Figure 1. ADS-949 Functional Block Diagram

FEATURES

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14-bit resolution

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·

12.8MHz minimum sampling rate

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No missing codes over full military temperature range

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Ideal for both time and frequency-domain applications

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Excellent THD (81dB) and SNR (78dB)

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Edge-triggered

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Small, 32-pin, ceramic DDIP or SMT

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Low-power, 2 Watts

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Low cost

GENERAL DESCRIPTION

The low-cost ADS-949 is a 14-bit, 12.8MHz 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-949 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-949 contains a fast-settling
sample/hold amplifier, a subranging A/D converter, an internal
reference, timing/control logic, and error-correction circuitry.
Digital input and output levels are TTL. The ADS-949 only
requires the rising edge of a start convert pulse to operate.

Requiring only +15V, +5V and 5V supplies, the ADS-949
typically dissipates just 2 Watts. The device is offered with a
Bipolar input range of ±2.5V and Unipolar range of 0 to 5 volts.
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 allows
the device to achieve specified performance over the full
military temperature range.

INPUT/OUTPUT CONNECTIONS

PIN

FUNCTION

PIN

FUNCTION

VIN A

RANGE

VIN B

GAIN ADJUST

+5V ANALOG

OFFSET ADJ.

ANALOG GND

RANGE REF.

+15V

2.5V REF.

+5V DIGITAL

START CONVERT

DIGITAL GND

EOC

OVERFLOW

ENABLE

MSB

BIT 14 (LSB)

BIT 1 (MSB)

BIT 13

BIT 2

BIT 12

BIT 3

BIT 11

BIT 4

BIT 10

BIT 5

BIT 9

BIT 6

BIT 8

BIT 7

ADS-949

14-Bit, 12.8MHz

Sampling A/D Converters

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

Tel: (508)339-3000, (800)233-2765 Fax: (508)339-6356

E-mail: sales@datel.com

Internet: www.datel.com

REF

DAC

REGI

STE

REGI

STE

OUTP

UT REGI

STE

10 BIT 14 (LSB)

11 BIT 13

12 BIT 12

13 BIT 11

14 BIT 10

15 BIT

16 BIT

17 BIT 7

18 BIT 6

19 BIT 5

20 BIT

21 BIT

22 BIT

23 BIT

(MSB)

24 MSB

TIMING AND

CONTROL LOGIC

OFFSET ADJUST 4

VIN A

START CONVERT 7

EOC 8

GAIN ADJUST

+5V ANALOG SUPPLY 30

+5V DIGITAL SUPPLY 27

V RANGE

5.2V SUPPLY

+15V SUPPLY

ANALOG GROUND

DIGITAL GROUND

S/H

BUFFER

CORRE

CTI

N L

OGI

FLASH

ADC

FLASH

ADC

POWER AND GROUNDING

AMP

9 ENABLE

25 OVERFLOW

VIN B

2.5 V REF 6

ADS-949

+25°C

0 to +70°C

55 to +125°C

ANALOG INPUT

MIN.

TYP.

MAX.

MIN.

TYP.

MAX.

MIN.

TYP.

MAX.

UNITS

Bipolar Input Voltage Range

±1

±2.5

±1

±2.5

±1

±2.5

Volts

Unipolar Input Voltage Range

0 to 2

0 to 5

0 to 2

0 to 5

0 to 2

0 to 5

Volts

Input Resistance (Vin A)

400

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

±0.75

±1

LSB

Differential Nonlinearity (f

= 10kHz)

0.95

±0.5

+1.25

0.95

±0.5

+1.25

0.95

±0.5

+1.5

LSB

Full Scale Absolute Accuracy

±0.15

±0.4

±0.15

±0.4

±0.8

%FSR

Bipolar Zero Error (Tech Note 2)

±0.1

±0.3

±0.1

±0.3

±0.6

%FSR

Gain Error (Tech Note 2)

±0.2

±0.4

±0.2

±0.4

±1.5

No Missing Codes (f

= 10kHz)

