Control circuit for operational amplifier and method thereof

A control circuit for an operational amplifier and a method thereof are provided to modulate the dynamically for the high driving capability and the power saving. The control circuit comprises a bias unit coupled to the operational amplifier and a control unit coupled to the bias unit. The bias unit normally outputs a bias signal to bias the operational amplifier to make the operational amplifier having a first driving capability. Whenever is needed to modulate, the control unit receives a modulating signal and outputs a control signal according to the modulating signal. When the bias unit receives the control signal, the bias unit dynamically modulate the bias signal according to the control signal, and the driving capability of the operational amplifier is modulated indirectly by the modulated bias signal.