Research On High Efficiency And Linear Doherty Power Amplifier

In recent years,the development of wireless communication systems has been very fast,and there has been no slowing down.Today's mobile communication systems are required to have higher data throughput and lower power consumption,which poses greater challenges for designers of wireless transmitters.The RF power amplifier(PA)is a key module of the wireless communication transmitter,and its performance indicators directly affect the efficiency and linearity of the entire communication system.For increasing the data transmission rate,today's wireless communication systems have made significant advances in bandwidth and carrier,however,due to the memory effects of RF PAs,it's very difficult to design a power amplifier with a wide instantaneous bandwidth.In addition to bandwidth issues,wireless communication systems such as CDMA-2000,Wideband Code Division Multiple Access(WCDMA),and Orthogonal Frequency Division Multiplexing(OFDM)have large instantaneous transmit power,resulting in high peak-to-average ratio of RP signal power(PAPR).Therefore,the base station PA for the communication system must be highly linear to amplify the modulated signal with high PAPR.In order to meet linearity,the PA operates in Class A or Class AB and must operate with peak output power backoff,while efficiency at fallback is another important indicator of base station PA.Furthermore,the size and cost of the communication system are decreasing,and the cooling system is also simple and compact,so the efficiency enhancement technology becomes very important.High efficiency and high linearity PA design has become a hot issue.In this thesis,the working principle and characteristics of different power amplifiers are studied.A large amount of literatures are reviewed to find out the research progress and achievements of domestic and foreign.The design difficulties of high efficiency and high linearity RF PA are summarized.The source of memory effect and its influence on PA linearity are analyzed.To improve the efficiency and linearity of PA,this thesis proposes a double-bias network structure,designs a Doherty PA,and proves its feasibility through complete theoretical derivation.In addition,a new combiner is used to reduce the impedance conversion ratio,and replace the splitter in a traditional Doherty power amplifier with a 3dB coupler.This thesis uses CREE Semiconductor's GaN HEMT power amplifier tube CGH40010F,Rogers4350B sheet,designed a Doherty power amplifier working in 3.4-3.6 GHz(5G frequency band).Among them,the main amplifier works in class AB.The DC offset is Vds=28V,Vgs=-2.75V;the auxiliary amplifier operates in Class C,and the DC offset is Vds=28 V,Vgs=-6 V.After testing,the saturated output power of Doherty power amplifier is 43-44dBm,the drain efficiency more than 70%,at power back-off 6 dB the drain efficiency is 51%-55%,and power backoff of 8 dB is 43%.After adding digital pre-distortion,when the average output power reaches 42.5 dBm,the adjacent channel leakage ratio is lower than-46.5 dBc,these performances is effective compared with the current domestic and international power amplifier.