Chapter 9 - Alternative and Mixed-Mode High-Efficiency Power Amplifiers

Abstract

In Chapter 9, the different alternative and mixed-mode configurations of high efficiency power amplifiers are presented. A Class-DE power amplifier is based on the combination of a voltage-switching Class-D mode with Class-E switching conditions, thus extending the switching Class-D operation to higher frequencies. Effects of the saturation resistance and nonlinear capacitance, driving waveforms, and some practical examples of Class-DE power amplifiers are discussed. The switchmode Class-FE or Class-E/F power amplifier can provide lower voltage peak factors when zero voltage and zero voltage-derivative conditions corresponding to Class-E mode, required to eliminate discharge loss of the shunt capacitance, are accompanied by harmonic tuning using the resonant circuits tuned to selected harmonic components realizing Class-F or inverse Class-F mode. Also, the biharmonic Class-E M mode is described, which can eliminate the efficiency degradation of a Class-E operation mode at higher frequencies due to the increased switching power losses with increasing values of the turn-off switching time. An inverse Class-E power amplifier represents an inverse version of a classical Class-E power amplifier with a shunt capacitance where the load-network inductor and capacitor replace each other. Harmonic-control techniques for designing microwave power amplifiers are given with a description of a systematic procedure of multiharmonic load-pull simulation using the harmonic-balance method and an active load-pull measurement system. Finally, outphasing modulation systems are considered where a variable envelope output is created by the sum of two constant-envelope signals with varying phases which therefore can be amplified by a highly efficient power amplifier operated in a switching Class-D, Class-E, or Class-F operation mode, or their combinations.