Transmisor outphasing en UHF usando amplificadores clase E a GaN HEMT

Abstract

A Chireix outphasing transmitter at UHF band is presented in this paper, based on class E RF power amplifiers. As recently proved, properly transforming the load modulation path, imposed by the non-isolated combiner, into fundamental frequency impedance values at the device drain terminals as close as possible to those assuring zero voltage switching condition, good efficiency values may be kept along a significant output power range. A lumped element implementation of the amplifiers and the combiner, together with the use of GaN HEMTs, allowed controlling the output power over a 6 dB range with an efficiency value over 60%. Experiments with asymmetrical two tones, conceived as a discrete spectrum signal with a 1:4 envelope variation, have shown the capability of the architecture to be linearized using digital predistortion (DPD). In order to reproduce a spectrally efficient communication signal, with nulls in the envelope, a hybrid control strategy was employed, combining the outphasing between branches with amplitude variations of both RF excitation signals for the lower range of the envelope. Average drain efficiency and PAE values of 63% and 60.3% respectively have been measured, for a 11.8 W and 5.06 dB PAPR WCDMA signal, while meeting ACPR specifications.