| Today's society is in a period of increasingly developed wireless communications,as the core component of communication system,RF(Radio Frequency)power amplifier module is increasingly leading the research trend,and Doherty power amplifier circuit used in base station is becoming a field of exploration for many scholars.In this thesis,a large number of relevant references are reviewed,and the development history and future trend of the Doherty power amplifier is discussed.On this basis,the research results and development dynamics of broadband and high efficiency Doherty power amplifier in domestic and overseas are summarized.This thesis first introduces the related theory and key technologies of Doherty power amplifier in base station,then the efficiency and bandwidth of Doherty power amplifier based on Ga N transistor is studied.The main work and innovation contribution are as follows:Firstly,the bandwidth limiting factor of Doherty power amplifier is studied.Then a modified load modulation network is proposed.its aimed at the effect of impedance transformation line on the working frequency band of Doherty combinational structure.The load modulation network mainly combines the parallel combination structure and parallel 1/4 wavelength shorting line.Finally,based on this,a Doherty power amplifier circuit with frequency coverage of 1.6-2.6GHz is designed for wireless communication system,The measured saturation power is higher than 41 d Bm and the drain efficiency(DE)is above 35% with 6d B power back-off,and linearized adjacent channel power ratio(ACPR)is better than-45 d Bc.Secondly,the reason of Doherty power amplifier circuit back-off efficiency is explored.As we all know,The output impedance of a carrier semiconductor in Doherty power amplifier is closely related to its efficiency,failing to achieve optimal output impedance severely limit the efficiency of Doherty amplifier power back-off.In view of the above defects,an idea of optimal load impedance matching is proposed based on the previous research.A Doerty amplifier circuit with high efficiency is designed based on this idea.The physical test is implemented in the band of1.6-2.6GHz 6d B fallback efficiency above 41.5% and saturation efficiency equally above 50.8%.Finally,Doherty power amplifier circuit mode of operation is analyzed.This thesis consideres the problem of unbalanced drain current caused by two branches of Doherty power amplifier in different bias states,then proposes a novel asymmetrical structure.Also,two typical different power semiconductors is selected in this circuit design.The high back-off performance is focused,and defects such as lower drain output current of the peak branch are compensated.The measured frequency band is 1.6-2.2GHz,and the saturated output power better than 44.4d Bm and the 6d B power back-off efficiency higher than 42% are obtained in the measured bandwidth.The mostimportant is that the 9d B power back-off efficiency of the power amplifier circuit is also above36.5%.In summary,this thesis has developed a variety of Doherty power amplifier with application value.These Doherty power amplifier are mainly designed for working bandwidth and back-off efficiency,and are intended to meet the peak-to-average ratio of the signal in the wireless communication system and the bandwidth requirement of the carrier aggregation technology.Finally achieves both the purpose of high back-off efficiency and the progress of working bandwidth,which provides an important technical reference for the research and design of the power amplifier in the future mobile communication system. |
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