Characterization of GaN Transistors and PAs with Modulated Signals

An analysis of Gallium Nitride (GaN) transistor and power amplifiers (PAs) behavior under modulated signal excitation is presented. Using a passive load-pull system and a large-signal vector network analyzer with an Arbitrary Wave-form Generator (AWG) wideband source, we characterize two 6 W GaN-on-SiC transistors from different manufacturers under various excitations. Experimental results with 300-tone 6.1 MHz bandwidth signals indicate that the power-added efficiency, output power, and gain of transistors with narrowband OFDM-like signals are sufficiently represented by their CW performance at the same mean power. Additionally, a PA is characterized with different numbers of 10-MHz multi-carrier signals, evenly spaced within a 500 MHz bandwidth centered around a 4.35 GHz carrier. The single-stage hybrid GaN PA is designed with CW output power above 10 W from 4 to 5 GHz and with PAE exceeding 50% from 4.1-4.6 GHz with a saturated gain above 8dB at 28 V drain bias. The efficiency, output power, noise power ratio, and spectral efficiency are quantified in measurement and show that the overall performance can be appropriately defined by an equally-weighted figure of merit which is a function of the number of modulated signals.