Bits

DYNAMIC PERFORMANCE

Peak Harmonics (0.5dB)

dc to 1MHz

1MHz to 2.5MHz

2.5MHz to 5MHz

Total Harmonic Distortion (0.5dB)

dc to 1MHz

1MHz to 2.5MHz

2.5MHz to 5MHz

Signal-to-Noise Ratio

(w/o distortion, 0.5dB)
dc to 1MHz

1MHz to 2.5MHz

2.5MHz to 5MHz

Signal-to-Noise Ratio

(& distortion, 0.5dB)
dc to 1MHz

1MHz to 2.5MHz

2.5MHz to 5MHz

Noise

150

µVrms

Two-tone Intermodulation

Distortion (f

= 2.45MHz,

1.975MHz, f

= 10MHz, 0.5dB)

Input Bandwidth (3dB)

Small Signal (20dB input)

MHz

Large Signal (0.5dB input)

MHz

Feedthrough Rejection (f

= 5MHz)

Slew Rate

±400

V/µs

Aperture Delay Time

Aperture Uncertainty

ps rms

FUNCTIONAL SPECIFICATIONS

= +25°C, +V

= +5V, V

= 5V, +Vcc = +15V, 12.8MHz sampling rate, ±2.5V input range, and a minimum 3 minute warmup

unless otherwise specified.)

PARAMETERS

MIN.

TYP.

MAX.

UNITS

Operating Temp. Range, Case

ADS-949MC, GC

+70

°C

ADS-949MM, GM,

+125

°C

Thermal Impedance

°C/Watt

Storage Temperature Range

+150

°C

Package Type

32-pin, metal-sealed, ceramic DDIP or SMT

Weight

0.46 ounces (13 grams)

ABSOLUTE MAXIMUM RATINGS

PARAMETERS

LIMITS

UNITS

+5V Supply (Pins 27, 30)

0 to +6

Volts

+15V Supply (Pin 28)

0 to +16

Volts

5V Supply (Pin 3)

0 to 5.5V

Volts

Digital Input (Pin 7)

0.3 to +V

+0.3

Volts

Analog Input (Pins 1, 2)

±5

Volts

Lead Temperature (10 seconds)

+300

°C

PHYSICAL/ENVIRONMENTAL

ADS-949

+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, 5V step)

Overvoltage Recovery Time

100

A/D Conversion Rate

12.8

MHz

DIGITAL OUTPUTS

Logic Levels

Logic "1"

+2.4

Volts

Logic "0"

+0.4

Volts

Logic Loading "1"

Logic Loading "0"

Output Coding

Straight Binary, 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

5.2V Supply

4.75

5.2

5.45

4.75

5.2

5.45

4.9

5.2

5.45

Volts

+15V Supply

+14.5

+15

+15.5

+14.5

+15

+15.5

+14.5

+15

+15.5

Volts

Power Supply Currents

+5V Supply

+250

+260

+250

+260

+250

+260

5.2V Supply

200

210

200

210

200

210

+15V Supply

+14.5

+15

+15.5

+14.5

+15

+15.5

+14.5

+15

+15.5

Volts

Power Dissipation

2.0

2.25

2.0

2.25

2.0

2.25

Watts

Power Supply Rejection

±0.1

%FSR/%V

Footnotes:

TECHNICAL NOTES

1. Obtaining fully specified performance from the ADS-949

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 (26 and 29) 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-949 achieves its specified accuracies without the

need for external calibration. It is recommended that the

+5VA and +5VD supplies should be powered up from the
same source. If required, the device's small initial offset and
gain errors can be reduced to zero using the adjustment
circuitry shown in Figure 2,3.

When using this circuitry, or any similar offset and gain
calibration hardware, make adjustments following warmup.
To avoid interaction, always adjust offset before gain.

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.

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.

A 50ns wide start convert pulse is used for all production testing. For
applications requiring less than an 12.8MHz sampling rate, wider start convert
pulses can be used.

Effective bits is equal to:

(SNR + Distortion) 1.76 + 20 log

Full Scale Amplitude

Actual Input Amplitude

6.02

ADS-949

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-949'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-949 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 (+153µV).

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
(+2.49954V).

