Effect of Input Harmonic Termination on High Efficiency HBT Amplifiers for Mobile Communications

The effect of an input harmonic termination on a HBT was investigated by simulation and waveform measurement. It was found that the best phase of the input reflection coefficient in the 2nd harmonic(?s2fo) for high efficiency is from 180 to 240 degrees in class F operation. The best phase increases in accordance with the decrease of |?s2fo|. The relationship between the best phase of ?s2fo and |?s2fo| is described by considering the current in the diode and capacitance between the base and emitter in the HBT.