| Radio frequency power amplifiers are the most important part of transmitters.To deal with high peak-to-average ratio signals of the fifth generation(5G)communication system,power amplifiers must have high back-off efficiency and meet the requirement of broad bandwidth.Doherty power amplifiers are effective efficiency enhancement technique that can maintain high efficiency in the output power back-off range.However,the conventional architecture of Doherty power amplifiers leads to its own narrowband characteristics,which is difficult to meet the requirement of broadband.Therefore,the research of broadband Doherty power amplifiers is of great significance to the application and development of 5G communication system.This thesis researched and designed the conventional Doherty power amplifier firstly and the wideband bias circuit,matching circuit and power synthesis circuit were further studied to expand the working bandwidth of the whole Doherty power amplifier.The main work and innovations are as follows:(1)The 2.11-2.17 GHz Doherty power amplifier was designed based on the conventional Doherty power amplifier architecture.Firstly,the simulation design and actual test of class AB power amplifier were carried out.The saturation output power at 2.11 GHz,2.14 GHz and 2.17 GHz is 45.4 d Bm,45.3 d Bm and 45.7 d Bm,respectively,and the corresponding drain efficiency is 42%,43% and 44%.Then the whole Doherty power amplifier was designed and tested based on the optimized class AB power amplifier.The test results show the maximum output powers of Doherty power amplifier are more than 48 d Bm.The efficiencies at saturation and 6 d B power back-off are 43.3-51.5% and more than 30%.(2)Aiming at the wideband of output matching circuit,bias circuit and power synthesis circuit,a wideband design scheme was proposed to improve the traditional Doherty power amplifier architecture.Double impedance matching method was used to design the output matching circuit of the main power amplifier to ensure good matching in the back-off and saturation conditions.Combined with post-matching method,the power synthesis network was designed to replace the quarter wavelength microstrip line in the traditional architecture and ensure the improvement of bandwidth.The bias circuit used microstrip radial stub and microstrip line to realize the high impedance for radio frequency signals in the wide band and the simulation and measurement results show the design is effective.(3)According to the proposed design scheme,a 3.3-3.7 GHz broadband Doherty power amplifier suitable for 5G band was designed.The debugging circuit of power divider was designed and applied to the overall layout design.Each module of the real object produced by the layout can be debuggable and tested separately,which reduced the difficulty of debugging and testing.In addition,Ga N power sequence circuit was designed to prevent the transistor from being damaged by power sequence errors.The actual test results show that in the working range of 3.3-3.7 GHz,the saturation output powers of Doherty power amplifier are 43.2-44.5 d Bm,the gains are8-11 d B,and the efficiencies are 42-56% and 67-76% under the condition of 6 d B back-off and saturation condition,respectively.The feasibility of the proposed scheme is verified. |
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