Design And Implementation Of The Control System For The Adaptive Feedforward Amplifier

The modern communication technique has been transformed from transmitting voice and words to the service of multimedia and Internet access. The transition demands a much higher data rate on communication system. In order to maximize data throughput, as well as enhancing spectral efficiency, more complex non-constant envelope modulation techniques are commonly employed in modern communication systems. While these modulated signals generally have higher peak-to-average power ratio, which would substantially decrease the efficiency of a power amplifier so it’s necessary to introduce linearization techniques to compensate for the linearity.The feedforward amplifier possesses many benefits, such as wide bandwidth and excellent linearity, so it’s applicable to be implemented in modern communication system. While the feedforward amplifier is an open-loop, so it requires an accurate gain and phase adjusting to be maintained on various components, then the correction could be obtained over temperature and the aging of different elements. Various kinds of adaptive control methods are viable. So designers should select appropriate scheme according to the design requirement. To obtain the optimum performance, the adaptive control algorithm should also be modified on the basis of the capability of hardware. The thesis describes the design of a linearization technique that used spread-spectrum signal as pilot signal. The research, based on previous studies, has made improvements.The first chapter of the thesis introduces the research background and the necessity of the research. The second chapter elaborates the linear and non-linear characteristics of power amplifiers, and introduces several parameters, such as 1d B Compression Point and 3 order Intercept Point, to measure the linearity of the power amplifier. The third chapter introduces several commonly used linearization techniques for power amplifier, and analyzes their respective pros and cons. The fourth chapter introduces the design of adaptive feedforward amplifier, including direct detection and pilot-assisted detection. The fifth chapter introduces the design and implementation of the digital controller for feedforward amplifier. The sixth chapter shows the test results, and proposes feasible modifications for the design.