Statistical harmonic load termination analysis of switch-mode power amplifiers employing bandpass-pulse-length modulation

This paper presents a method to determine optimum load impedances from a statistical analysis of a harmonic load pull simulation for a switch-mode power amplifier fed with a bandpass-pulse-length modulated signal. The variability of the duty cycle caused by the modulation was taken into account. Thereby, the crucial impact of the phase angle of the filter input reflection coefficient on the achievable efficiency is shown. The simulation was carried out for a 0.25 µm gate length GaN based current-switching power amplifier. Based on the simulation results, a microstrip line network working as reconstruction filter was designed and fabricated. The demonstrator comprising the switch-mode power amplifier monolithic microwave integrated circuit and reconstruction filter achieved a drain efficiency and RF output power of up to 71.1% and 36.7dBm (4.6 W), respectively, over a frequency range from 870 MHz to 930 MHz.