Patent ID: 7253679
Filing Date: 2007-08-07
Classification: H03F

Abstract:
1. An operational amplifier comprising: an input terminal and an output terminal connected to the input terminal for outputting output voltage; an operational amplifier circuit including a current mirror, having a first pair of transistors, and a first differential input unit, having a second pair of transistors connected to the current mirror; an offset adjustment circuit including a second differential input unit having a third pair of transistors connected to the current mirror; a first switch for switching between a first connection point, in which a gate of one of the second pair of transistors is connected to a gate of the other one of the second pair of transistors, and a second connection point, in which the gate of the one of the second pair of transistors is connected to the input terminal; a second switch for switching between a connection state, in which a gate of one of the third pair of transistors is connected to the input terminal, and a disconnection state, in which the gate of the one of the third pair of transistors is disconnected from the input terminal; and an offset voltage holding unit, connected to gates of the third pair of transistors, for holding an offset voltage derived from output voltage generated by the operational amplifier circuit when the first switch is switched to the first connection point and the second switch is switched to the connection state, the offset voltage holding unit generating a potential difference between the gates of the third pair of transistors in accordance with the held offset voltage when the first switch is switched to the second connection point and the second switch is switched to the disconnection state.