Design of Class AB Micropower Operational Amplifier with Rail-to-Rail Output

A class AB micropower operational amplifier with rail-to-rail output was proposed based on analysis of the input and output stage of class AB operational amplifiers. The folded cascode structure is adopted in its input stage. And a PNP transistor and an NMOS transistor are used as the pull-up and pull-down transistor of its output stage respectively. The operational amplifier features high open-loop gain,low quiescent current and wide-3 dB bandwidth. The circuit was designed and fabricated in 1.5 μm BCD technology. Test results showed that the quiescent current of 8.5 μA,the closed loop bandwidth of 20 kHz and the open-loop gain of 100 dB were successfully achieved.