Research On Linearization Technologies For Radio Frequency Power Amplifier

With the rapid development of wireless communication, in order to make more efficient use of frequency spectrum and achieve greater power efficiency, the linear modulation methods and high-efficiency Radio Frequency power amplifiers are widely used. Since the envelope of modulated signal fluctuates, unwanted intermodulation distortions generated when the signal is amplified by the nonlinear RF power amplifiers. The intermodulation distortions will lead to severely inter-symbol interference and adjacent channel interference. The high linear power amplifier has to be used to guarantee communication quality. Unfortunately, power efficient amplifiers are typically nonlinear. For solving this problem, various linearization techniques have been employed to improve the linearity of high efficiency power amplifier.In this thesis, the non-linear characteristics of power amplifier are analyzed in theory at first. The principle, advantages and disadvantages of various linearization techniques are discussed. Then, detailed theory analysis and CAD simulations are carried on for RF predistortion linearization and feedforward linearization, because these two kinds of linearization techniques are most important and have greater practical application value. At the end of this thesis, two types of RF predistortion linear power amplifier circuits have been fabricated. The experimental results are in good agreement with theoretical analysis. It indicates the two types of RF predistortion linear power amplifiers have the advantages in the applications of satellite communication system and mobile communication system. The contributions of the thesis are presented as follows:1. A RF quadrature power series predistortion linearizer is presented. This technique can efficaciously correct for both amplitude and phase distortion of power amplifiers.2. Individually controlled by look-up table and adjacent channel power minimization, two kinds of adaptive predistortion linearizer are formed and simulated with computer. Simulating results show that adaptive control technologies can efficaciously extend dynamic range of linear power amplifiers3. A novel series FET predistorter is developed by utilizing the gate-voltage controlled variable resistance characteristic of FET. Unlike common predistorters that have great insert loss, this technology can offer some power gain whilelinearize the amplifier without additional components.4. Under the condition of loop imbalance in feedforward linearization system, investigations are made on the effects of the further nonlinear distortion produced by auxiliary amplifier on the overall linear performance. The system perfomance is presented as a function of circuit parameters, phase and amplitude imbalance.5. Critical conditions for reducing the power level of auxiliary amplifier are presented. For given circuit parameters and requirement of system performance, the minimum power level of auxiliary amplifier can be validly predicted. It can improve the power efficiency and minimize the cost of feedforward linearization system.6. An adaptive predistorting linear amplifier based on look-up table method is fabricated. The results of measurement show that the technology can great improve the linearity of amplifier. This circuit is valuable in practice.7. A series FET predistortion linearizer circuit is constructed. Experiment results are in good agreement with theoretical analysis, so it can be wildly used in satellite communication system and mobile communication system.