High-efficiency power amplifier design

High efficiency of the power amplifier can be obtained by using Class-F and Class-E operation modes or their different approximations, depending on the technical requirements. In all cases, an efficiency improvement in practical implementation is achieved by providing the nonlinear operation conditions when an active device can operate in pinch-off and saturation regions during most of the period, resulting in the nonsinusoidal collector current and voltage waveforms, symmetrical for Class-F and asymmetrical for Class-E operation modes. In Class-F power amplifiers analyzed in frequency domain, the fundamental-frequency 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. In Class-E power amplifiers analyzed in time domain, an efficiency improvement is achieved by realizing the on/off active device switching operation (saturation and pinch-off regions) with special current and voltage waveforms so that high voltage and high current do not concur at the same time.