Research Of Independently-tunable Concurrent Dual-band Doherty Power Amplifiers

With the rapidly development of the information technology, the growth of multimedia services, suchas voice, data, and video, has been explosive. With the time of big data and high speed rate communicationis coming, and mobile users prefer modern mobile communication system to be more fluent and real-time.In order to satisfy the needs of users, the third and fourth generation mobile communication standards havebeen put forward and implemented. The situation of multiple communication standards coexisting andmultiple communication bands divided presents in modern communication system. Multi-band andmulti-mode operation becomes a trend of future mobile communication system.Based on the existing implementation methods of multi-band and multi-mode power amplifier, anindependently-tuned concurrent dual-band Doherty PA and a tunable class AB power amplifier areproposed in this paper. Related research works as follows:(1) An independently-tuned concurrent dual-band impedance transformation network is proposed.Based on the study of traditional single-band impedance transformer, the proposed structure achieved thedesired transformation between different impedances in the concurrent and independently tuned bands byintroducing multi-stub transmission line and tunable component. Then the proposed structure is applied tothe design of3dB coupler. Except for concurrently working at0.9GHz and2.15GHz, the redesignedcoupler can also be tuned among2.0~2.3GHz around2.15GHz independently by changing the biasvoltages of varactors.(2) An independently-tuned concurrent dual-band Doherty PA is put forward. The main idea of themethod is to replace the single-band components of Doherty PA by the corresponding multi-band structures,and then realize the multi-band operation of the whole Doherty power amplifier. Considering therealizability and complexity of the proposed Doherty PA, the3dB coupler and input matching circuit aredesigned for independently-tuned concurrent dual-band operation, and the bias network, output matchingcircuit, offset line and power combiner network are designed for concurrent dual-band operation. Thespecific design methods and processes of the relevant units of the proposed Doherty power amplifier areanalyzed in detail in this paper, and finally with the help of ADS harmonic balance simulation, the proposedstructure is verified through large signal simulation. The simulated results indicate that the proposedDoherty power amplifier can be concurrently works at0.9GHz and2.15GHz, and it is also able to achievethe independently tuning operation among2.0~2.3GHz around the upper band while the frequencyresponses of the lower band remain unaltered. Among the concurrent and independently tuned bands, theoutput power at1dB compression point is up to40.79dBm, and the relevant PAEs are maintained above60%.(3) A varactor-based tunable power amplifier is realized. By introducing varactor diodes into theconventional hybrid matching network, the work frequency of matching network can be tuned by adjustingthe bias voltages of varactor diodes. For the bias network of the proposed power amplifier, it is designed toachieve broadband operation through the introducing of Fan-shaped microstrip line. And finally theredesigned power amplifier can be continuously tuning among the band of500~800MHz.