In this paper the concept of IAM is introduced and the method Used for analyzing H. F. small signal amplifier is discussed. The expressions of gain and input impedance of amplifier are given.

RF PA almost working in large signal, so it's circuit design methods and transistor used are different from microwave small signal amplifier, these will led to RF PA design become more difficulty.

The paper introduced a design of CMOS amplifier that is used in small signal testing.