Patent ID: 7786801

Claim:
An operational amplifier comprising: a differential amplifier generating a first current through a first output node and a second current through a second output node in response to a voltage difference between a first input signal input through a first input terminal and a second input signal input through a second input terminal; an output stage generating an output signal through an output node; and a control unit receiving a voltage of the first output node and a voltage of the second output node, as bias voltages, and controlling an output current of the output stage to determine the output signal of the output stage in response to the received voltages of the first and second output nodes, wherein the control unit comprises: a first self biased cascode current mirror connected between the first output node, a first control node, and a first power source; a second self biased cascode current mirror connected between the second output node, the first power source, and an intermediate node; a third self biased cascode current mirror connected between the intermediate node, a second power source, and a second control node; and a bias circuit connected between the first control node and the second control node and controlling each of a voltage of the first control node and a voltage of the second control node based on the voltage of the first output node and a voltage of the intermediate node.