The Pospieszalski noise model and the imaginary part of the optimum noise source impedance of extrinsic or packaged FET´s

The imaginary part X(S_opt) of the optimum noise impedance for extrinsic or packaged devices is investigated. The analysis modifies the well-known Pospieszalski noise model by applying a series feedback to the source port. A simple expression for X(S_opt ) is developed and is verified for extrinsic and packaged devices with a decreasing level of accuracy. The results give further insights into the way the parasitic inductors L_g and L_s affect the noise performance of the transistor and can help to design low-noise amplifier with simultaneous signal and noise power match at the input port