High Efficiency WCDMA Envelope Tracking Base-Station Amplifier Implemented with GaAs HVHBTs

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Abstract
A high-performance GaAs HVHBT WCDMA/WiMAX base-station 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 58%, with a normalized power RMS error of 2.9% and ACLR1 of -49 dBc with digital predistortion (DPD), at an average output power of 42 W and gain of 10.2 dB for a single carrier WCDMA signal at 6.6 dB PAR. To the authors' knowledge, this corresponds to the best efficiency reported for a single stage WCDMA base-station power amplifier. For 7.7 dB PAR single carrier WCDMA overall PAE reached 55%, with a normalized power RMS error of 2.9% and ACLR1 of -48 dBc with DPD, at an average output power of 33 W and gain of 10.2 dB. 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. DPD with memory mitigation resulted in -70 dBc ACLR1&2 and 0.3% RMS error, resulting in a best reported linearization improvement result. For 10 MHz WiMAX at 8.8 dB PAR overall PAE reached 48%, with an ACLR1 of -41 dBc with DPD, at an average output power of 25 W and gain of 10.4 dB.

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