Analysis of High-Efficiency Power Amplifiers With Arbitrary Output Harmonic Terminations

This paper presents an analysis of ideal power amplifier (PA) efficiency maximization subject to a finite set of arbitrary complex harmonic terminations, extending previous results where only purely reactive harmonic terminations were treated. Maximum efficiency and corresponding fundamental output power and load impedance are analyzed as a function of harmonic termination(s). For a PA restricted to second harmonic drain waveform shaping, maximum efficiency as a function of second harmonic termination is treated for cases of both purely real and complex fundamental frequency impedances. For the case of a PA restricted to second and third harmonic drain waveform shaping, peak efficiency as a function of third harmonic impedance with an ideal second harmonic termination is analyzed. Additionally, the sensitivity of PA efficiency with respect to the magnitude and phase of the second and third harmonic load reflection coefficients is examined. The analysis is extended to include device and package parasitics. The paper concludes with a discussion of how the presented general analysis method provides useful insights to the PA designer.