Understanding Instrumentation Amplifier Vcm vs. Vout Plots

The most common issue when working with instrumentation amplifiers involves the Vcm vs. Vout plot, which defines the linear operating region of the device.  An example from the INA826 data sheet is shown below.

The output swing of most instrumentation amplifiers depends on a number of factors including supply voltage, gain, topology, and reference voltage. The following 3-part article series describes the linear operation of traditional 3-op amp instrumentation amplifiers such as the INA333, INA826, INA827, and INA188.

The following Analog Applications Journal describes the linear operation of 2-op amp instrumentation amplifiers such as the INA122, INA126, INA155, INA156.

The following Analog Applications Journal describes the linear operation of 2-op amp instrumentation amplifiers with an output gain stage, such as the INA321/2 and INA331/2.

The following Analog Applications Journal correlates the theory from the previous 5 articles with measured results.

A downloadable software tool that generates Vcm vs. Vout plots for most 2 and 3-op amp instrumentation amplifiers can be obtained from this link:

The INA326 is an excellent instrumentation amplifier that has true rail-to-rail input and output swing.  In other words the output does not depend on the input common-mode range, gain, or reference voltage.  Please note that it is sensitive to parasitic capacitance placed on the gain setting pins.  Therefore use a PCB for evaluation of the device.