Efficient and Wideband Power Amplifiers for Wireless Communications
The rapid evolution of wireless communication systems and the development
of new standards require that wireless transmitters process several types of
standards across multiple bands. Power amplifiers (PAs) are key components
in wireless transmitters because they have a big impact on the overall system
performance in terms of their bandwidth, efficiency, and linearity. This thesis
presents various design techniques that improve bandwidth and efficiency
characteristics of the PA.
For narrowband transmitters, a circuit design methodology that enables
first-pass design of high efficiency single-ended PAs is presented. The method,
based on employing bare-die transistors, specialized modeling technique, and
optimization of harmonic impedances, is validated with excellent experimental
results. A class-F−1 PA at 3.5GHz and a harmonically tuned PA at 5.5GHz
are designed and implemented demonstrating 78% and 70% PAE respectively.
For broadband transmitters, a design methodology for single-ended PAs
with octave bandwidth is presented and verified. The method is based on a
harmonic tuning approach combined with a systematic design of broadband
matching networks. The demonstrator PA achieves 50-63% PAE across 1.9-
4.3GHz. Then, extending the bandwidth beyond one octave while maintaining
high efficiency is investigated by adopting a push-pull configuration. For this
reason, a novel push-pull harmonic load-pull measurement setup is proposed
and a push-pull PA operating between 1-3GHz is implemented. The investigation
demonstrates the proposed setup as an important tool for understanding
and optimizing PAs and baluns for wideband push-pull microwave PAs.
For multi-band transmitters, using signals with large peak-to-average power
ratio, the design of dual-band Doherty PAs (DPAs) is considered. A detailed
analysis of each passive structure constituting the DPA is given, leading to
different configurations to implement dual-band DPAs. One of the configurations
is implemented, leading to state-of-the-art results for dual-band DPAs.
Finally, the multi-band branch-line coupler (BLC) is a key component for also
extending the design of DPAs to multi-band in the future. A closed form
design approach for multi-band BLCs operating at arbitrary frequencies is
presented and validated by the successful design of dual-band, triple-band,
and quad-band BLCs.
The excellent results obtained demonstrate the success of the developed
design methodologies for high efficiency and multi-band/wideband PAs. These
methods will contribute to the design of future wireless systems with improved
performance in terms of efficiency, bandwidth and hence cost.
Doherty power amplifier
Kollektorn, Kemivägen 9, Chalmers University of Technology
Opponent: Associate Professor Slim Boumaiza, Department of Electrical and Computer Engineering, University of Waterloo, Canada