Research Of The Linearization Of The Power Amplifier

In recent years, the demand of wireless communication business has increasedsharply, makes the communication frequency band more and more crowded. Thatpromotes researchers to search the linear modulation technology which has higherfrequency utilization. As a result, the QPSK, QAM and other Non-constant envelopemodulation technology get great development gradually. Differ from the constantenvelope modulation technique like GSMK, they have high PAR(Peak to AverageRatio).The enormous fluctuation in amplitude has great affects on the linearity of theRF amplifier and will decrease the communication quality. Therefore,enhancing thelinearity of the amplifier is the main way to achieve better transmission quality. Somore and more communication equipment companies, research institute and collegesbegin to pay attention to the PA’s linearity now.This paper briefly introduces the property of the RF amplifier and the theory ofthe non-linearity of PA. Mainly introduce the theory, advantages and shortcomings ofseveral linearization techniques such as feedforward, feedback, LINC, EE&R,Pre-distortion. Describes the derivation of the No-memory amplifier models likeSaleh model, Taylor model, Rapp model and the memory effect model like Voterramodel, Viener model, Hammerstein model. Based on the complex gain mode, use thesoftware ADS to complete the digital pre-distortion simulation, verifying thelinearization effect from the principle view. Data demonstrates that it can improve theIMD326dB under the test conditions of two tone500KHz spacing.Finally, According to the requests of the military radio station,Participate in thedesign of the225MHz-512MHz wideband amplifier. Amplifier consists of two parts,the first stage uses the Freescale MOSFET MW6S010and made a large power backoff to achieve high linearity. The main stage uses the NXP LDMOS transistorBLF645.A lot of simulation，optimization and test were carried out during the design.Besides, for the225MHz-512MHz broadband amplifier in project, use thenumerically controlled analogy pre-distortion to perfect the linearity in every10MHz.According to the data tested, under the circumstance of20W output, two tonewith100KHz spacing,the IMD3improves4-10dB，above-35dBc，the highest up to -44dBc,and the efficiency reaches above33%.The other index like gain flatness,harmonic suppression achieve the expected requirements.