Analytical Model of Fast-Switching GaN HEMTs in Bridge-Leg Considering Nonlinear Characteristics

The nonlinear parasitic capacitors and transfer characteristic of GaN HEMT play critical roles in its fast switching transient process, and it could largely determine the end shape of its switching transient waveform. Traditionally, people tend to take advantage of the accessible C-V curve from device datasheet as raw data for curve fitting, which could introduce error in its fast-switching transient analysis. Firstly, C-V data of device datasheet is normally achieved through small-signal test in preset static operating condition, which cannot represent the full dynamic characteristics of device in fast switching transient. Secondly, the bias effect of gate voltage on gate-source capacitor is normally neglected in analytical modeling of GaN HEMT, which could bring some errors during fast switching transients. Moreover, the transfer-characteristics curve provided in device datasheet is generally only about case with low drain-source voltage, and it was observed with obvious difference for higher voltages for some devices. Taking these issues into account, this paper proposes an accurate nonlinear characterization model of GaN HEMT, combined into accurate analytical model of its switching transient analysis in bridge-leg topology. The effectiveness of model was evaluated through experimental results in double-pulse test.