Efficiency enhanced class-E power amplifier using the second harmonic injection at the feedback loop

In this paper, the class-E power amplifier with feedback loop driven by the second harmonic injection is studied. The feedback loop is composed of auxiliary class-E amplifier to drive the second harmonic injection, filter to pass second harmonic, and delay line. This power amplifier presents improved PAE (power added efficiency) compared to that without the second harmonic feedback loop because second harmonic feedback loop assists the main amplifier working with conditions for ideal class-E operation. When second harmonic with proper magnitude and phase for ideal class-E conditions is injected to gate of the main amplifier, PAE is improved by 16% compared to that of the class-E amplifier without the second harmonic feedback. The measured maximum output power at the fundamental frequency shows 19.3 dBm, whereas the PAE shows 79 % with 3 dBm input power. The operating frequency of the proposed class-E PA is chosen as 1.95GHz.