Patent ID: 7391263

Claim:
An operational amplifier comprising: an amplifier including a differential pair of first and second transistors and a first current source, the first and second transistors being provided on a side of a high voltage power source and their control electrodes receiving mutually reversed phase, positive and negative side input voltages, respectively, the first current source being provided between the first and second transistors and a low voltage power source to generate a first bias current; a replica amplifier including a differential pair of third and fourth transistors and a second current source, the third and fourth transistors being provided on the side of the high voltage power source and their control electrodes receiving the positive and negative side input voltages, respectively, the second current source being provided between the third and fourth transistors and the low voltage power source; a voltage-current converting circuit supplied with positive and negative side voltages output from the replica amplifier, the voltage-current converting circuit converting the positive and negative side voltages to output currents; and a bias current control circuit that receives the output currents from the voltage-current converting circuit, generates a differential current between the output currents and a reference current and supplies the differential current to the first current source to control the first bias current.