Patent ID: 7737782

Claim:
A CMOS operational amplifier circuit, comprising: a differential input circuit part; and a folded cascode circuit part, wherein the differential input circuit part comprises: a p-type MOS transistor differential pair and an n-type MOS transistor differential pair, which have a positive input terminal and a negative input terminal in common; a first constant current circuit that supplies an operation current to the p-type MOS transistor differential pair and the n-type MOS transistor differential pair; and a current changeover circuit that supplies the operation current of the first constant current circuit to the p-type MOS transistor differential pair and the n-type MOS transistor differential pair in turn, wherein the folded cascode circuit part comprises: a cascode connection current mirror circuit; a second constant current circuit and a third constant current circuit, which are connected in series with the cascade connection current mirror circuit; and a bias voltage source that applies a bias voltage to the cascode connection current mirror circuit, and wherein the bias voltage source increases the bias voltage when the operation current flows in the n-type MOS transistor differential pair.