ADS-945

14-Bit, 10MHz

Sampling A/D Converters

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

Figure 1. ADS-945 Functional Block Diagram

FEATURES

14-bit resolution

10MHz minimum throughput

Functionally complete

No missing codes

Low power, 4.2W

Excellent dynamic performance

Internally clamped input

Edge triggered

TTL compatible

2" x 4" module

Very low profile

GENERAL DESCRIPTION

The low-cost ADS-945 is a high-performance, 14-bit, 10MHz
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-945
has been optimized to achieve a THD of 82dB and a
SNR of 79dB.

Packaged in a 2" x 4" module, the functionally complete
ADS-945 contains a fast-settling sample/hold amplifier, a
subranging (two-pass) A/D converter, a precise voltage
reference, timing/control logic, three-state outputs, and
error-correction circuitry. Digital inputs and outputs are TTL
compatible (except for pins 29 and 30 which are ECL).

Requiring ±15V, +5V and 5.2V supplies, the ADS-945
typically dissipates 4.2W. The unit is offered with a bipolar
input range of ±1.25V. Models are available for use in either
commercial (0 to +70°C) or military (55 to +125°C) operating
temperature ranges. Typical applications include radar signal
analysis, medical/graphic imaging, and FFT spectrum
analysis.

ANALOG GROUND

70-76

ANALOG GROUND

ANALOG INPUT

+5V ANALOG SUPPLY

5-6

ANALOG GROUND

64-68

ANALOG GROUND

+10V REFERENCE OUT

5.2V ANALOG SUPPLY

ANALOG GROUND

GAIN ADJUST

NO CONNECT

10-11

DO NOT CONNECT

58-60

DIGITAL GROUND

15V SUPPLY

5.2V DIGITAL SUPPLY

ANALOG GROUND

DO NOT CONNECT

+15V SUPPLY

+5V DIGITAL SUPPLY

15-17

ANALOG GROUND

DIGITAL GROUND

OFFSET ADJUST

BIT 1 (MSB)

19-25

ANALOG GROUND

BIT 2

MISSING PIN

BIT 3

DIGITAL GROUND

BIT 4

DIGITAL GROUND

BIT 5

T/H STATUS

BIT 6

T/H STATUS

BIT 7

DIGITAL GROUND

BIT 8

START CONVERT

BIT 9

OVERFLOW

BIT 10

OUTPUT ENABLE (OE)

BIT 11

DIGITAL GROUND

BIT 12

O.S. 3 *

BIT 13

DIGITAL GROUND

BIT 14 (LSB)

DIGITAL GROUND

INPUT/OUTPUT CONNECTIONS

PIN

FUNCTION

PIN

FUNCTION

* Refer to Timing Diagram notes

REF

DAC

-
S

I
S

TIMING AND

CONTROL LOGIC

ANALOG INPUT 4

START CONVERT 32

T/H STATUS 29

BUFFER

I
G

I
T

I
O

I
C

FLASH

ADC

FLASH

ADC

AMP

GAIN

CIRCUIT

GAIN ADJUST 9

OFFSET
CIRCUIT

OFFSET ADJUST 18

+15V

SUPPLY

O.S. 3

15V

SUPPLY

+5V DIGITAL

SUPPLY

34 OUTPUT ENABLE

T/H

+10 REF. OUT 7

T/H STATUS 30

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)

33 OVERFLOW

1,2,3,5,6,8,13,15,17,

19-25,62,64-68,70-76

ANALOG GROUND

27,28,31,35,37-39,54,58-60

DIGITAL

GROUND

CONNECT

5.2V DIGITAL

SUPPLY

26 MISSING PIN

10,11,56 DO NOT CONNECT

CASE

DGND

AGND

ADS-945

+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

±1.25

Volts

Input Resistance

300

500

300

550

300

500

Input Capacitance

Input Bias Current

±3

µA

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)

±0.5

±0.75

LSB

Differential Nonlinearity (f

= 10kHz)

±0.5

±0.75

±0.5

±0.75

0.95

±0.75

+1.5

LSB

Full Scale Absolute Accuracy

±0.2

±0.4

±0.3

±0.5

±0.3

±0.7

%FSR

Bipolar Offset Error (Tech Note 2)

