Isothermal Characterization of Traps in GaN HEMTs Operating in Class B Using a Real-Time Pulsed-RF NVNA Testbed

This article presents a real-time nonlinear vector network analyzer (NVNA) testbed that enables the acquisition of the isothermal transient response of GaN HEMTs operating in pulsed class-B mode with arbitrary loads. An oscilloscope-based architecture and a cost-effective and traceable harmonic phase calibration procedure are presented for the proposed real-time NVNA. The system is configured to realize pulsed multiharmonic active load—pull (ALP) for synthesizing any class of operation. This real-time NVNA is used for the characterization of trapping in GaN HEMTs operating in pulsed class B under verified isothermal operation. It allows for the isothermal acquisition of the RF dynamic loadlines from pulse-to-pulse at different biasing conditions to account for different trapping states and operating temperatures. The capture and emission processes are monitored at each pulse using the quiescent current and RF power for each of the biasing conditions considered. These measurements and associated trap modeling demonstrate that a majority of the capture process is taking place in the first RF pulse (<200 ns) with the residual capture process distributed over various durations depending on the biasing condition and associated temperature. The proposed real-time NVNA combined with pulsed multiharmonic ALP should prove to be a useful tool for studying trapping effects in RF devices.