Patent ID: 7548114

Claim:
An apparatus for slew rate enhancement of an operational amplifier comprising: an operational amplifier having an input stage, a control stage and an output stage, wherein said input stage receives an input signal; said operational amplifier processes and amplifies said input signal and then outputs an output signal from an output terminal of said output stage; said output stage is formed via cascading a push transistor and a pull transistor; said push transistor is controlled by a push control node of said control stage, and said pull transistor is controlled by a pull control node of said control stage; an auxiliary control device coupled to said push control node and said pull control node of said control stage, mirroring a current of said output stage and comparing the mirrored current with a reference current to generate an auxiliary push control signal and an auxiliary pull control signal; and an auxiliary output device coupled to said output stage of said operational amplifier and controlled by said auxiliary push control signal and said auxiliary pull control signal of said auxiliary control device, wherein when said output voltage is different from said input voltage, said auxiliary control device turns on said auxiliary output device to provide an auxiliary output current for said output terminal; when said output voltage is equal to said input voltage, said auxiliary output device is turned off, and none said auxiliary output current is provided.