| With the rapid development of wireless communication,mobile communication technology has developed from scratch,from the first generation(1G)to the current fifth generation(5G)broadband high-speed communication.In broadband and high-speed communication demand,for increasing the requirements of the radio frequency front-end(RFFE),as the whole RFFE power consumption of the largest RF power amplifier,the output power,saturation efficiency,linearity parameters have a higher requirement.Therefore,the improvement of efficiency is of great significance to the improvement of linearity and the improvement of communication capacity.In order to adapt to the characteristics of 5G communication peak average ratio,Doherty power amplifier is usually used as the power drive level circuit in communication base stations.Doherty power amplifier began to develop towards multi-band work.At present,most of the multi-channel switch mode is used to achieve the multi-band working mode,which on the one hand increases the size of the overall circuit,on the other hand makes the energy loss in the process of hard switch increases.This results in an increased cost and lower performance of the base station operations.This paper analyzes the principle and structural characteristics of Doherty power amplifiers,and deeply understands some limitations and shortcomings of the dual-band bandwidth and backoff level of existing Doherty power amplifiers.On the basis of the introduction of power amplifier types,parameter indicators,matching methods,etc.,the limitations and shortcomings of Doherty power amplifiers are improved and perfected,and on the basis of introducing composite left/right hand(CRLH)transmission lines,the design of two dual-band concurrent Doherty power amplifiers in different application scenarios is finally completed.(1)A dual-band concurrent Doherty power amplifier based on a CRLH transmission line structure is proposed.The dual-band power divider and impedance inverter based on the CRLH transmission line structure are adopted,which can achieve the required phase value at any two frequency points,and at the same time control its own characteristic impedance,and can solve the limitation of insufficient bandwidth of traditional T-shaped structure and π-type structure in higher operating bands.In order to verify the rationality of the design,the CGH40006 P Ga N HEMT(High Electron Mobility Transistor)design was used to realize a concurrent Doherty power amplifier operating in the 3.3-3.6 GHz and 4.8-5.0 GHz bands,with more than 60% saturation drain efficiency in both bands,6 d B back-off efficiency of 44.4-51.6% and 43.5-50.1%,respectively,and saturated output power above 40 d Bm.(2)A phase shifter network based on CRLH transmission line structure is proposed.The phase compensation technology is used to place the phase shifter network at the output of the peak power amplifier so that in the low power input state,the peak power amplifier output end is as close as possible to the open of the Smith chart,so that the working state of the overall circuit is closer to the theoretical expectations.Expand Doherty’s back-off range while maintaining overall circuit efficiency to meet the growing peak-to-average signal.CGH40010 F and CGH40025 F were used to achieve a dual-band concurrent Doherty power amplifier operating at 0.7-0.8 GHz and 2.6-2.8 GHz,with more than 60% saturation drain efficiency in the operating band and 11 d B back-off efficiency of 45.2-60.5% and 42.8-46%,respectively.The saturated output power is above 45 d Bm.The design of the above-mentioned dual-band Doherty circuit can better verify the correctness and feasibility of CRLH transmission line theory applied to the design of active circuit.It also provides new ideas for the design of multi-band power amplifiers. |
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