Large-signal modeling of GaNFET and nonlinearity analysis using Volterra series

A large-signal model is reported to investigate the nonlinearities of a GaN MESFET. The model developed accounts for the observed current collapse and frequency dispersion of output resistance and transconductance and uses Volterra series technique to determine the nonlinearities. Calculated f(T) and f(max) of a 0.8 mum x 150 mum GaN MESFET are 6.5 GHz and 13 GHz, respectively, and are in close agreement with their measured values of 6 GHz and 14 GHz, respectively. For a 1.0 mum x 150 mum FET operating at 1 GHz, l-dB compression point and output referred third-order intercept point (OIP3) are 18 dBm and 25.3 dBm, respectively. The corresponding quantities are 19.6 dBm and 30.5 dBm for a 0.6 mum x 150 mum FET at same frequency. Similar improvements in third-order intermodulation (IM3) for shorter gate length devices are reported.