Design of Class F Power Amplifiers Using Cree GaN HEMTs and Microwave Office Software to Optimize Gain, Efficiency, and Stability

This white paper explores the design of power amplifiers employing Cree GaN HEMTs to maximize power-added efficiency (PAE) by optimizing source and load pull at both fundamental and harmonic frequencies. The load-pull scripts that are available in Microwave Office circuit design software have been used extensively to find the optimum trade-offs in power gain, efficiency, and stability. The paper will specifically describe the basis of Class F PA and inverse Class F design F, as well as a relatively new approach called continuous Class F, which enables greater bandwidths to be realized. Design examples are given, including the inspection of voltage and current waveforms for both packaged and bare die transistors in the 10 to 25 watt power range for frequencies up to 2.5 GHz.