Patent ID: 8130038

Claim:
A class AB operational amplifier, comprising: a first transistor, for generating a first current; a second transistor, where a second source voltage of the second transistor is equal to a first source voltage of the first transistor, for generating an output stage quiescent current; and an output stage quiescent current controller, coupled to a gate and a drain of the first transistor, for controlling a first drain-to-source voltage of the first transistor to be equal to a second drain-to-source voltage of the second transistor, and comprising: an operational amplifier comparator, for controlling a first drain voltage of the first transistor to be equal to a second drain voltage of the second transistor via negative feedback, comprising: a first input terminal, coupled to the drain of the first transistor; a second input terminal, for receiving a reference voltage, which is equal to the second drain voltage; and an output terminal, coupled to the gate of the first transistor; wherein a ratio of the output stage quiescent current to the first current is equal to a ratio of a second W/L ratio of the second transistor to a first W/L ratio of the first transistor.