High-frequency FET noise parameters and approximation of the optimum source admittance

High-frequency noise parameters of junction FETs and MOSFETs have been determined experimentally. It is shown that the usual noise specifications given in present-day data sheets are not sufficient to describe the noise behavior. A very important noise parameter is the source admittance. However, the exact evaluation of the optimum source admittance, which yields the minimum noise figure, is very complicated. An approximative method is thus described which gives good results and is in good agreement with the experiment.