Extraction of a nonlinear AC FET model using small-signal S-parameters

The nonlinearities of an RF FET can be obtained by a set of small-signal circuit elements extracted over a range of terminal voltages and temperatures. This study used pulsed S-parameter measurements on a 3 x 3 dc-bias-point grid at two different temperatures to obtain electrical and electrothermal nonlinearity coefficients up to the third order. The extracted nonlinear ac model can be used in Volterra analysis to gain an insight into distortion mechanisms. The measurement results were in good agreement with the calculated third-order intermodulation values.