50% PAE WCDMA basestation amplifier implemented with GaN HFETs

A high performance GaN HFET WCDMA basestation power amplifier is presented, which uses an envelope tracking bias system to achieve high linearity and efficiency. The measured overall power-added efficiency (PAE) reached 50.7%, with a normalized power RMS error of 0.7% and ACLR of -52dBc at an offset frequency of 5MHz, at an average output power of 37.2W and gain of 10.0dB for a single carrier WCDMA signal. To the authors' knowledge, this corresponds to the best efficiency reported for a single stage base station power amplifier. Digital predistortion (DPD) was used at two levels: memoryless DPD to compensate for the expected gain variation of the amplifier over the bias envelope trajectory, and deterministic memory mitigation, to further improve the linearity. The signal envelope had a peak-to-average power ratio of 7.67dB.