PIN

FUNCTION

PIN

FUNCTION

+3.2V REF. OUT

NO CONNECTION

UNIPOLAR

NO CONNECTION

ANALOG INPUT

+5V ANALOG SUPPLY

ANALOG GROUND

5V SUPPLY

OFFSET ADJUST

ANALOG GROUND

GAIN ADJUST

COMP. BITS

DIGITAL GROUND

OUTPUT ENABLE

FIFO/DIR

OVERFLOW

FIFO READ

EOC

FSTAT1

+5V DIGITAL SUPPLY

FSTAT2

DIGITAL GROUND

START CONVERT

BIT 1 (MSB)

BIT 16 (LSB)

BIT 1 (MSB)

BIT 15

BIT 2

BIT 14

BIT 3

BIT 13

BIT 4

BIT 12

BIT 5

BIT 11

BIT 6

BIT 10

BIT 7

BIT 9

BIT 8

FEATURES

16-bit resolution

1MHz sampling rate

Functionally complete

No missing codes over full military temperature range

Edge-triggered

±5V supplies, 1.85 Watts

Small, 40-pin, ceramic TDIP

87dB SNR, 89dB THD

Ideal for both time and frequency-domain applications

16-Bit, 1MHz

Sampling A/D Converters

I N N O V A T I O N a n d E X C E L L E N C E

GENERAL DESCRIPTION

The low-cost ADS-931 is a 16-bit, 1MHz sampling A/D
converter. This device accurately samples full-scale input
signals up to Nyquist frequencies with no missing codes. The
dynamic performance of the ADS-931 has been optimized to
achieve a signal-to-noise ratio (SNR) of 87dB and a total
harmonic distortion (THD) of 89dB.

Packaged in a 40-pin TDIP, the functionally complete ADS-931
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-931 only requires the rising edge of the start
convert pulse to operate.

Requiring only ±5V supplies, the ADS-931 dissipates 1.85
Watts. The device is offered with a bipolar (±2.75V) analog
input range or a unipolar (0 to 5.5V) input range. Models are
available for use in either commercial (0 to +70°C) or military
(55 to +125°C) operating temperature ranges. A proprietary,
auto-calibrating, error-correcting circuit enables the device to
achieve specified performance over the full military
temperature range. Typical applications include medical
imaging, radar, sonar, communications and instrumentation.

INPUT/OUTPUT CONNECTIONS

ADS-931

DATEL, Inc., Mansfield, MA 02048 (USA)

Tel: (508)339-3000, (800)233-2756 Fax: (508)339-6356

E-mail:sales@datel.com

Internet: www.datel.com

Figure 1. ADS-931 Functional Block Diagram

-
S

I
S

29 BIT 1 (MSB)

28 BIT 1 (MSB)

27 BIT 2

26 BIT 3

25 BIT 4

24 BIT 5

23 BIT 6

22 BIT 7

21 BIT 8

20 BIT 9

19 BIT 10

18 BIT 11

17 BIT 12

16 BIT 13

15 BIT 14

14 BIT 15

13 BIT 16 (LSB)

TIMING AND

CONTROL LOGIC

GAIN ADJUST 6

+3.2V REF. OUT 1

OFFSET ADJUST 5

EOC 32

ANALOG GROUND 4, 36

DIGITAL GROUND 7, 30

+5V DIGITAL SUPPLY 31

5V SUPPLY 37

+5V ANALOG SUPPLY 38

NO CONNECTION 39, 40

POWER and GROUNDING

-
P

-
T

-
D

I
G

I
T

S/H

GAIN

ADJUST

CKT.

OFFSET
ADJUST

CKT.

PRECISION

+3.2V REFERENCE

ANALOG INPUT 3

START CONVERT 12

COMP. BITS 35

10 FSTAT1

11 FSTAT2

8 FIFO/DIR

9 FIFO/READ

34 OUTPUT ENABLE

33 OVERFLOW

UNIPOLAR 2

OFFSET ADJUST 5

ADS-931

+25°C

0 to +70°C

55 to +125°C

ANALOG INPUTS

MIN.

