Seguimiento de la envolvente con ganancia constante mediante esquema outphasing en tecnología GaN HEMT

Abstract

A UHF outphasing transmitter, based on parallel-circuit Class E power amplifiers (PAs) and implementing a constant-gain envelope tracking strategy, is presented in this paper. Using the nonlinear model of the selected GaN HEMT device, the drain terminating and biasing networks are designed to provide near optima impedance values at the fundamental and higher order harmonics. A relatively wideband performance, 630-890 MHz, is obtained with an efficiency above 80%, besides being amenable for load-modulation. Thanks to the use of a series Chireix combiner, followed by an impedance transformer, an outphasing scheme is implemented. Once characterized in a pure output power phase-coding regime, the observed limitation in dynamic range is overcome by operating the amplifiers in a sort of continuous class J mode, while introducing a constant gain load envelope tracking strategy. A 1c-WCDMA signal, with a peak-to-average power ratio of 8.4 dB is shown to be reproduced, satisfying the linearity requirements, with an average power efficiency of 58%.