Patent ID: 7652533

Claim:
An operation amplifier (OP amplifier), comprising: an input switching unit for receiving a plurality of input voltages and selectively outputting one of the input voltages; an input stage, for receiving the input voltage from the input switching unit, and generating an internal voltage according to the input voltage; and an output stage, for receiving and gaining the internal voltage, so as to output an output voltage, wherein the output stage comprises: a first transistor, having a first source/drain terminal coupled to a first voltage, a second source/drain terminal, and a gate terminal controlled by the internal voltage, wherein the output stage outputs the output voltage according to a voltage at a second source/drain terminal of the first transistor; a plurality of first capacitors; and a first switching unit, adapted for selectively connecting one of the first capacitors between the gate terminal and the second source/drain terminal of the first transistor.