Research On Broadband High Efficiency Doherty Power Amplifier Based On Improved Combined Network

The revolution of mobile communication system from generation to generation has brought severe technical challenges to power amplifier,which is the core component of RF(Radio Frequency)front-end system,while continuously improving the system and providing faster and faster transmission rate.Based on the design of load modulation network of Doherty power amplifier and the analysis and selection of back-off impedance,this thesis proposes two broadband and high efficiency Doherty RF power amplifiers adapted to peak-to-average ratio(PAPR)signals,which realize the improvement of back-off efficiency and the expansion of working bandwidth.The main contents and innovations of this thesis are as follows:A load modulation network based on Rotated T-shape structure is proposed.By analyzing the bandwidth improvement of this structure over the traditional quarter-wavelength impedance converter,the importance of improving the load modulation network for improving the bandwidth of Doherty power amplifier is further demonstrated.In addition,the optimization process of broadband load modulation network is given.Finally,a broadband Doherty design example is given to verify its high efficiency and broadband characteristics.The working bandwidth of the power amplifier based on rotated T-shape load modulation network is 2.1 GHz-2.6 GHz,the output power is 40.8 dBm-43.1 dBm,and the drain efficiency is 52.2-67.4%and the saturated drain efficiency is 66.4-82.4 at 6 dB back-off.An improved design method of combined circuit network based on back-off impedance is proposed.The non-ideal open-circuit effect of auxiliary power amplifier at the back-off point helps to expand the design range of main power amplifier in the back-off area.By optimizing the design of matching network and analyzing parasitic parameter network of main power amplifier,the output impedance of auxiliary power amplifier is taken into account when it is not open,so that the main power amplifier works in continuous F-1 mode at the back-off point,thus further expanding the bandwidth,improving the efficiency and improving the performance of edge band.The improved Doherty power amplifier based on backoff-impedance has a working bandwidth of 1.8 GHz-2.7 GHz,an output power of 42.0 dBm-45.8 dBm and a drain efficiency of 52%-64%at 8 dB back-off according to the measured results.