A Verilog-A Large-Signal GaN HEMT Model for High Power Amplifier Design

This paper describes the high-power non-linear modeling of a GaN HEMT device using a Verilog-A-implemented and modified version of the EEHEMT model commonly found in commercial simulators. As discussed in, peculiarities of GaN device physics exposed flaws in the standard EEHEMT model such as the inability to describe trap-related phenomena such as knee walk-out, multiple voltage dependencies of conduction currents, anomalies in the saturation current/conductance, and nonlinear behavior of source resistance. Improvements were made to the standard model to accommodate GaN-specific characteristics of the knee and saturation regions of the device IV plane as well as a functional dependence of Rs on RF operating current. Additionally, temperature dependencies were implemented in the Verilog-A version using a thermal sub-circuit to account for self-heating in real-time and ambient temperature effects. Extensive pulsed and CW load-pull measurements were done at multiple source/load states and power levels and at several frequencies. Output power, gain, efficiency and load-pull contour simulations vs. measurements are presented. The improved model is shown to accurately predict actual device and scaled high-power amplifier behavior and has proven to be a useful tool in very high power product design.