ADS-943

14-Bit, 3MHz, Low-Distortion

Sampling A/D Converters

edge-triggered, requiring only the rising edge of a start convert
pulse to initiate a conversion.

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 temperature ranges. A
proprietary, auto-calibrating, error-correcting circuit allows the
device to achieve specified performance over the full military
temperature range.

Figure 1. ADS-943 Functional Block Diagram

INPUT/OUTPUT CONNECTIONS

PIN

FUNCTION

PIN

FUNCTION

BIT1 (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

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

FEATURES

14-bit resolution

3MHz minimum sampling rate

Ideal for both frequency and time-domain applications

Excellent peak harmonics, 83dB

Excellent signal-to-noise ratio, 79dB

No missing codes over full military temperature range

±5V supplies, 1.7 Watts

Small, 24-pin ceramic DDIP or SMT

Low cost

GENERAL DESCRIPTION

The low-cost ADS-943 is a 14-bit, 3MHz sampling A/D
converter optimized to meet the demanding dynamic-range
and sampling-rate requirements of contemporary digital
telecommunications applications. The ADS-943's outstanding
dynamic performance is evidenced by a peak harmonic
specification of 83dB and a signal-to-noise ratio (SNR) of
79dB. Additionally, the ADS-943 easily achieves the 2.2MHz
minimum sampling rate required by digital receivers in certain
ADSL, HDSL and ATM applications. The ADS-943 also
addresses size and power constraints normally associated with
these types of applications. This device requires just ±5V
supplies, dissipates 1.7 Watts, and is packaged in a very small
24-pin DDIP.

Although optimized for frequency-domain applications, the
ADS-943's DNL and noise specifications are also outstanding,
thereby making it an equally impressive device for time-domain
applications (graphic and medical imaging, process control,
etc.). In fact, the ADS-943 guarantees no missing codes to the
14-bit level over the full military operating temperature range.

The functionally complete ADS-943 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 unit is

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

DIGITAL GROUND 14

5V SUPPLY 20

ANALOG GROUND 19, 24

S/H

BUFFER

I
G

I
T

I
O

I
C

FLASH

ADC

FLASH

ADC

POWER AND GROUNDING

AMP

ADS-943

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 to +5

Volts

Lead Temperature (10 seconds)

+300

°C

PHYSICAL/ENVIRONMENTAL

PARAMETERS

MIN.

TYP.

MAX.

UNITS

Operating Temp. Range, Case

ADS-943MC, GC

+70

°C

ADS-943MM, 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)

+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

280

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

+1.5

LSB

Full Scale Absolute Accuracy

±0.15

±0.4

±0.15

±0.4

±0.6

%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

±0.5

±0.2

±0.5

±0.4

±1.25

No Missing Codes (f

= 10kHz)

Bits

DYNAMIC PERFORMANCE

Peak Harmonics (0.5dB)

dc to 500kHz

500kHz to 1MHz

1MHz to 1.5MHz

Total Harmonic Distortion (0.5dB)

dc to 500kHz

500kHz to 1MHz

1MHz to 1.5MHz

Signal-to-Noise Ratio

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

500kHz to 1MHz

1MHz to 1.5MHz

Signal-to-Noise Ratio

(& distortion, 0.5dB)
dc to 500kHz

500kHz to 1MHz

1MHz to 1.5MHz

Noise

125

µVrms

Two-Tone Intermodulation

Distortion (f

= 975kHz,

1.2MHz, f

= 3MHz, 0.5dB)

Input Bandwidth (3dB)

Small Signal (20dB input)

MHz

Large Signal (0dB input)

MHz

Feedthrough Rejection (f

= 1.5MHz)

Slew Rate

±400

V/µs

Aperture Delay Time

Aperture Uncertainty

ps rms

FUNCTIONAL SPECIFICATIONS

= +25°C, ±V

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

ADS-943

+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)

208

215

208

215

208

215

Overvoltage Recovery Time

100

333

100

333

100

333

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

+210

+230

+210

+230

+210

+230

5V Supply

125

145

125

145

125

145

Power Dissipation

1.7

1.9

1.7

1.9

1.7

1.9

Watts

Power Supply Rejection

±0.05

%FSR/%V

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 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 minumum limits are +4.75V and 4.75V when
operating at +125°C.

TECHNICAL NOTES

1. Obtaining fully specified performance from the ADS-943

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-943 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.

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.

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.

Contact DATEL for other input voltage ranges.

A 3MHz clock with a 20nsec positive pulse width is used for all production testing.
When sampling at 3MHz, the start convert pulse must be between 10 and
110nsec wide or between 160 and 300nsec wide. The falling edge must not occur
between 110 and 160nsec. For lower sampling rates, wider start pulses may be
used.

Figure 2. Optional ADS-943 Gain Adjust Calibration Circuit

To Pin21
of ADS-943

SIGNAL

INPUT

GAIN

ADJUST

1.98k

+5V

ADS-943

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-943'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-943 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.

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.

Figure 3. Connection Diagram

0.1µF

4.7µF

22, 13

ADS-943

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

INPUT VOLTAGE

ZERO ADJUST

GAIN ADJUST

RANGE

+1/2 LSB

+FS 1½ LSB

±2V

+122µV

+1.99963V

Table 1. Gain and Zero Adjust

BIPOLAR

INPUT VOLTAGE

OFFSET BINARY

SCALE

(±2V RANGE)

MSB

LSB

+FS 1 LSB

+1.99976

11 1111 1111 1111

+3/4FS

+1.50000

11 1000 0000 0000

+1/2FS

+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

ADS-943

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. ADS-943 Timing Diagram

OUTPUT

DATA

Data N Valid

Scale is approximately 20ns per division. Sampling rate = 3MHz.

EOC

Data N-1 Valid

Data N+1 Valid

Invalid

Data

283ns typ.

35ns typ.

130ns

The start convert positive pulse width must be between either 10 and 110nsec or
160 and 300nsec (when sampling at 3MHz) to ensure proper operation. For sampling
rates lower than 3MHz, the start pulse can be wider than 300nsec, however a minimum
pulse width low of 30nsec should be maintained. A 3MHz clock with a 20nsec positive
pulse width is used for all production testing.

Note:

10ns max.

INTERNAL S/H

10ns typ.

Acquisition Time

125ns typ.

208ns typ.

215ns max.

Hold

Conversion Time
120ns min., 130ns typ.,
140ns max.

50ns typ.

30ns typ.

125ns typ.

START

CONVERT

N+1

333nsec

20ns typ.

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