Chapter 10 - Alternative and mixed-mode high-efficiency power amplifiers

Abstract

In this chapter, the different alternative and mixed-mode configurations of high-efficiency PAs are presented and discussed. A Class-DE PA 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 PAs are discussed in detail. The switchmode Class-FE or Class-E/F PA 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-EM 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 PA represents an inverse version of a classical Class-E PA with a shunt capacitance where the load-network inductor and capacitor replace each other. Harmonic-control techniques for designing microwave PAs are given with a description of a systematic procedure of multiharmonic load-pull simulation using the harmonic-balance method and 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 highly efficient PA operated in a switching Class-D, Class-E, or Class-F operation mode, or their combinations.