The Research Of Digitally Assisted Dual-Input Doherty Power Amplifier

With the new generation 5G mobile communication system is coming,the requirements for performance indicators are higher,such as efficiency and bandwidth.As one of the critical components in wireless communication systems,the power amplifier(PA)will also face such requirements.And Doherty PAs have been widely used in base stations due to high back-off efficiency and easy realization of the structure.However,although the traditional Doherty PA has a simple structure,it still has some inherent defects which affect its efficiency and RF bandwidth.In recent years,digitally assisted Doherty PAs are becoming an increasingly interesting alternative to conventional Doherty PAs.Studies have shown that they can greatly improve the performance of traditional Doherty PAs,such as efficiency,bandwidth and power.Therefore,starting from the basic principle of Doherty PA,this thesis focuses on the research and design of digitally assisted Doherty PAs with separate RF inputs,aiming to effectively improve the operating bandwidth,efficiency at back-off region and output power of Doherty PAs.The main research contents are summarized as follows:1.This thesis analyzes the basic principle of active load modulation of Doherty PA and the reason why the use of quarter-wavelength lines limits the bandwidth of Doherty PAs,and the author decides to use impedance inversion network and post-matching network structure to replace quarter-wavelength lines.Based on this structure,the author designed a Doherty PA working at 3.5GHz.2.By analyzing the factors that limit the performance of traditional single-input Doherty PAs,the author decides to utilize digitally assisted technologies in Doherty PAs.Based on this structure,the author designed a digital dual-input Doherty PA whose operating frequency band is 4.6-5.2GHz.The experimental results show that the saturated drain efficiency of the dual-input Doherty amplifier is 51.7%-55.8% in the operating band;the efficiency is 39.1%-43.5% under 6d B back-off.And the saturated output power is 39.64-40.43 d Bm.3.This thesis analyzes the specific structures and design methods of the dual-frequency matching network.Based on the basic theory of dual-frequency impendance matching and combined with the structure of digital dual-input Doherty PAs,the author designed a dual-band digital dual-input Doherty PA working at1.8-1.9GHz and 3.4-3.5GHz,which can be applied to 4G and 5G wireless communication systems.Its applicability is stronger.The test results show that the saturated drain efficiency of the dual-input Doherty amplifier in the frequency bands of1.8-1.95 GHz and 3.4-3.45 GHz is 46.1%-66.4% and 47.2%-51.3%;the efficiency is41%-49.9% and 46.1%-49.3% under 6d B back-off.And the saturated output power is42.66-43.84 dBm and 43.04-43.5dBm.