Abstract:
The increase in demand of wireless devices has put a greater importance on the RF front–end
components. In particular, the power amplifier (PA) is the main power consuming component
in any transmitter of wireless device. Therefore, improving the efficiency of the power
amplifier is crucial to extend battery lifetime (e.g. on a satellite or on a mobile base station)
and reduce power loss. This in turn has significant effects on the total cost of the transmitter.
Rapid growth of communication standards has prompted the development of broadband PAs.
These are useful in the context of backward compatibility of communication systems. These in
turn reduce the deployment cost of large scale base transceivers stations with rapid changes in
the wireless standards. They can be compatible with the upcoming as well as existing standards.
Moreover, such PAs fin utility in software defined radio platform where a broadband front-end
is required to provide a multi standard feature to the radio.
GaN technology has recently been growing in prominence due its high voltage capability.
Development in laboratories and various device manufacturers has spurred the demand for
accurate nonlinear models. The development of a large signal transistor model for a pHEMT
based on simplified Angelov Model is reported. Nonlinear embedding technique is also
presented which has a distinct advantage over the conventional load pull analysis.
The thesis also discusses Class-F mode of operation with the design of a high efficiency power
amplifier working at 2 GHz. This is followed by broadband high efficiency PAs operating in
continuous class-B/J mode of operation. A novel approach for engineering the extrinsic
harmonic impedance which can be realizable using a passive foster circuit is proposed. This
resulted in a power amplifier working between 1.3 GHz and 2.4 GHz with state-of-the-art
performance. Both the designs were based on the nonlinear-embedded model. After using
passive components to match the amplifier output, an investigation into matching the output
using active circuit was also carried out. Second harmonic signal was injected externally using
a frequency doubler to properly shape the waveforms at the drain. Preliminary results are
encouraging and promising. This architecture leads to an improvement in both drain efficiency
and fundamental output power across a band of 1.3-2.4 GHz.
