Support high-gain applications using rejustors and precision instrumentation amplifiers

Overview

Instrumentation amplifiers are used in a wide variety of applications. When the instrumentation amplifier is connected to a sensor with a weak differential signal output, the instrumentation amplifier needs to provide high gain, and requires high precision gain while maintaining a very low offset voltage. Under certain conditions, the differential signal output by the sensor is only a few millivolts, and the amplifier gain needs to be as high as 1,000 times.

Some instrumentation amplifiers have built-in gain adjustment resistors and have several fixed gain settings to choose from. However, when design flexibility is required and the amplified sensor signal must match the full-scale range of the analog-to-digital converter, designers prefer to use instrumentation amplifiers that set the gain by adjusting external voltage divider resistors. In this case, it is important to note that even the most accurate instrumentation amplifier will suffer from errors in the external gain setting resistor that will affect the amplifier's performance.

This article describes how to design a high-precision application using a zero-drift precision instrumentation amplifier, a pair of rejustors, and gain-setting resistors.