High efficiency and high linearity power amplifier design

The optimum high-frequency Class-F loading conditions are inferred, accounting for the effects of actual output device behavior, and deriving useful charts for an effective design. The important role of the biasing point selection is stressed, demonstrating that it must be different from the Class-B theoretical one to get the expected improvement. The IMD behavior of the Class-F amplifier is presented and the large-signal sweet-spot origin in the IMD output characteristics is discussed, together with possible strategies to improve intermodulation distortion performances. The control of the sweet spot position is demonstrated via proper terminating impedances, both at fundamental and harmonic frequencies and low frequencies

Novel power amplifier design using non-linear microwave characterisation and measurement techniques

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

An enhanced modulated waveform measurement system

The microwave devices and circuits need to be characterized prior to being employed in the design of systems and components. Unfortunately the measurement systems required to characterize the microwave devices and circuits have not kept pace with the emerging telecommunication technologies demands. This has resulted into a situation where either the circuits being employed in the components are unoptimized or the yield and turn-around of optimized circuits are slow. One of the contributing factors of such situations is the limitations of the existing measurement systems to scale up in performance to fulfil the necessary requirements. This thesis presents an enhanced multi-tone, time domain waveform measurement and engineering system. The presented system allows for a more considered, and scientific process to be adopted in the characterisation and measurement of microwave power devices for modern day communications systems. The main contributions to the field of research come in two areas; firstly developments that allow for accurate time domain measurement of complex modulated signals using commercially available equipment; and secondly in the area of active impedance control, where significant developments were made allowing active control of impedance across a modulated bandwidth. The first research area addressed is the fundamental difficulty in sampling multi-tone waveforms, where the main achievements have been the realisation of a high quality trigger clock for the sampling oscilloscope and a “Time Domain Partitioning” approach to measure and average multi-tone waveforms on-board. This approach allows the efficient collection of high quality vectoral information for all significant distortion terms, for all bands of interest. The second area of research investigated suitable impedance control architectures to comprehensively investigate out-of-band impedance effects on the linearity performance of a device. The ultimate aim was to simultaneously present independent, baseband impedances to all the significant baseband (IF) frequency components and to 2nd harmonic that result from a multi-tone excitation. The main achievement in this area was the ability of the enhanced measurement system to present the broadband impedance. At baseband this has been achieved in the time domain using a single arbitrary waveform generator (AWG) to synthesise the necessary waveforms to allow a specific IF impedance environment to be maintained across a wide IF bandwidth. To engineer the RF out-of-band load terminations at RF frequencies and to emulate specific power amplifier modes, a Tektronix AWG7000 Arbitrary Waveform Generator was used to deliver the desired impedances, practically fulfilling the wideband application requirements for reliable device characterisation under complex modulated excitations.EThOS - Electronic Theses Online ServiceGBUnited Kingdo