FUNCTIONAL BLOCK DIAGRAM
+
–
+
–
+
–
+
–
+
–
50
50
10k
10k
10k
10k
V
B
–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.
