بررسي و طراحي يك تقويت كننده ي توان راديويي خطي با استفاده از روش پيش اعوجاج

چكيده انگليسي :

Analysis and Design of a Linear RF Power Amplifier Using Predistortion Technique Marzieh Saffari Khoozani m saffarikhoozani@ec iut ac ir Date of Submission 2011 4 17 Department of Electrical and Computer Engineering Isfahan University of Technology Isfahan 84156 83111 Iran Degree M Sc Language Persian Supervisor Rasoul Dehghani dehghani@cc iut ac irAbstractNowadays with rapid growth of wireless communication systems demand for integration of wirelesstransceivers on a single chip called system on chip SoC has been increased Therefore CMOS technologyis widely used to implement SOCs because of its low cost and high capability of integration RF poweramplifier is one of the most important components in a communication system Nowadays most of newdigital communication standards such as WiMAX rely on modulations like OFDM because of their highspectral efficiency The main disadvantage of OFDM is its high peak to average power ratio which makes itvery sensitive to nonlinearity of power amplifier The nonlinearity of a power amplifier gives rise to spectralregrowth magnitude and phase distortion in the transmitted signal Most high efficiency power amplifiers areintensively nonlinear and therefore cannot be used for OFDM signal amplification On the other hand tohave a high efficiency power amplifier in any portable communication system is very important in the powerconsumption point of view One method to amplify signals like OFDM by nonlinear power amplifier is toapply some linearization techniques on power amplifier to improve its nonlinear behavior Among differentlinearization techniques predistortion is one of the most popular techniques that can be realized by usingproper digital structures Among different ways for implementing predistorter look up table orimplementation by modeling power amplifier implementation of predistorter by modeling power amplifieris more proper way of implementation because in look up table implementation we need a large amount ofmemory for saving correction coefficients and convergence speed for updating of these coefficients is veryslow Also this approach is not appropriate for applications that deal with wideband modulation This isbecause in such applications power amplifier memory effect due to frequency dependence of impedances cannot be disregarded In this thesis adaptive memory polynomial based predistorter is used to linearize thepower amplifier Memory polynomial is an accurate and simple model for modeling nonlinear systems withmemory The coefficients of predistorter are extracted using indirect learning structure based on an adaptivealgorithm like LMS or RLS The main advantage of this approach is that it can work with any nonlinearcharacteristics of power amplifier in an adaptive manner The aim of this thesis is to evaluate theperformance of this technique for linearizing CMOS power amplifiers We use this technique to linearize aCMOS power amplifier with a paralleled class A and AB structure In the performed simulations somepractical limitations such as fixed point calculations for predistorter and limited resolution for ADC areconsidered Simulation results demonstrate noticeable improvement in in band and out band distortion in theoutput signal of power amplifier with 18 1dBm output power and 26 8 efficiency ACPR and EVM areimproved by 8 6dB and 7 7dB respectively while the output signal meets the spectral mask requirement ofWiMAX standard including predistorter In addition it has been shown that RLS algorithm is more properthan LMS algorithm to extract predistorter coefficients due to its high accuracy and speed Finally the resultsobtained from a sample digital predistorter synthesized on Spartan3 xc3s4000l FPGA presented Key Words RF power amplifier Power added efficiency PAE OFDM Adaptive memory Polynomial based predistorter Memory effect

صفاري خوزاني، مرضيه

بررسي و طراحي يك تقويت كننده ي توان راديويي خطي با استفاده از روش پيش اعوجاج

بازده افزوده ي توان , OFDM , اثر حافظه