Chapter 4 - Inverse Class F

Abstract

The efficient operation of power amplifier can be obtained by applying biharmonic or polyharmonic modes when an additional single-resonant or multi-resonant circuit tuned to the even harmonics of the fundamental frequency is added into the load network. An infinite number of even-harmonic resonators result in an idealized inverse Class-F mode with a half-sinusoidal voltage waveform and a square current waveform at the device output terminal. In inverse Class-F power amplifiers analyzed in frequency domain, the fundamental and harmonic load impedances are optimized by short-circuit termination and open-circuit peaking to control the voltage and current waveforms at the device output to obtain maximum efficiency. This chapter analyzes different inverse Class-F techniques using lumped and transmission-line elements, including a quarter-wave transmission line. Design examples and practical radio frequency (RF) and microwave inverse Class-F power amplifiers are also discussed in the chapter.