Abstract:
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A UHF outphasing transmitter, based on parallelcircuit
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 sort of ISOGAIN 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%. |