TYP.

MAX.

MIN.

TYP.

MAX.

MIN.

TYP.

MAX.

UNITS

Input Voltage Ranges

Unipolar

0 to 5.5

Volts

Bipolar

±2.75

Volts

Input Resistance (pin 3)

685

Input Resistance (pin 2)

400

426

Input Capacitance

DIGITAL INPUTS

Logic Levels

Logic "1"

+2.0

Volts

Logic "0"

+0.8

Volts

Logic Loading "1"

+20

µA

Logic Loading "0"

µA

Start Convert Positive Pulse Width

100

STATIC PERFORMANCE

Resolution

Bits

Integral Nonlinearity

±1

±1.5

±2

LSB

Differential Nonlinearity (f

= 10kHz)

0.95

±0.5

+1.0

0.95

±0.5

+1.0

0.95

±0.5

+1.5

LSB

Full Scale Absolute Accuracy

±0.1

±0.3

±0.15

±0.5

±0.8

%FSR

Bipolar Zero Error (Tech Note 2)

±0.1

±0.2

±0.4

±0.5

±0.9

%FSR

Bipolar Offset Error (Tech Note 2)

±0.1

±0.3

±0.2

±0.5

±0.4

±0.9

%FSR

Gain Error (Tech Note 2)

±0.1

±0.3

±0.15

±0.5

±0.9

No Missing Codes (f

= 10kHz)

Bits

DYNAMIC PERFORMANCE

Peak Harmonics (0.5dB)

dc to 250kHz

250kHz to 500kHz

Total Harmonic Distortion (0.5dB)

dc to 250kHz

250kHz to 500kHz

Signal-to-Noise Ratio

(w/o distortion, 0.5dB)
dc to 250kHz

250kHz to 500kHz

Signal-to-Noise Ratio

(& distortion, 0.5dB)
dc to 250kHz

250kHz to 500MHz

Noise

µVrms

Two-Tone Intermodulation

Distortion (f

= 98kHz,

240kHz, f

= 1MHz, 0.5dB)

Input Bandwidth (3dB)

Small Signal (20dB input)

4.8

MHz

Large Signal (0.5dB input)

4.1

MHz

Feedthrough Rejection

= 480kHz)

Slew Rate

±51

V/µs

Aperture Delay Time

Aperture Uncertainty

ps rms

S/H Acquisition Time

( to ±0.001%FSR, 5.5V step)

700

725

700

725

700

725

PARAMETERS

MIN.

TYP.

MAX.

UNITS

Operating Temp. Range, Case

ADS-931MC

+70

°C

ADS-931MM

+125

°C

Thermal Impedance

°C/Watt

Storage Temperature Range

+150

°C

Package Type

40-pin, metal-sealed, ceramic TDIP

Weight

0.56 ounces (16 grams)

ABSOLUTE MAXIMUM RATINGS

PARAMETERS

LIMITS

UNITS

+5V Supply (Pins 31, 38)

0 to +6

Volts

5V Supply (Pin 37)

0 to 6

Volts

Digital Inputs (Pins 8, 9, 12, 34, 35)

0.3 to +V

+0.3

Volts

Analog Input (Pin 3)

Volts

Bipolar

±5

Volts

Unipolar

10 to +5

Volts

Lead Temperature (10 seconds)

+300

°C

PHYSICAL/ENVIRONMENTAL

FUNCTIONAL SPECIFICATIONS

= +25°C, ±V

= ±5V, +V

= +5V, 1MHz sampling rate, and a minimum 3 minute warm-up unless otherwise specified.)

ADS-931

+25°C

0 TO +70°C

55 TO +125°C

DYNAMIC PERFORMANCE

(Cont.)

MIN.

TYP.

MAX.

MIN.

TYP.

MAX.

MIN.

TYP.

