Two-stage rail-to-rail operational amplifier

Abstract

A two-stage class-AB operational amplifier, that can be implemented either with bipolar or MOS transistors, includes a differential input circuit adapted to receive a differential input signal to produce an amplified differential output signal for application to first and second nodes. The differential input stage has a common-mode control circuit that produces first and second common-mode control voltages on the first and second nodes. The common-mode control voltages are combined with the amplified differential output signal on the first and second nodes to produce a first stage differential output signal. A high-swing output stage is connected to receive the first stage differential output signal. First and second current mirrors each have a mirror transistor to mirror an output current produced in response to the differential input signals on respective lines including the first and second nodes. The common-mode control circuit is in series with mirror transistors of the first and second current mirrors. A circuit clamps the first and second nodes at a voltage of 2V.sub.BE below the supply voltage, and clamps the voltage at the second node at a voltage of 2V.sub.BE above the reference potential, enabling the circuit to operate with improved power-supply rejection ratios.

Dependencies are inferred from the claim text.