Two Op-Amps Instrumentation Amplifier

For standard instrumentation amplifier, a three op-amps instrumentation amplifier circuit is common, but if you need smaller component count and lower cost, you can use just two op-amps for the same function: a high impedance and good CMRR for sensor pre-amplification and buffering. Here is the circuit’s schematic duiagram:

A two-op-amp instrumentation amplifier can also be used to make a high-input impedance DC differential amplifier. As in the two-op-amp circuit, this instrumentation amplifier requires precise resistor matching for good CMRR. R4 should equal to R1 and R3 should equal R2. [Circuit’s schematic diagram source: National Semiconductor’s Application Notes]