MAX.

UNITS

Overvoltage Recovery Time

1000

A/D Conversion Rate

MHz

Footnotes:

Effective bits is equal to:

All power supplies must be on before applying a start convert pulse. All supplies
and the clock (START CONVERT) must be present during warm-up periods.
The device must be continuously converting during this time. There is a slight
degradation in performance when operating the device in the unipolar mode.

When COMP. BITS (pin 35) is low, logic loading "0" will be 350µA.

A 1MHz clock with a positive pulse width is used for all production testing. See
Timing Diagram for more details.

40ns < Start Pulse < 175ns or 280ns < Start Pulse < 460ns

6.02

(SNR + Distortion) 1.76 + 20 log

Full Scale Amplitude

Actual Input Amplitude

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 ±4.75V (bipolar) or +2 to 7.5V (unipolar).

The minimum supply voltages of +4.9V and 4.9V for ±V

are required for

55°C operation only. The minimum limits are +4.75V and 4.75V when
operating at +125°C.

TECHNICAL NOTES

1. Obtaining fully specified performance from the ADS-931

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 perfor-
mance, tie all ground pins (4, 7, 30 and 36) directly to a large
analog ground plane beneath the package.

Bypass all power supplies and the +3.2V reference output 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-931 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 Figure 2. When using this
circuitry, or any similar offset and gain calibration hardware,
make adjustments following warm-up. To avoid interaction,
always adjust offset before gain. Tie pins 5 and 6 to
ANALOG GROUND (pin 4) if not using offset and gain
adjust circuits.

3. Pin 35 (COMP. BITS) is used to select the digital output

coding format of the ADS-931 (see Tables 2a and 2b). When
this pin has a TTL logic "0" applied, it complements the ADS-
931's B1-B16 & B1 outputs.

Pin 35 is TTL compatible and can be directly driven with digital
logic in applications requiring dynamic control over its function.
There is an internal pull-up resistor on pin 35 allowing it to be
either connected to +5V or left open when a logic "1" is
required.

4. To enable the three-state outputs, connect OUTPUT

ENABLE (pin 34) to a logic "0" (low). To disable, connect
pin 34 to a logic "1" (high).

5. Applying a start convert pulse while a conversion is in

progress (EOC = logic "1") will initiate a new and probably
inaccurate conversion cycle. Data from both the interrupted
and subsequent conversions will be invalid.

ANALOG OUTPUT

Internal Reference

Voltage

3.15

+3.2

3.25

3.15

+3.2

3.25

3.15

+3.2

3.25

Volts

Drift

±30

ppm/°C

External Current

DIGITAL OUTPUTS

Logic Levels

Logic "1"

+2.4

Volts

Logic "0"

+0.4

Volts

Logic Loading "1"

Logic Loading "0"

Delay, Falling Edge of Enable to
Output Data Valid

Output Coding

Straight Binary, Complementary Binary, Complementary Offset Binary,
Complementary Two's Complement, Offset Binary, Two's Complement

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

+225

260

+225

260

+225

260

5V Supply

140

135

140

135

140

135

Power Dissipation

1.85

2.0

1.85

2.0

1.85

2.0

Watts

Power Supply Rejection

±0.07

%FSR/%V

ADS-931

DELAY

PIN

TRANSITION

MIN.

TYP.

MAX.

UNITS

Direct mode to FIFO enabled

FIFO enabled to direct mode

FIFO READ to output data valid

FIFO READ to status update when changing
from <half full (1 word) to empty

FIFO READ to status update when changing
from

half full (8 words) to <half full (7 words)

110

FIFO READ to status update when changing
from full (16 words) to

half full (15 words)

190

Falling edge of EOC to status update when writing
first word into empty FIFO

190

Falling edge of EOC to status update when
changing FIFO from <half full (7 words) to

110

half full (8 words)

Falling edge of EOC to status update when filling
FIFO with 16th word

When the FIFO is initially empty, digital data from the first
conversion (the "oldest" data) appears at the output of the
FIFO immediately after the first conversion has been
completed and remains there until the FIFO is read.

