| With the rapid development of modern wireless communication systems,especially for popularized LTE communication system nowadays, the design of poweramplifiers for high efficiency has become a challenging task due to increasinglystringent requirements placed upon transmitters using spectrum efficient modulationtechniques, so the research of high efficiency power amplifier (HEPA) is become moreand more urgent. This thesis aims at how to improve the efficiency of power amplifier,through researching Doherty amplifier, and then puts to use a new structure to furtherimprove the efficiency of Doherty power amplifier. The major operations are listed asfollows:1. This thesis analysis the important of HEPA, and comparative analysis somehigh efficient technology of power amplifier that are being studied nowadays. And thendiscusses the historical aspects, research status and modern trends of Doherty poweramplifier.2. The active load-pull theory is used to research and analyze the Doherty poweramplifier theory in terms of the impedance and efficiency. Next, this thesis states theDoherty amplifier techniques covers symmetrical structure, Asymmetrical structure andmultistage structure on this base. The final section of this chapter analyzes the actualDoherty Power amplifier design key points, in Particular, the offset line has beendetailed analyze.3. According to design specifications requirement of power amplifier for LTEsystem, with the help of ADS and HFSS simulation tools, the3-dB coupler, singlepower amplifier and classical Doherty power amplifier are different simulated, and theresults of the simulation are meet requirement.4. Based on the analysis and simulation of the influence between the power ratioand the efficiency, this thesis proposes a novel input power splitter that canautomatically adjust the input power ratio in accordance with the lager of input powerlevel. The simulation results show that the efficiency of modified Doherty poweramplifier has an improvement of about4%at the power back-off point from saturation, and the linearity has not worse.5. Finally, all of artificial circuits are processed and tested, especially for theDoherty power amplifier. It turn out that the modified Doherty power amplifier has46.5%efficiency at the power back-off6dB from saturation, which is more than2%improvement compared with the classical Doherty power amplifier, and the testingresults of IMD3for linearity were similar. |
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