An instrumentation amplifier (InAmp) is an integrated circuit or operational amplifier topology that has high input impedance differential inputs and a low impedance single-sided output. Because of precision laser-trimming techniques for passive circuit elements, InAmps implemented as integrated circuits can achieve impressive common mode rejection ratios, while discrete OpAmp implementations can be disappointing in this regard.
Recommended reading
A Designer's Guide to Instrumentation Amplifiers, written at Analog Devices Inc. by Charles Kitchin and Lew Counts, gives a comprehensive overview of Instrumentation Amplifier technology and application. This classic text is available free of charge.
Three-OpAmp Instrumentation Amplifiers: Advantages & Disadvantages
