Operational amplifier (op amp) is an electronic integrated circuit with multi-stage amplifier circuit, and its input stage is a differential amplifier circuit, which has high input resistance and the ability to suppress zero drift. The intermediate stage is mainly used for voltage amplification, which has a high voltage amplification factor and is generally composed of a common emitter amplifier circuit; The output electrode is connecte with that load, and has the characteristics of strong load-carrying capacity and low output resistance. Operational amplifiers are widely used.