIGNAL GROUND (pin 4) is not internally connected to
ANALOG GROUND (pins 6, 15).

2. Bypass the analog and digital supplies and the +10V REF.

OUT (pin 1) to ground with a 4.7µF, 25V tantalum electro-
lytic capacitor in parallel with a 0.1µF ceramic capacitor.

3. CODING SELECT(pin 8) is compatible with CMOS/TTL

logic levels for those users desiring logic control of this
function. There is an internal pull-up resistor on this pin;
connect to +5V or leave open for logic 1. See the Calibra-
tion Procedure for selecting an output coding.

4. To enable the three-state outputs, connect ENABLE (pin 9)

to a logic "0" (low). To disable, connect pin 9 to a logic "1"
(high).

Figure 2. ADS-942 Timing Diagram

INPUT RANGE

INPUT PIN

TIE TOGETHER

0 +10V

Pin 3

Pins 2 and 4

±5V

Pin 3

Pins 1 and 2

Table 1. Input Connections

CALIBRATION PROCEDURE

1. Connect the converter per Figure 3 and Table 1 for the

appropriate input voltage range. Apply a pulse of 35
nanoseconds minimum to START CONVERT (pin 32) at a
rate of 200kHz. This rate is chosen to reduce flicker if LED's
are used on the outputs for calibration purposes.

2. Zero Adjustments

Apply a precision voltage reference source between
ANALOG INPUT (pin 3) and SIGNAL GROUND (pin 4),
then adjust the reference source output per Table 2.

Note: Scale is approximately 25ns per division.

START

CONVERT

INTERNAL S/H

N+1

35ns max..

EOC

10ns typ.
15ns max.

OUTPUT

DATA

DATA N VALID

300ns min.

Hold

DATA N-1 VALID

30ns max.

35ns min., 50ns typ., 60 ns max

35ns typ.

350ns min.

150ns max.

Aquisition Time

INVALID DATA

200ns max.

Conversion Time

300ns typ., 325ns max.

ADS-942

Removing System Errors

Use external potentiometers to remove system errors or to
reduce the small initial errors to zero. Use a 100

trimpot in

series with the analog input for gain adjustment. Use a fixed
50

resistor instead of the trimpot for operation without

adjustment. Use a 20k

trimpot with the wiper tied to OFFSET

ADJUST (pin 5) for zero/offset adjustment. Connect pin 5 to
ANALOG GROUND (pin 6) for operation without zero/offset
adjustment.

Figure 3. ADS-942 Connection Diagram

ADS-942

20k

BIT 1 OUT (MSB)

BIT 2 OUT

BIT 3 OUT

BIT 4 OUT

BIT 5 OUT

BIT 6 OUT

BIT 7 OUT

BIT 8 OUT

BIT 9 OUT

BIT 10 OUT

BIT 11 OUT

BIT 12 OUT

BIT 13 OUT

BIT 14 OUT (LSB)

OVERFLOW

EOC

ANALOG
GROUND

DIGITAL
GROUND

0.1µF

4.7µF

0.1µF

ENABLE

4.7µF

+10V REF. OUT

CODING SELECT

+5V

15V

+15V

OFFSET
ADJUST

0.1µF

4.7µF

6, 14, 15

0.1µF

4.7µF

15V

+15V

START CONVERT

ANALOG INPUT

100

BIPOLAR

4 SIGNAL GROUND

ZERO/OFFSET

ADJUST

0 to +10V

GAIN ADJUST

+5V

Table 3. Output Coding

UNIPOLAR

INPUT VOLT.

OUTPUT CODING

INPUT VOLT.

BIPOLAR

SCALE

0 TO +10V

MSB

LSB

MSB

LSB

MSB

LSB

±5V

SCALE

+FS 1 LSB

+9.999390

11 1111 1111 1111

00 0000 0000 0000

01 1111 1111 1111

+4.999390

+FS 1LSB

+7/8 FS

+8.750000

11 1000 0000 0000

00 0111 1111 1111

01 1000 0000 0000

+3.750000

+3/4FS

+3/4 FS

+7.500000

11 0000 0000 0000

00 1111 1111 1111

01 0000 0000 0000

+2.500000

+1/2FS

+1/2 FS

+5.000000

10 0000 0000 0000

01 1111 1111 1111

00 0000 0000 0000

0.000000

+1/4 FS

+2.500000

01 0000 0000 0000

10 1111 1111 1111

11 0000 0000 0000

2.500000

1/2FS

+1/8 FS

+1.250000

00 1000 0000 0000

11 0111 1111 1111

10 1000 0000 0000

3.750000

3/4FS

+1 LSB

+0.000610

00 0000 0000 0001

11 1111 1111 1110

10 0000 0000 0001

4.999390

FS+1LSB

0.000000

00 0000 0000 0000

11 1111 1111 1111

10 0000 0000 0000

5.000000

STRAIGHT BIN.

COMP. BINARY

OFF. BINARY

COMP. OFF. BIN.

TWO'S COMP.

ADS-942

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 (T

= +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. 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.

Figure 4. FFT Analysis of ADS-942

100

110

120

130

140

150

Frequency (MHz)

(fs = 2MHz, fin = 490kHz, Vin = 0.5dB, 16,384-point FFT)

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