FUNCTIONAL BLOCK DIAGRAM

+

–

+

–

+

–

50

50

10k

10k

10k

10k

–INPUT

–GAIN

SENSE

+INPUT

–GAIN

DRIVE

+GAIN

SENSE

+GAIN

DRIVE

SENSE

OUTPUT

REFERENCE

AD625

REV. D

Information furnished by Analog Devices is believed to be accurate and

reliable. However, no responsibility is assumed by Analog Devices for its

use, nor for any infringements of patents or other rights of third parties

which may result from its use. No license is granted by implication or

otherwise under any patent or patent rights of Analog Devices.

a

Programmable Gain

Instrumentation Amplifier

AD625

One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.

Tel: 781/329-4700

World Wide Web Site: http://www.analog.com

Fax: 781/326-8703

© Analog Devices, Inc., 2000

FEATURES

User Programmed Gains of 1 to 10,000

Low Gain Error: 0.02% Max

Low Gain TC: 5 ppm/ C Max

Low Nonlinearity: 0.001% Max

Low Offset Voltage: 25

V

Low Noise 4 nV/

√Hz (at 1 kHz) RTI

Gain Bandwidth Product: 25 MHz

16-Lead Ceramic or Plastic DIP Package,

20-Terminal LCC Package

Standard Military Drawing Available

MlL-Standard Parts Available

Low Cost

PRODUCT DESCRIPTION

The AD625 is a precision instrumentation amplifier specifically

designed to fulfill two major areas of application: 1) Circuits re-

quiring nonstandard gains (i.e., gains not easily achievable with

devices such as the AD524 and AD624). 2) Circuits requiring a

low cost, precision software programmable gain amplifier.

For low noise, high CMRR, and low drift the AD625JN is the

most cost effective instrumentation amplifier solution available.

An additional three resistors allow the user to set any gain from

1 to 10,000. The error contribution of the AD625JN is less than

0.05% gain error and under 5 ppm/

°C gain TC; performance

limitations are primarily determined by the external resistors.

Common-mode rejection is independent of the feedback resistor

matching.

A software programmable gain amplifier (SPGA) can be config-

ured with the addition of a CMOS multiplexer (or other switch

network), and a suitable resistor network. Because the ON

resistance of the switches is removed from the signal path, an

AD625 based SPGA will deliver 12-bit precision, and can be

programmed for any set of gains between 1 and 10,000, with

completely user selected gain steps.

For the highest precision the AD625C offers an input offset

voltage drift of less than 0.25

µV/°C, output offset drift below

15

µV/°C, and a maximum nonlinearity of 0.001% at G = 1. All

grades exhibit excellent ac performance; a 25 MHz gain band-

width product, 5 V/

µs slew rate and 15 µs settling time.

The AD625 is available in three accuracy grades (A, B, C) for

industrial (–40

°C to +85°C) temperature range, two grades (J,

K) for commercial (0

°C to +70°C) temperature range, and one

(S) grade rated over the extended (–55

°C to +125°C) tempera-

ture range.

PRODUCT HIGHLIGHTS

1. The AD625 affords up to 16-bit precision for user selected

fixed gains from 1 to 10,000. Any gain in this range can be

programmed by 3 external resistors.

2. A 12-bit software programmable gain amplifier can be config-

ured using the AD625, a CMOS multiplexer and a resistor

network. Unlike previous instrumentation amplifier designs,

the ON resistance of a CMOS switch does not affect the gain

accuracy.

3. The gain accuracy and gain temperature coefficient of the

amplifier circuit are primarily dependent on the user selected

external resistors.

4. The AD625 provides totally independent input and output

offset nulling terminals for high precision applications. This

minimizes the effects of offset voltage in gain-ranging

applications.

5. The proprietary design of the AD625 provides input voltage

noise of 4 nV/

√Hz at 1 kHz.

6. External resistor matching is not required to maintain high

common-mode rejection.