±0.15

±0.25

±0.5

±0.3

±0.7

%FSR

Gain Error (Tech Note 2)

±0.1

±0.2

±0.4

±0.3

±0.7

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

100kHz to 2.5MHz

2.5MHz to 5MHz

Signal-to-Noise Ratio

(& distortion, 0.5dB)
dc to 100kHz

1MHz to 2.5MHz

2.5MHz to 5MHz

Noise

110

µVrms

Two-tone Intermodulation

Distortion (f

= 1.975MHz,

2.45MHz, f

= 10MHz, 0.5dB)

Input Bandwidth (3dB)

Small Signal (20dB input)

100

MHz

Large Signal (0.dB input)

MHz

Feedthrough Rejection (f

= 4.85MHz)

Slew Rate

±850

V/µs

Aperture Delay Time

Aperture Uncertainty

ps rms

PARAMETERS

LIMITS

UNITS

+15V Supply (Pins 14)

0 to +17

Volts

15V Supply (Pin 12)

0 to 17

Volts

+5V Supply (Pins 55, 69)

0 to +6

Volts

5V Supply (Pin 57, 63)

0 to 6

Volts

Digital Input (Pin 32, 34)

0.3 to +V

+0.3

Volts

Analog Input (Pin 4)

5 to +5

Volts

Lead Temperature (10 seconds)

+300

°C

PARAMETERS

MIN.

TYP.

MAX.

UNITS

Operating Temp. Range, Case

ADS-945

+70

°C

ADS-945EX

+125

°C

Thermal Impedance

°C/Watt

Storage Temperature Range

+150

°C

Package Type

2" x 4" module

Weight

2.1 oz. (60 grams)

ABSOLUTE MAXIMUM RATINGS

PHYSICAL/ENVIRONMENTAL

FUNCTIONAL SPECIFICATIONS

= +25°C, ±V

= ±15V, +V

= +5V, V

= 5.2V, 10MHz sampling rate, and a minimum 10 minute warmup unless otherwise specified.)

ADS-945

+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, 2.5V step)

Overvoltage Recovery Time

100

A/D Conversion Rate

MHz

ANALOG OUTPUT

Reference Output

+9.99

+10

+10.01

+9.99

+10

+10.01

+9.99

+10

+10.01

Volts

Reference Temperature Drift

±40

ppm/°C

Reference Load Curent

2.0

DIGITAL OUTPUTS

Logic Levels

Logic "1"

+2.7

Volts

Logic "0"

+0.5

Volts

Logic Loading "1"

0.4

Logic Loading "0"

Delay, Falling Edge of T/H

to Output Data Valid

Delay, Edge of ENABLE

to Output Data Valid/Invalid

Output Coding

Complementary Offset Binary

POWER REQUIREMENTS

Power Supply Ranges

+15V Supply

+14.25

+15.0

+15.75

+14.25

+15.0

+15.75

+14.25

+15.0

+15.75

Volts

15V Supply

14.25

15.0

15.75

14.25

15.0

15.75

14.25

15.0

15.75

Volts

+5V Supply

+4.75

+5.0

+5.25

+4.75

+5.0

+5.25

+4.75

+5.0

+5.25

Volts

5.2V Supply

4.95

5.2

5.45

4.95

5.2

5.45

4.95

5.2

5.45

Volts

Power Supply Currents

+15V Supply

+35

+45

+35

+45

+35

+45

15V Supply

+5V Supply

+140

+160

+140

+160

+140

+160

5.2V Supply

430

460

430

460

430

460

Power Dissipation

4.2

4.5

4.2

4.5

4.2

4.5

Watts

Power Supply Rejection

±0.04

%FSR/%V

Footnotes:

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.

The input to the ADS-945 is internally clamped at ±2.3V.

An 50ns wide start convert pulse is used for all production testing. For
applications requiring less than a 10MHz sampling rate, a wider start convert
can be used.

6.02

(SNR + Distortion) 1.76 + 20 log

Full Scale Amplitude

Actual Input Amplitude

Effective bits is equal to:

This is the time required before the A/D output is valid after the analog input is
back within its range.

