Operational amplifier having offset cancel function

An operational amplifier, which generates an output voltage at an output terminal equal to an input voltage having:

• a differential circuit, which has first and second input transistors whose sources are connected, a current source connected with the sources, and a current mirror circuit connected with the drains of the first and second input transistors;
• a first output transistor, which has a gate controlled by a drain of the second input transistor that being supplied with an input voltage, and a drain that is fed back to a gate of the first input transistor during operational amplifier operation;
• an offset cancel circuit, which is connected with said differential circuit and which stores an offset state of said pair of input transistors;
• and
• a second output transistor, which is provided in parallel with said first output transistor,
• wherein, in the offset cancel period, drains of said first and second output transistors are isolated such that the output terminal is driven by the second output transistor, and, in the operational amplifier operation period following the offset cancel period, said output terminal is driven by said first output transistor.