If the output three-state register has been enabled (logic "0"
applied to pin 34), data from the first conversion will appear at
the output of the ADS-931. Attempting to write a 17th word to a
full FIFO will result in that data, and any subsequent conversion
data, being lost.

Once the FIFO is full (indicated by FSTAT1 and FSTAT2 both
equal to "1"), it can be read by dropping the FIFO READ line
(pin 9) to a logic "0" and then applying a series of 15 rising
edges to the read line. Since the first data word is already
present at the FIFO output, the first read command (the first
rising edge applied to FIFO READ) will bring data from the
second conversion to the output. Each subsequent read
command/rising edge brings the next word to the output lines.
After the 15th rising edge brings the 16th data word to the
FIFO output, the subsequent falling edge on READ will update
the status outputs (after a 20ns maximum delay) to FSTAT1 =
0, FSTAT2 = 1 indicating that the FIFO is empty.

If a read command is issued after the FIFO empties, the last
word (the 16th conversion) will remain present at the outputs.

FIFO Reset Feature

At any time, the FIFO can be reset to an empty state by putting
the ADS-931 into its "direct" mode (logic "0" applied to pin 8,
FIFO/DIR) and also applying a logic "0" to the FIFO READ line
(pin 9). The empty status of the FIFO will be indicated by
FSTAT1 going to a "0" and FSTAT2 going to a "1". The status
outputs change 40ns after applying the control signals.

FIFO Status, FSTAT1 and FSTAT2

Monitor the status of the data in the FIFO by reading the two
status pins, FSTAT1 (pin 10) and FSTAT2 (pin 11).

CONTENTS

FSTAT1

FSTAT2

Empty (0 words)

<half full (<8 words)

half-full or more (

8 words)

Full (16 words)

Table 1. FIFO Delays

6. Do not enable/disable or complement the output bits or read

from the FIFO during the conversion process (from the rising
edge of EOC to the falling edge of EOC).

7. The OVERFLOW bit (pin 33) switches from 0 to 1 when the

input voltage exceeds that which produces an output of all
1's or when the input equals or exceeds the voltage that
produces all 0's. When COMP BITS is activated, the above
conditions are reversed.

8. When configuring the ADS-931 for the unipolar mode, Pin 1

(+3.2V REF.) should be connected to Pin 2 (Unipolar) through
a non-inverting op-amp. For precision DC applications an OP-
07 type amplifier is recommended, while AC applications
requiring the lowest level of harmonic distortion should
consider the AD9631.
When configuring the ADS-931 for the bipolar mode, Pin 2
(Unipolar) should be physically disconnected from the
surrounding circuitry. This will help prevent noise from
coupling into the A/D.

INTERNAL FIFO OPERATION

The ADS-931 contains an internal, user-initiated, 18-bit, 16-word
FIFO memory. Each word in the FIFO contains the 16 data bits
as well as the MSB and overflow bits. Pins 8 (FIFO/DIR) and 9
(FIFO READ) control the FIFO's operation. The FIFO's status
can be monitored by reading pins 10 (FSTAT1) and 11 (FSTAT2).

When pin 8 (FIFO/DIR) has a logic "1" applied, the FIFO is
inserted into the digital data path. When pin 8 has a logic "0"
applied, the FIFO is transparent and the output data goes
directly to the output three-state register (whose operation is
controlled by pin 34 (ENABLE)). Read and write commands
to the FIFO are ignored when the ADS-931 is operated in the
"direct" mode. It takes a maximum of 20ns to switch the FIFO
in or out of the ADS-931's digital data path.

FIFO Write and Read Modes

Once the FIFO has been enabled (pin 8 high), digital data is
automatically written to it, regardless of the status of FIFO
READ (pin 9). Assuming the FIFO is initially empty, it will
accept data (18-bit words) from the next 16 consecutive A/D
conversions. As a precaution, pin 9 (which controls the
FIFO's READ function) should not be low when data is first
written to an empty FIFO.

