宽带射频功率放大器记忆效应的研究

【作者】 何军；

【导师】 鲍景富；

【作者基本信息】 电子科技大学 ， 电路与系统， 2009， 硕士

【摘要】 随着宽带通信业务的迅猛发展和用户数量的急剧增加,现有的通信频段已经越来越拥挤。为了提高频谱利用效率,现代无线通信系统中广泛采用了非恒包络的线性调制方式和多载波技术,这对射频功率放大器的线性度提出了很高的要求。同时,为了解决功率放大器功率效率和频谱效率之间的矛盾,现在广泛采取前馈、预失真与反馈等外部线性化技术。但是实践表明,这些基本的线性化方法的实际表现总不如理论预测的那么好,这主要是由于放大器记忆效应的影响。本文主要针对宽带射频功放中的记忆效应进行理论分析及仿真,研究失真分量是如何随不同条件变化的,尤其是如何随信号的不同而变化的。主要内容如下:1.分析了射频功率放大器的主要非线性特性,阐述了放大器的几种常用模型,理论分析出这些模型不适合作为“宽带模型”。2.就宽带功率放大器中的记忆效应给出确切定义,从功率放大器的集总元件模型出发分析了电学记忆效应和热学记忆效应产生的原因,同时从高阶幅度失真的角度出发,总结出信号幅度也会引起记忆效应。3.应用Volterra模型对射频功率放大器的失真机制深入分析,获得每个非线性对IM3的影响信息,深入研究这些失真机制可以使得内部线性化成为可能。4.介绍了射频功率放大器的线性化技术及记忆效应的仿真,提出了用“归一化IM3”的指标来表征随调制频率和信号幅度变化的记忆效应,并给出了记忆效应测量的电路平台及如何校准。5.分析给出了三种有记忆效应条件下的线性化电路:阻抗优化、包络滤波、包络注入,并给出采用这些方法后的仿真结果。更多还原

【Abstract】 Since the number of users and broadband communication traffic rise rapidly, radio frequency resources are become more and more scarce. To enhance spectrum efficiency, linear modulation and multicarrier techniques are adopted widely in modern wireless communication systems, it deserves high linear radio frequency power amplifier (RF PA). Meanwhile, in order to solve the conflict between spectrum efficiency and power efficiency, external linearization techniques such as feedback、predistortion and feedforward are adopted widely. However, there are some differences between the practice results and the theory forecasts because of memory effects.The paper includes theory analysis of memory effects in the wideband RF PA and measurements, and research that the intermodulation (IM) changes with the various conditions change, especially with the various signals. The contents of the paper are as follows:1. The main nonlinear characteristics of RF power amplifiers and several basic modeling theories are described, and points out these models aren’t suitable for wideband models.2. The definition of the memory effects in RF PA are proposed, the definition of the electrical memory effects and thermal memory effects are proposed based on the SPICE modeling of the RF PA. Meanwhile, the amplitude of signal will cause memory effects by means of fifth-order analysis.3. The intermodulation mechanism are deeply analysis by means of Volterra model, and get the information that each nonlinearity contributed to IM3, it is possible for internal linearization by means of these analysis.4. Several linearization techniques and how to simulate memory effects are proposed, the figure“Normalized IM3 Components”are proposed, meanwhile, the test setup and calibration for measuring memory effects are discussed.5. Three techniques to cancel memory effects are proposed, Impedance Optimization、Envelope Filtering、Envelope Injection, then discuss their differences and simulation results are listed .更多还原