ANALYTICAL METHOD FOR DETERMINING EQUIVALENT-CIRCUIT PARAMETERS OF GAAS-FETS

An analytical method has been developed that gives a simple and practi cal means of extracting small-signal equivalent circuit parameters (EC P's) of GaAs FET's with negligibly small bond-pad capacitances. Only t he S-parameter measurement of the pinched-off cold field-effect transi stor (FET) is enough to determine the extrinsic FET ECP's. The intrins ic FET ECP's of a medium-power Ku-band GaAs FET chip with a total gate width of 800 mu m have been analytically extracted for two types of e ight-element intrinsic FET models; Model 1 (Curtice model) and Model 2 that differ in the control voltage (V-G) definition, Model 2 with V-G defined across the gate-source capacitance is found more appropriate judging from the smaller frequency dependence of the ECP's and a bette r agreement between the calculated and measured S-parameters over 2-20 GHz.