Patent ID: 7737790

Claim:
A cascode amplifier, comprising: an input signal terminal; an output signal terminal; a first transistor and a second transistor, wherein each of the first and the second transistors has a gate electrode, a first electrode and a second electrode, the first electrode of the first transistor is coupled to the second electrode of the second transistor, the gate electrode of the first transistor is coupled to the input signal terminal, and the first electrode of the second transistor is coupled to the output signal terminal; a third transistor and a fourth transistor, wherein each of the third and the fourth transistors has a gate electrode, a first electrode and a second electrode, the first electrode of the third transistor is coupled to the second electrode of the fourth transistor, and the gate electrodes of the third and the fourth transistors are coupled to the gate electrodes of the first and the second transistors, respectively; and a bias circuit, coupled to the first electrode of the fourth transistor, for biasing a voltage level at the first electrode of the fourth transistor to make the second and the fourth transistors operate in a same region.