US Patent 7508265 Rail-to-rail class-AB operational amplifier

A rail-to-rail class-AB operational amplifier includes a first differential pair unit for receiving a pair of differential signals and generating a first control signal; a second differential pair unit for receiving the pair of differential signals and generating a second control signal; and an output stage for receiving the first control signal and the second control signal and then generating an output voltage. The first differential pair unit includes a first active load, a first transistor differential pair and a first current source. The second differential pair unit includes a second current source, a second transistor differential pair and a second active load. The output stage includes a third current source, a fourth current source and a parallel transistor pair disposed between a second terminal of the third current source and a first terminal of the fourth current source, a first output transistor and a second output transistor, and generates the output voltage according to the first control signal and the second control signal.