A New GaN HEMT Equivalent Circuit Modeling Technique Based on X-Parameters
This paper reviews three modern transistor modeling flows enabled by large-signal waveform and/or X-parameter<sup>1</sup> measurements from a commercially available nonlinear vector network analyzer (NVNA) instrument. NVNA transistor characterization more safely exercises the device over a wider operating domain than is possible with conventional DC and linear S-parameter measurements, is more indicative of the device large-signal response in actual use conditions, provides data at much faster timescales than pulsed I-V methods, and provides large-signal model validation as a free additional benefit. In the first flow considered, NVNA waveform data is used as a target to extract and tune compact model parameter values and for model validation under large-signal conditions. In the second flow, NVNA waveform data is used to directly construct the multi-variate nonlinear current-source and charge-based nonlinear capacitor functions of an advanced electrothermal and trap-dependent compact model suitable for GaAs and GaN FETs, effectively bypassing the need for explicit model constitutive relation formulation. The final approach is based on the X-parameter measurement and behavioral modeling framework supported by the NVNA, producing nonlinear transistor models directly in the frequency domain. Recent advances in X-parameter methods for transistors, including simple scalability with geometry, show early potential for useful device models, under certain conditions, without the requirement of specifying an internal topology or equivalent circuit at all.