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

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

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

BIT 1 (MSB)

ANALOG GROUND

BIT 2

OFFSET ADJUST

BIT 3

+5V ANALOG SUPPLY

BIT 4

ANALOG INPUT

BIT 5

5V SUPPLY

BIT 6

ANALOG GROUND

BIT 7

START CONVERT

BIT 8

EOC

BIT 9

BIT 14 (LSB)

BIT 10

BIT 13

BIT 11

DIGITAL GROUND

BIT 12

+5V DIGITAL SUPPLY

ADS-946

14-Bit, 8MHz

Sampling A/D Converters

REF

DAC

I
S

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

I
G

I
T

I
O

I
C

FLASH

ADC

FLASH

ADC

POWER AND GROUNDING

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

PARAMETERS

MIN.

TYP.

MAX.

UNITS

Operating Temp. Range, Case

ADS-946MC, GC

+70

°C

ADS-946MM, GM, 883, G/883

+125

°C

Thermal Impedance

°C/Watt

Storage Temperature Range

+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 +V

+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

Volts

Input Resistance

200

Input Capacitance

DIGITAL INPUT

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

STATIC PERFORMANCE

Resolution

Bits

Integral Nonlinearity (f

= 10kHz)

±0.75

±1

LSB

Differential Nonlinearity (f

= 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

±0.8

%FSR

Bipolar Zero Error (Tech Note 2)

±0.2

±0.4

±0.2

±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 (f

= 10kHz)

Bits

DYNAMIC PERFORMANCE

Peak Harmonics (0.5dB)

dc to 500kHz

500kHz to 1MHz

1MHz to 4MHz

Total Harmonic Distortion (0.5dB)

dc to 500kHz

500kHz to 1MHz

1MHz to 4MHz

Signal-to-Noise Ratio

(w/o distortion, 0.5dB)
dc to 500kHz

500kHz to 1MHz

1MHz to 4MHz

Signal-to-Noise Ratio

(& distortion, 0.5dB)
dc to 500kHz

500kHz to 1MHz

1MHz to 4MHz

Noise

150

µVrms

Two-Tone Intermodulation

Distortion (f

= 2.45MHz,

1.975MHz, f

= 8MHz, 0.5dB)

Input Bandwidth (3dB)

Small Signal (20dB input)

MHz

Large Signal (0.5dB input)

MHz

Feedthrough Rejection (f

= 4MHz)

Slew Rate

±400

V/µs

Aperture Delay Time

Aperture Uncertainty

ps rms

FUNCTIONAL SPECIFICATIONS

= +25°C, ±V

= ±5V, 8MHz sampling rate, and a minimum 3 minute warmup unless otherwise specified.)

ADS-946

+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)

Overvoltage Recovery Time

100

125

100

125

100

125

A/D Conversion Rate

MHz

DIGITAL OUTPUTS

Logic Levels

Logic "1"

+2.4

Volts

Logic "0"

+0.4

Volts

Logic Loading "1"

Logic Loading "0"

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

5V Supply

150

170

150

170

150

170

Power Dissipation

2.2

Watts

Power Supply Rejection

±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 ±V

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

SIGNAL

INPUT

GAIN

ADJUST

1.98k

+5V

ADS-946

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

0.00000

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

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

0.1µF

4.7µF

22, 13

ADS-946

20k

0.1µF

4.7µF

+5V

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

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
(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.

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

N+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.

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