Three-band high-efficiency modulator for envelope tracking power amplifier using class-B push-pull amplifiers

Envelope modulators for wideband and high- power envelope tracking or envelope elimination and restoration amplifiers are usually realized by combing a switching stage and a linear stage. The efficiency and bandwidth of the modulator is mainly limited by the linear stage. This paper proposes a method to improve the performance of the linear stage by adding another stage. The third stage is a push-pull amplifier biased in class-B mode. The push-pull amplifier can achieve a peak efficiency of 76%, and well above 60% over the envelope frequencies from 1MHz to 20MHz. By adding this push-pull amplifier, the three-band modulator can achieve a peak efficiency of 81% and an effective efficiency of 73% for 10MHz and 20MHz LTE signals with 30W output power. The linearity of the push-pull amplifier and the three-band modulator has been evaluated. The three-band modulator has also been tested by driving a class-E amplifier at 2.06GHz to validate the design.