Transmisor outphasing en UHF usando amplificadores clase E a GaN HEMT
2012
A Chireix outphasing transmitter at UHF band is
presented in this paper, based on class E RF power amplifiers.
As recently proved in [1], properly transforming the load
modulation path, imposed by the non-isolated combiner, into
fundamental frequency impedan
ce 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 arch
itecture 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 measu
red, for a 11.8 W and 5.06 dB
PAPR WCDMA signal, while m
eeting ACPR specifications.
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