Research Of Broadband And Large Output Power Back-off Doherty Power Amplifier

In order to meet the high-speed signal transmission in the coming 5G,the core component of the communication system,that is,the power amplifier,must meet higher and higher requirements.These include: broadband,high efficiency(under larger PAPR modulation signals)and digitization.Doherty power amplifiers have great potential as back-off efficiency enhancements in terms of bandwidth,high back-off efficiency,and ease of implementation.So,this paper will proceed from the basic theory of Doherty power amplifier,expanding its bandwidth and the amount of back-off in order to achieve better performance.The main research contents and innovations of this paper are summarized as follows:1.In this paper,we analyze the basic theory of active load modulation and Doherty power amplifier,and put forward that the use of quarter-wave transmission line limits the bandwidth of Doherty power amplifier.Based on these,a quarter-wave transmission line in a conventional Doherty power amplifier is replaced with a post-match structure and a broadband output matching network to extend its working bandwidth.And we have designed a Doherty amplifier working at 2.1-2.6 GHz.The experimental results show that in the design frequency band,the saturated output power is 43.4-44.2 dBm.The saturated drain efficiency is 54.8%-67.3%.And the drain efficiency under 6-8 dB output power back-off is 44.6%-58%.The measured saturated gain is: 11.5-13.4dB.In addition,the advantages of the die compared with the packaged transistor are analyzed.Based on this,a Doherty power amplifier designed for 5G applications is designed by the die.The experimental results show that at 3.3-4.3 GHz,the saturated output power is greater than 43.1 dBm;the saturated drain efficiency is greater than 58.6%;the drain efficiency is greater than 45% at 6 dB output power back-off interval;the saturated gain is 7-10.75 dB.Both of these Doherty power amplifiers have some advantages over recent reports.2.In this paper,we analyze the method and the basic principle of the load impedance solution for continuous class J amplifiers,and analyze the basic theory of asymmetric Doherty amplifiers to extend the back-off of traditional Doherty power amplifiers.Based on these,we design the asymmetric Doherty amplifier by usingimpedance solution of continuous class J amplifier.The author designed a wideband asymmetric Doherty power amplifier working at 1.8-2.6 GHz based on this model.Experimental results show that,in 1.7-2.5 GHz,the saturation output power of this Doherty power amplifier is 44.8-45.2 dBm;the saturation drain efficiency is 51.4%-67.8%,and the drain efficiency is 51.4%-67.8% under 9 dB output power back-off;saturated power gain is 8.2-13.2 dB.3.In this paper,the limitations of traditional single-input Doherty power amplifiers are analyzed.And an architecture of digital dual-input three-way Doherty power amplifiers based on amplitude and phase difference control is proposed.The simulation and experimental results show that the proposed structure can effectively eliminate the design constraints of Doherty PA with phase compensation line,fixed power ratio and depth bias class C amplifier in traditional single-input Doherty power amplifier.In order to verify the advantages of the structure,the author designed a digital dual-input three-way Doherty power amplifier operating at 3.4-4.2 GHz.The test results show that the Doherty power amplifier in 3.3-4.1 GHz: saturation output power is greater than46.5 dBm;the drain efficiency is greater than 49% under 9 dB output power back-off interval.