RF Power Amplifier Linearization Technique

Modern communication systems tend to use a linear modulation scheme, which is the pursuit of higher spectral efficiency and data rate. These linear modulation technique has the following characteristics, First:non-constant envelope; Second:wideband; third:the Peak-to-Average Power Ratio is relatively high. RF system needs to have excellent linearity characteristics in order to meet the requirements of these linear modulation, and linear characteristics of modern communication systems are mainly affected by the power amplifier linearity, so the field of wireless communications at home and abroad, the output amplifier linearization is an important issue in the wireless communication, this is also a focus of research in recent years. Some new power amplifier linearization techniques have emerged as people study ratio frequency power amplifier (RFPA) linearization techniques in-depth, such as:adaptive feedforward technology, loops feedback technology, digital predistortion technology, adaptive predistortion based on integration of multi-formulas technology, CALLUM (Combined Analogue locked Loop Universal Modulator) technology, LINC(Linear amplification using Nonlinear Components) technology. Because some of Feedforward technology’s advantages, such as can improve the linearity better, the system is unconditionally stable, high reliability, Feedforward technology become the focus of this thesis.The main contents of this paper are:1:Introduced the amplifier model, some nonlinear characteristics of amplifier are discussed, such as harmonic distortion, intermodulation distortion, AM-AM effect and AM-PM effect. Analyze the characteristics of AM-AM effect and AM-PM effect, provides a theoretical basis for power amplifier linearization compensation.2:Based on the exact definition of the memory effect, analyzed the cause of the memory effect’s generation, discussion several important factors affecting the memory effect provides a theoretical basis to reduce memory effect.3:Expounded the basic principle such as feedback, LINC and CALLUM linearization techniques, analyze feedforward’s working principle, elaborated feedforward gain of the system and system features.4:set up the feedforward amplifier system, use the ADS (Advanced Design System) simulation software to simulate feedforward system, simulation results show that the analysis of feedforward system in the fourth chapter is correct, the simulation results also show that the feedforward technique can improve the nonlinear characteristics of amplifier well. Finally, the development trend and the advantages and disadvantages of feedforward technology are summarized.