Digitally-controlled high-efficiency series form switch-linear hybrid supply modulator for envelope tracking power amplifiers

Abstract

This paper presents a digitally-controlled highly efficient supply modulator. This supply modulator is implemented as a multilevel converter in series with a linear amplifier. The multilevel converter output which controlled by digital signals is employed to supply the linear amplifier. The digitally controlled strategy and the optimization of the supply levels can make the converter output to approach the linear output as much as possible. Thus, the supply modulator can obtain the optimum efficiency. This envelope tracking (ET) transmitter was demonstrated by a GaN high efficiency PA. When driven with a 5MHz OFDM signal with 8.5dB PAPR, the supply modulator tracks the signal well. The efficiency of the supply modulator can exceed 70% and the overall efficiency of ET transmitter can be above 40% with an adjacent channel power ratio of lower than -45dBc after using digital predistortion.