Wideband high efficiency digitally-assisted envelope amplifier with dual switching stages for radio base-station envelope tracking power amplifiers

This paper presents a novel envelope amplifier architecture to improve the overall efficiency of wideband high linearity envelope tracking power amplifiers (PAs). We show here a technique to increase the efficiency of the envelope amplifier while maintaining the amplifier's bandwidth. The technique utilizes digital signal processing (DSP) control in conjunction with analog hysteretic feedback. Two high efficiency buck switching stages are coordinated to provide the wideband envelope power to the RF stage; a wide bandwidth linear regulator is also used at low power to maintain the envelope signal accuracy. The technique improves the efficiency of the envelope amplifier, especially for applications requiring high peak-to-average power ratio (PAPR) with wide bandwidth signals. The overall system was demonstrated using a GaAs high voltage HBT PA. For a variety of signals ranging from 6.6dB to 9.6dB PAR and up to 10MHz bandwidth, the overall system PAE reached above 50%, with a normalized power RMS error below 5% and ACLR1 of -50dBc with memory-less digital predistortion, at an average output power above 19W and gain of 10dB. The efficiencies obtained are the best ever reported, to our knowledge, for envelope tracking base station amplifiers for these signals.