Envelope Tracking Supply Modulator with Trellis-Search-Based Switching and 160-MHz Capability

Abstract

The hybrid amplifier that combines a buck converter and a linear amplifier has been widely used as the envelope tracking (ET) supply modulator for ET power amplifier (PA) application. Instead of adding more large off-chip passives to raise the efficiency of the hybrid amplifier, this work uses a Viterbi-like trellis search (TS) digital signal processing (DSP) algorithm to find the optimal switching sequence for the buck converter in the hybrid amplifier, lowering RMS error current in the op-amp, and minimizing switching. For 20-MHz channels, it lowers op-amp current by 27%. The chip also supports 160-MHz channels without TS. With 802.11ax modulation, it raises total efficiency of a 2.5-GHz PA by 7.2% at 22.3 dBm, with EVM of −32.7 dB.