Patent ID: 7714656

Claim:
An operational amplifier comprising: an input amplifier configured to amplify at least one differential input signal; a first common mode feedback amplifier configured to amplify a first common mode voltage; a cascode amplifier configured to cascade-amplify output signals from the input amplifier and the first common mode feedback amplifier; a first common mode voltage generator configured to generate a central voltage of the output signal from the cascade amplifier and input the central voltage to the first common mode feedback amplifier; a frequency compensator configured to feedback the output signal of the cascode amplifier to the first common mode feedback amplifier so as to compensate a frequency of the first common mode feedback amplifier; an output amplifier configured to generate a differential output signal by amplifying the output signal of the cascode amplifier; a second common mode voltage generator configured to generate a second common mode voltage using a central voltage of the differential output signal output by the output amplifier; and a second common mode feedback amplifier configured to amplify the second common mode voltage generated by the second common mode voltage generator and to feedback the amplified second common mode voltage to the output amplifier.