CMRR analysis of instrumentation amplifiers

A set of the simple and practical expressions for the CMRR of instrumentation amplifiers (IAs) based on 2, 3 and 4 opamps is given. These equations take into account not only mismatch of determined resistors but also the limited value of the CMRR of op-amps used. The derived equations are very useful for tolerance analysis which is shown on the example of the 3-op-amp IA