A UHF outphasing transmitter based on class E power amplifiers

In this paper, an outphasing transmitter operating at UHF band (770 MHz) is presented, based on highly efficient Class E RF power amplifiers (PAs). Implemented on GaN HEMT technology and following a load modulation path close to the optimum, a simple lumped-element Chireix combiner allows obtaining an efficiency value over 60% along a 7 dB output power range. Spectrally efficient digital modulation formats, with nulls in the envelope, may be handled by means of a hybrid technique, combining outphasing modulation with envelope variation of the RF excitations. Average drain efficiency and PAE values of 68.6% and 66.2%, respectively, have been measured, for a 14 W WCDMA signal with a 5.06 dB PAPR, while meeting ACPR specifications.