Zero/Offset Adjust Procedure

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

7) so the converter is continuously converting.

2. Apply +153µV to the ANALOG INPUT (pin 1).

3. Adjust the offset potentiometer until the output bits are

10 0000 0000 0000 and the LSB flickers between 0 and 1.

Gain Adjust Procedure

1. Apply +2.49954V to the ANALOG INPUT (pin 1).

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.

INPUT VOLTAGE

ZERO ADJUST

GAIN ADJUST

RANGE

+½ LSB

+FS 1½ LSB

±2.5V

+153µV

+2.49954V

Table 1. Gain and Zero Adjust

Figure 2. Typical ADS-949 Bipolar Connection Diagram

0.1µF

4.7µF

+5VD

AGND

ADS-949

20k

4.7µF

+5VA

DGND

+5V

1VIN A

4 OFFSET ADJUST

7 START CONVERT

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

BIPOLAR

ANALOG

INPUT

START

CONVERT

Bypass Pins 5, 6, 32, with a 4.7µF to Analog Ground.

Note: The Voltage Value at Pin 32 (Range) sets the input voltage range of the ADS-949

eg: If Pin 6 (2.5V Reference Out) is tied to the Range Pin 32 (20k Pot is shorted), then

the input range of the ADS-949 becomes ±2.5V

If the 20k Pot is set at midrange then the input range of the ADS-949 becomes ±1.25V

ZERO/

OFFSET

ADJUST

+5V

31 GAIN ADJUST

GAIN

ADJUST

20K

2 VIN B

9 ENABLE

20k

6 2.5V REF

32 RANGE

+15V

+5VD

4.7µF

+5VA

0.1µF

4.7µF

0.1µF

5 RANGE REF

ADS-949

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 AN8, "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 3. Typical ADS-949 Unipolar Connection Diagram

0.1µF

4.7µF

+5VD

AGND

ADS-949

20k

4.7µF

+5VA

DGND

+5V

1VIN A

4 OFFSET ADJUST

7 START CONVERT

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

UNIPOLAR

ANALOG

INPUT

START

CONVERT

Bypass Pins 5, 6, 32 with a 4.7µF to Analog Ground.

Note: The Voltage Value at Pin 32 (Range) sets the input voltage range of the ADS-949

eg: If Pin 6 (2.5V Reference Out) is tied to the Range Pin 32 (20k Pot is shorted), then

the input range of the ADS-949 becomes 0 to 5V

If the 20k Pot is set at midrange then the input range of the ADS-949 becomes 0 to 2.5V

ZERO/

OFFSET

ADJUST

+5V

31 GAIN ADJUST

GAIN

ADJUST

20K

2 VIN B

9 ENABLE

20k

6 2.5V REF

32 RANGE

+15V

+5VD

4.7µF

+5VA

0.1µF

4.7µF

0.1µF

RANGE REF

Table 3. Output Coding

UNIPOLAR

INPUT VOLT.

OUTPUT CODING

INPUT VOLT.

BIPOLAR

SCALE

0 TO +5V

MSB

LSB

MSB

LSB

±2.5V

SCALE

+FS 1 LSB

+4.999695

11 1111 1111 1111

01 1111 1111 1111

+2.499695

+FS 1LSB

+7/8 FS

+4.375000

11 1000 0000 0000

01 1000 0000 0000

+1.875000

+3/4FS

+3/4 FS

+3.75000

11 0000 0000 0000

01 0000 0000 0000

+1.250000

+1/2FS

+1/2 FS

+2.500000

10 0000 0000 0000

00 0000 0000 0000

0.000000

+1/4 FS

+1.250000

01 0000 0000 0000

11 0000 0000 0000

1.250000

1/2FS

+1/8 FS

+0.625000

00 1000 0000 0000

10 1000 0000 0000

1.875000

3/4FS

+1 LSB

+0.000305

00 0000 0000 0001

10 0000 0000 0001

2.499695

FS+1LSB

0.000000

00 0000 0000 0000

10 0000 0000 0000

2.500000

STRAIGHT BIN.

OFF. BINARY

TWO'S COMP.

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