Instrumentation amplifier

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You may be looking for instrument amplifier, as used for amplifying musical instruments. This page is about the electronic device.

An instrumentation amplifier is a type of differential amplifier that has been specifically designed to have characteristics suitable for use in measurement and test equipment. These characteristics include very low DC offset, low drift, low noise, very high open-loop gain, very high common-mode rejection ratio, and very high input impedances. They are used where great accuracy and stability of the circuit both short- and long-term are required.

The most commonly used instrumentation amplifier circuit is shown in the figure. The gain of the circuit is

The ideal common-mode gain of an instrumentation amplifier is zero. In the circuit shown, common-mode gain is caused by mismatches in the values of the equally-numbered resistors and by the non-zero common mode gains of the two input op-amps. Obtaining very closely matched resistors is an important difficulty in fabricating these circuits, as is optimizing the common mode performance of the input op-amps. See - Smither, Pugh and Woolard: ‘CMRR Analysis of the 3-op-amp instrumentation amplifier', Electronics letters, 2nd February 1989.

Instrumentation amplifiers can be built with individual op-amps and precision resistors, but are also available in integrated circuit form from several manufacturers (including Texas Instruments, Analog Devices, and Linear Technology). An IC instrumentation amplifier typically contains closely matched laser-trimmed resistors, and therefore offers excellent common-mode rejection.

[edit] See also

• Operational amplifier
• Operational amplifier applications

[edit] External links

• Synectic Design - Amplifier designers and manufacturers
• Opamp Instrumentation Amplifier
• The instrumentation amplifier
• Bioengineering Breadboard I: Instrumentation Amplifier
• Lessons In Electric Circuits — Volume III — The instrumentation amplifier
• A Practical Review of Common Mode and Instrumentation Amplifiers (PDF)
• The Instrumentation Amplifier