3.3 Instrumentation Amplifier

Like the Differential Amplifier, instrumentation amplifiers are designed to amplify the difference between two input signals. An instrumentation amplifier uses three operational amplifiers while a differential amplifier uses only two. The configuration implemented in the microcontroller is shown below in Figure 3-3.

Note: Discrete instrumentation amplifiers may use a different circuit implementation that the one in the microcontroller.

Unlike the differential amplifier, the instrumentation amplifier inputs have a matched gain, which makes it easier to calculate the differential voltage when both inputs vary at the same time. However, the instrumentation amplifier configuration is unidirectional - if the inputs are flipped, the output will become ground (see Output Swing for more information). The output formula is shown below:

V_{O U T} = (V_{I N +} - V_{I N -}) * G A I N

Consult the device data sheet for possible gain configurations for this circuit.