Source follower

A source follower, which can increase the voltage swing of the input terminal and overcome the insufficient driving capability of the typical source follower, includes a first current source, a first transistor, a second current source, a second transistor, a third current source and a third transistor, and uses the counteraction of the gate-source voltages (Vgs2 and Vgs3) of the second and third transistors to increase the voltage swing of the input terminal to the first transistor. Accordingly, the circuit is not likely to have the saturation effect on its input terminal due to the increased voltage swing of the input voltage, thereby avoiding occurrence of distortion.