Typical +5V and 5.2V current drain breakdowns are as follows:

+5V

Analog

= +100mA

5.2V

Analog

= 210mA

+5V

Digital

= +40mA

5.2V

Digital

= 220mA

+5V

Total

= +140mA

5.2V

Total

= 430mA

TECHNICAL NOTES

1. Obtaining fully specified performance from the ADS-945

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 directly to a large analog
ground plane beneath the package.

Bypass all power supplies to ground with 10

F tantalum

capacitors in parallel with 0.1

F ceramic capacitors. The

bypass capacitors should be located as close to the
unit as possible.

2. The ADS-945 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. The typical
adjustment range is ±0.2%FSR for this circuitry.

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. To enable the three-state outputs, apply a logic "0" (low) to

OUTPUT ENABLE (pin 34). To disable, apply a logic "1"
(high) to pin 34.

4. A passive bandpass filter (Allen Avionics F4202 Series) is

used at the input of the A/D for all production testing.

5. The ADS-945's digital outputs should not be directly

connected to a noisy data bus. Drive the bus with 573 or
574 type latches and use "low-noise" logic, such as the
74LS series.

ADS-945

CALIBRATION PROCEDURE

(Refer to Figure 2 and Table 1)

Note: Connect pin 18 to ANALOG GROUND (pin 19) for
operation without zero/offset adjustment. Connect pin 9 to
ANALOG GROUND (pin 8) for operation without gain
adjustment.

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 circuit in Figure 2 are guaranteed to
compensate for the ADS-945'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.

For the ADS-945, offset adjusting 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 (+76.3

V).

Gain adjusting is accomplished when all bits are 0's and the
LSB just changes from a 0 to a 1. This transition ideally
occurs when the analog input is at +full scale minus 1 ½ LSB's
(+1.249771V) .

Note: Due to inherent system noise, the averaging of

several

conversions may be needed to accurately

adjust both offset

and gain to 1LSB of accuracy.

Zero/Offset Adjust Procedure

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

(pin 32) so the converter is continuously converting.

2. Apply +76.3

V to the ANALOG INPUT (pin 4).

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 +1.249771V to the ANALOG INPUT (pin 4).

2. Adjust the gain potentiometer until all output bits are 0's

and the LSB flickers between 0 and 1.

3. To confirm proper operation of the device, vary the applied

input voltage to obtain the output coding listed in Table 1.

Note: A single +5V supply can be used for both the +5V
ANALOG and the +5V DIGITAL. If separate supplies are
used, the difference between the two can not exceed
100mV. This also applies to the 5.2V supply requirements.

Datel recommends using ferrite beads to separate the analog
and digital supplies (FAIR-RITE # 2643000301.)

Figure 2. ADS-945 Connection Diagram

OUTPUT CODING

INPUT RANGE

BIPOLAR

MSB

LSB

±1.25V

SCALE

00 0000 0000 0000

+1.249847

+FS 1 LSB

00 0111 1111 1111

+0.937500

+3/4 FS

00 1111 1111 1111

+0.625000

+1/2FS

01 1111 1111 1111

0.000000

10 1111 1111 1111

0.625000

1/2FS

11 0111 1111 1111

0.937500

3/4FS

11 1111 1111 1110

1.249847

FS +1 LSB

11 1111 1111 1111

1.250000

COMP. OFF. BINARY

Table 1. Output Coding

ADS-945

20k

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)

OUTPUT ENABLE

OVERFLOW

T/H STATUS

ANALOG INPUT

ANALOG
SUPPLY

DIGITAL
SUPPLY

54
58-60

OFFSET
ADJUST

0.1µF

10µF

64-68

0.1µF

10µF

5.2V

+5V

START CONVERT

+10 REF. OUT

0.1µF

10µF

0.1µF

10µF

5.2V

+5V

0.1µF

10µF

13
15-17

0.1µF

10µF

15V

+15V

DIGITAL
SUPPLY

ANALOG
SUPPLY

0.1µF

GAIN

ADJUST

20k

DIGITAL
GROUND

ANALOG
GROUND

15V

+15V

15V

ADS-945

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BIT 4

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BIT 2

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