Small signal nonquasistatic models for GaAs field effect transistors for implementation in SPICE. Part 1: Modulation-doped field effect transistors (MODFETs)

Abstract

A general small signal nonquasistatic model for modulation doped field effect transistors (MODFETs) is presented. The model is valid for devices operating in both linear and saturation regions. The two dimensional electron gas (2DEG) current is modelled. The current flowing in the parasitic doped AlGaAs layer is considered elsewhere. In both cases, admittance parameters (Y-parameters) are derived and used to build SPICE-like equivalent circuits. The proposed model can, therefore, be easily implemented in SPICE for microwave and high frequency analogue circuit analysis. The results show that, for a 1 μm gate length MODFET, the error is less than 5% at 86 GHz.