Research On The Predistortion Radio Frequency Power Amplifier

The information transmission technology of modern communicationsystem is developing rapidly in direction of multi-carrier, multi-level,broadband and high Peak-Average-Ratio (PAR). New broadband digitaltransmission techniques (such as OFDM, MC-CDMA and WCDMA) andhigh spectrum efficiency modulation techniques (such as QPSK andM-QAM) are extensive used. These high efficient multi-carrier &multi-channel digital modulation transmission techniques, which arebased on non-constant envelope, request high linearity of radio frequencypower amplifiers (RFPAs). When signal is amplified by RFPAs,intermodulation distortion is generated, which results in spectral regrowth,then leads to adjacent channel interference. In modern wirelesscommunication system, adjacent channel interference has got stringentrestrictions, for instance, according to 3GPP WCDMA specification, ifthe adjacent channel power is greater than-50dBm then the AdjacentChannel Power Ratio (ACPR) shall be higher than the value of33dBc@5MHz and 43dBc@10MHz. Furthermore, power amplifier alsoneed give attention to high efficiency in wireless communication system,the linearization technique for RFPAs is neccessary.The research include electrical memory effects and thermal memoryeffects of RFPAs, adaptive RF predistortion system and design ofpredistortion RFPAs etc.. Following four aspects are originalityinnovation discoveries:1．Researched, modeled and simulated electrical memory effects ofRFPAs, analyzed how it affect the performance of RFPAs,pointed out that electrical memory effects are caused by thevariation of in-band impedance, also baseband impedance affectselectrical memory effects much more than RF impedance. These results provided theory basis for decrease electrical memoryeffects successfully. Impedance design method to minimize theelectrical memory effects of RFPAs was presented and used inthe design of real RFPAs .2．Researched, modeled and simulated thermal memory effects ofRFPAs, analyzed how it affect the performance of RFPAs,pointed out that thermal memory effects is caused by the thermalsensitivity of active power components. Several design mothodsof to minimize the thermal memory effects RFPAs was presentedand used in practice.3．Gave an overview of adaptive algorithm used in adaptivelinearization techniques, categorized them and introducedconditions and the relationship among them. A high efficiencyadaptive optimum algorithm applicable for predistortionRFPAs was presented. The main idea of this algorithm is that theout-of-band intermodulation distortion of the output of RFPAswas abstracted to be the optimizing goal, it was minimized byoptimizing the predistortion coefficients, which was abstractedby the multi-directional search algorithm with globle stableconvergency. According to simulation results, adaptive rate ofconvergency increased obviously comparing to traditionaladaptive optimum algorithm, and out-of-band intermodulationdistortion was improved by 15dB .4．Based on adaptive predistortion theory, a design scheme ofpredistortion RF PAs was presented and implemented. Someaparts have been fabricated. The performance of thispredistortion system will be verified.