Experimental study on effect of second-harmonic injection at input of classes F and F-1 GaN power amplifiers

This presented study focuses on the impact of gate-source voltage waveforms on power added efficiency performances of GaN HEMTs for the design of class F and class F^-1 amplifiers. It is shown that second-harmonic signal injection at the gate port of transistors can lead to efficiency improvements in the case of class F operation and efficiency deteriorations in the case of class F^-1 operation. This work is applied to a 15 W GaN HEMT die from Cree at a fundamental frequency Fo equal to 2 GHz. Calibrated on-wafer time domain measurements are reported.