Novel power amplifier design using non-linear microwave characterisation and measurement techniques
Ogboi, Friday Lawrence
This thesis, addresses some aspects of the well-known, problem, experienced by designer of\ud radio frequency power amplifiers (RFPA): the efficiency/linearity trade-off. The thesis is\ud focused on finding and documenting solution to linearity problem than can be used to\ud advance the performance of radio frequency (RF) and microwave systems used by the\ud wireless communication industry. The research work, this was undertaken by performing a\ud detailed investigation of the behaviour of transistors, under complex modulation, when\ud subjected to time varying baseband signals at their output terminal: This is what in this thesis\ud will be referred to as “baseband injection”. To undertake this study a new approach to the\ud characterisation of non-linear devices (NLD) in the radio frequency (RF) region, such as\ud transistors, designated as device-under-test (DUT), subjected to time varying baseband\ud signals at its output terminal, was implemented. The study was focused on transistors that are\ud used in implementing RF power amplifiers (RFPA) for base station applications. The nonlinear\ud device under test (NL-DUT) is a generalisation to include transistors and other nonlinear\ud devices under test. Throughout this thesis, transistors will be referred to as ‘device’ or\ud ‘radio frequency power amplifier (RFPA) device’. During baseband injection investigations\ud the device is perturbed by multi-tone modulated RF signals of different complexities. The\ud wireless communication industry is very familiar with these kinds of devices and signals.\ud Also familiar to the industry are the effects that arise when these kind of signal perturb these\ud devices, such as inter-modulation distortion and linearity, power consumption/dissipation and\ud efficiency, spectral re-growth and spectral efficiency, memory effects and trapping effects.\ud While the concept of using baseband injection to linearize RFPAs is not new the\ud mathematical framework introduced and applied in this work is novel. This novel approach\ud NOVEL POWER AMPLIFIER DESIGN USING NON-LINEAR MICROWAVE CHARACTERISATION AND MEASUREMENT TECHNIQUES CARDIFF UNIVERISTY - UK\ud ABSTRACT vi\ud has provided new insight to this very complex problem and highlighted solutions to how it\ud could be a usable technique in practical amplifiers.\ud In this thesis a very rigorous and complex investigative mathematical and measurement\ud analysis on RFPA response to applied complex stimulus in a special domain called the\ud envelope domain was conducted. A novel generic formulation that can ‘engineer’ signal\ud waveforms by using special control keys with which to provide solution to some of the\ud problems highlighted above is presented.\ud The formulation is based on specific background principles, identified from the result of both\ud mathematical theoretical analysis and detailed experimental device characterisation.