Research And Design Of High Efficiency Power Amplifier

RF power amplifier is the most important device in the front end of base station transmission.It is closely related to wireless communication systems.With the development of technology,the modulation signal has the characteristics of high average peak ratio,and the signal bandwidth will increase.With the emergence of the Fifth Generation(5G)communication technology,higher requirements are put forward for the bandwidth of power amplifier.On the other hand,power amplifier is the main energy consuming device in the system,and with the increasing number of communication equipment,the problem of energy consumption is becoming more and more serious.High efficiency power amplifier is able to alleviate this problem.Therefore,the research of high efficiency and wideband power amplifier has become a hot spot and focus.Therefore,this dissertation mainly aims to research and design a wideband power amplifier with high efficiency.This dissertation first analyzes the research progress of Doherty power amplifier at home and abroad in recent years,and analyzes and summarizes the research results of broadband design based on Doherty structure and high efficiency or high regression design based on Doherty structure.Then the design index and key technology of power amplifier are introduced,and the amplifiers with symmetrical Doherty structure and asymmetric Doherty structure are analyzed in detail,and the advantages and disadvantages of the two type of amplifiers are summarized.Secondly,based on the above research background and direction,in order to improve the efficiency of Doherty structure power amplifier,this paper designs a power amplifier based on asymmetric Doherty structure.The asymmetric Doherty structure is better than Doherty structure in the regression-efficiency of power amplifier.In this dissertation,the single-pipe main power amplifier is designed.At the same time,in order to ensure that the design of asymmetric Doherty power amplifier meets the performance,the main circuit power amplifier is made plate,debugged and measured.The test results also provide reference measured data for the subsequent proof of the efficiency of asymmetric Doherty structure.The test results of a single power amplifier show that the saturated output power at the frequency point of 3.5GHz is 46.02d Bm,the saturated drain efficiency is 74%,and the drain efficiency at the power back-off 8d B is 37%.Then,this paper completes the overall circuit design,simulation,production and testing of asymmetric Doherty.The test results of asymmetric Doherty power amplifier show that the saturated output power can be 47.02d Bm,the saturated drain efficiency can be 73.5%,and the drain efficiency at 8d B power back-off point is greater than 47.5%^[60].Compared with the drain efficiency of the single tube,it can be seen that the power amplifier back-off efficiency of the asymmetric Doherty structure is much higher than that of the single tube,and maintains high efficiency in the back-off zone.Each index of the asymmetric Doherty power amplifier meets the expected design requirements.Finally,in order to widen the working bandwidth of the asymmetric Doherty power amplifier,the bandwidth limiting factors of the asymmetric Doherty structure are analyzed in detail,and the reasons for the quarter-wavelength transmission line to limit the bandwidth of the power amplifier are further analyzed.Aiming at this limitation factor,a wide-band asymmetric Doherty power amplifier was redesigned by changing the output load impedance and removing the quarter-wavelength transmission line after the junction point.The asymmetric Doherty structure was improved.The simulation results show that the drain efficiency is 64.8?73.2%,the saturated gain is 10.5?11.5 d B,the gain flatness is good,the saturated output power is maintained in 46.5?49 d Bm,and the working bandwidth is expanded by 50%in the bandwidth of 3.3?3.7GHz.