ADS-931

for operation without gain adjustment.

Zero/Offset Adjust Procedure

1. Apply a train of pulses to the START CONVERT input (pin

12) so that the converter is continuously converting.

2. For unipolar or bipolar zero/offset adjust, apply 42µV to the

ANALOG INPUT (pin 3).

3. For bipolar inputs, adjust the offset potentiometer until the

code flickers between 1000 0000 0000 0000 and 0111
1111 1111 1111 with pin 35 tied high (complementary
offset binary) or between 0111 1111 1111 1111 and 1000
0000 0000 0000 with pin 35 tied low (offset binary).
For unipolar inputs, adjust the offset potentiometers until all
output bits are 0's and the LSB flickers between 0 and 1
with Pin 35 tied high (straight binary) or until all bits are 1's
and the LSB flickers between 0 and 1 with pin 35 tied low
(complementary binary).

4. Two's complement coding requires using BIT 1 (MSB) (pin

29). With pin 35 tied low, adjust the trimpot until the output
code flickers between all 0's and all 1's.

Gain Adjust Procedure

1. Apply +2.749874V to the ANALOG INPUT (pin 3).

2. For bipolar inputs, adjust the gain potentiometer until all output

bits are 0's and the LSB flickers between a 1 and 0 with pin 35
tied high (complementary offset binary) or until all output bits
are 1's and the LSB flickers between a 1 and 0 with pin 35 tied
low (offset binary).

3. Two's complement coding requires using BIT 1 (MSB)

(pin 29). With pin 35 tied low, adjust the gain trimpot until
the output code flickers equally between 0111 1111 1111
1111 and 0111 1111 1111 1110.

CALIBRATION PROCEDURE

Connect the converter per Figure 2. Any offset/gain calibration
procedures should not be implemented until the device is fully
warmed up. To avoid interaction, adjust offset before gain. The
ranges of adjustment for the circuits in Figure 2 are guaranteed
to compensate for the ADS-931'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 is accomplished by connecting LED's to the
digital outputs and performing adjustments 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.

For the ADS-931, offset adjusting is normally accomplished
when the analog input is 0 minus ½ LSB (42µV). See Table
2b for the proper bipolar output coding.

Gain adjusting is accomplished when the analog input is at
nominal full scale minus 1½ LSB's (+2.749874V).

Note: Connect pin 5 to ANALOG GROUND (pin 4) for
operation without zero/offset adjustment. Connect pin 6 to pin 4

Figure 2. Bipolar Connection Diagram

Complementary Offset Binary

Offset Binary

Complementary Two's Complement

(Using MSB, pin 29)

Two's Complement

(Using MSB, pin 29)

Straight Binary

Complimentary Binary

OUTPUT FORMAT

PIN 35 LOGIC LEVEL

Table 2a. Setting Output Coding Selection (Pin 35)

ADS-931

20k

OVERFLOW

EOC

BIT 1 (MSB)

BIT2

BIT 3

BIT 4

BIT 5

BIT 6

BIT 7

BIT 8

BIT 9

BIT 10

BIT 11

BIT 12

BIT 13

BIT 14

BIT 15

BIT 16 (LSB)

ANALOG
GROUND

DIGITAL
GROUND

0.1µF

4.7µF

0.1µF

COMP. BITS

4.7µF

+3.2V
REF. OUT

FIFO READ

7, 30

+5V
DIGITAL

+5V

OFFSET
ADJUST

GAIN

ADJUST

0.1µF

4.7µF

4, 36

0.1µF

4.7µF

20k

+5V

+5V ANALOG

START CONVERT

ANALOG INPUT

ENABLE

FIFO/DIR

FSTAT1

FSTAT2

+5V

UNIPOLAR

CONNECT for UNIPOLAR MODE

6.8µF

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