| With the adoption of OFDM system modulation technology in digital TV transmission system,the demand of larger capacity and higher transmission rate makes the signal peak-to-average ratio increase continuously.At the same time,the requirement of digital TV transmitting frequency band makes the broadband and high efficiency of RF front-end power amplifier module become inevitable.Doherty power amplifier is widely used because of its simple and easy to design structure and high efficiency in power backoff.The traditional Doherty power amplifier can’t meet the requirements of digital TV transmission system due to narrowband effect brought by the quarter wavelength and the power back-off range of 6 d B.Therefore,this thesis focuses on the research of wide-band high efficiency Doherty power amplifier and high-power back-off Doherty power amplifier.The bandwidth,efficiency and power backoff of Doherty power amplifier are the hot topics of research in recent years,and the selection of appropriate architecture and design ideas to design has become the main starting point.In view of the above problems,relying on the project entrusted by Liaoning Putian Digital incorporated company,research work is carried out.The main achievements are as follows:(1)A wideband post-matching Doherty power amplifier based on second harmonic suppression is proposed.A post-matching structure with second harmonic suppression is designed based on the idea of inductive coupling,and the second harmonic control of carrier power amplifier at the back-off point is processed in the post-matching load modulation network,so as to realize the high efficiency of the Doherty power amplifier during the power back-off.For the output matching of the peak power amplifier,the quasi-elliptic filter structure is used to design the harmonic wave,so as to improve the saturation efficiency.The proposed Doherty power amplifier structure is tested in real life.In the range of 470-650 MHz,the saturation efficiency of the designed Doherty power amplifier is more than 68%,and the 6d B power back-off efficiency is between 48%-65%,which meets the design requirements of the company’s entrusted project.(2)An asymmetrical high backoff Doherty power amplifier based on reactance compensation is proposed.The output impedance of the proposed asymmetric Doherty power amplifier is pure reactance impedance during power back-off.The traditional calculation formula of asymmetric Doherty power back-off can be extended by selecting smaller power ratio and pure reactance impedance.In the design of output matching of two branches,double impedance matching is adopted to reduce the bandwidth limit caused by the compensation line,so as to effectively expand the bandwidth.The test results show that the saturation output power of the designed amplifier is greater than 42.8 d Bm,the peak power is 43.3 d Bm,and the efficiency is between 45% and 59% for the 9.5 d B power back-off point in the500-650 MHz bandwidth.Compared with the traditional asymmetric Doherty power amplifier,the same power backoff is achieved when the power ratio is reduced,indicating that the proposed method has a good application background. |
PDF Full Text Request