Patent ID: 7081792

Claim:
An operational amplifier in which a differential amplifier circuit equipped with a current mirror circuit is incorporated, the operational amplifier comprising: a first switch connected to a portion between an inverted input terminal and a non-inverted input terminal of the differential amplifier circuit; a second switch connected to a portion between an output terminal of the operational amplifier and the inverted input terminal, the second switch controlling conductive state and non-conductive state contrary to the first switch; a differential pair input circuit in which a current path terminal for a first transistor and a current path terminal for a second transistor are connected to a first current terminal and a second current terminal of the current mirror, respectively; a third switch connected to a portion between a gate of the first transistor and an output terminal of the operational amplifier, the third switch being set in conductive state while the first switch is in conductive state and being set in non-conductive state while the first switch is in non-conductive state; a first capacitor connected to a portion between a gate of the first transistor and predetermined voltage; a fourth switch connected to a portion between a gate of the second transistor and the output terminal of the operational amplifier, the fourth switch being set in conductive state for a predetermined length of period while the second switch is in conductive state; and a second capacitor connected to a portion between a gate of the second transistor and predetermined voltage, wherein the operational amplifier has offset cancel function.