Novel High Efficiency Power Amplifier Mode Using Open Circuit Harmonic Loading

This paper introduces the Class O
²
power amplifier (PA) with high power-density and drain efficiency. A new waveform engineering-based design approach is proposed to realize a reliable high-efficiency PA operation while tuning both second and third harmonic impedances to open-circuit termination. The proposed theory derives the intrinsic current and voltage waveforms as a function of input second-harmonic tuning which is adopted to enable the realization of reliable Class O
²
PA operation. A multi-harmonic vector load-pull system is used for the practical validation that is carried out using a 10-W gallium nitride (GaN) transistor. On load-pull, the Class O
²
mode demonstrates a drain efficiency of 87% at an output power of 39.8 dBm with a gain of 10 dB at a frequency of 1.0 GHz.