A small-signal equivalent circuit for the high electron mobility transistor

A novel analytical model geared toward circuit simulation for the AlGaAs/GaAs HEMT (high electron mobility transistor) is presented. The model takes into account the parasitic parallel conduction in AlGaAs, which becomes important for large gate voltages, together with important effects such as mobility degradation, channel length modulation, maximum concentration of the 2-DEG (two-dimensional electron gas), and the series resistances. Expressions for the drain current and the small-signal equivalent circuit parameters are derived. The factors contributing to the transconductance compression are analyzed. The theoretical predictions of the model are compared with experimental data and are found to be in good agreement over a wide range of bias conditions