Monte Carlo determination of the intrinsic small-signal equivalent circuit of MESFET´s

A Monte Carlo technique for the determination of the intrinsic elements of a broad-band small-signal equivalent circuit (SSEC) of MESFET´s (and FET´s in general) is described. The values of the different elements are calculated from the Y parameters of the intrinsic MESFET, which are obtained from the Fourier analysis of the device transient response to voltage-step perturbations at the drain and gate electrodes. An accurate estimator of the instantaneous currents at the terminals is used, which guarantees the precision of the method. Three different MESFET geometries have been analyzed. For low drain currents under saturation the intrinsic elements are found to be independent of frequency in the whole range of device operation. This fact validates the technique and the proposed equivalent circuit under these conditions. However, for high drain currents the gate-drain capacitance and the drain conductance depend on frequency due to the appearance of charge-accumulation effects