Analytic solution of the velocity-saturated MOSFET/MODFET wave equation and its application to the prediction of the microwave characteristics of MODFETs

An AC model for the saturated MODFET is reported. The MOSFET/MODFET wave equation accounting for velocity saturation and channel length modulation is derived. An exact solution of the wave equation is obtained in terms of Bessel functions. A frequency power series is used to derive analytic expressions for the intrinsic Y-parameters. This AC model is applied to the prediction of the microwave characteristics of 1- mu m AlGaAs/GaAs MODFETs and GaAlAs/InGaAs/GaAs pseudomorphic MODFETs. The parameters used by the AC model are extracted by fitting the I-V characteristics. The parasitics are either estimated or measured. A good prediction of the scattering parameters measured from 2 to 18.4 GHz is achieved for different biases. The deviation of the calculated unilateral power gain from the measured values was on average 1.25 and 2.18 dB for the conventional MODFET and the pseudomorphic MODFET, respectively.<
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