Research On High-Efficiency Broadband/Dual-Band Radio-Frequency Power Amplifier

Power amplifier(PA)is one of the most important components in the RF front-end system,its performance has a vital impact on the RF communication system.Thus,how to improve the performance of RF PA is a hot spot in the communication field.On the one hand,to meet the requirement of ever-increasing number of frequency bands,extensive research has been conducted to develop broadband/dual-band PA.On the other hand,to enhance the efficiency of PAs under the excitation of high peak-to-average power ratio(PAPR)signals,various techniques such as load modulation techniques including Doherty and Outphasing PAs are widely used in communication systems.In addition,to meet the requirement of high integration,the method of co-design which integrates multi function into one circuit can simplify the circuit and realize high integration and low loss.Therefore,this paper will focus on the aforementioned issues.Firstly,an ultra-wideband mixed-continuous PA is designed to meet the requirements of multi-mode communication.Then,broadband Doherty PAs are designed to meet the requirements of high PAPR.Finally,in view of the scenario of dual-mode communication,Outphasing and Doherty PAs with dual-band filtering response are designed to not only realize high back-off efficiency but also to suppress the out-of-band interference.Especially,the main research contents are as follows:(1)An ultra-wideband high-efficiency mixed-continuous mode PA based on elliptic low-pass matching network is designed with an operating frequency range of 0.5-3.15 GHz,the fractional bandwidth is 145.2%.To design the PA with optimal performance within the operating bandwidth,a combination of continuous inverse Class-F and extended continuous Class-F modes is adopted.The combination of these two modes can significantly expand the design space and thus the design of matching network has greater design freedom.The proposed quasi-elliptic low-pass matching network can realize a broadband impedance matching in the predefined optimal impedance region desired by the combination of the continuous inverse Class-F and extended continuous Class-F modes.Simultaneously,transmission zeros are generated near the passband and a wide stopband covering up to the third harmonic is achieved,which exhibits high skirt selectivity and good harmonic suppression.Within the operating bandwidth,the drain efficiency is measured as 58-74.9%.(2)A miniaturized broadband Doherty PA(DPA)using simplified output matching topology is proposed.In the conventional broadband DPA designs,post-matching networks are usually added after the combing node to realize impedance transformation and reduce the impedance transformation ratio of modulation network.For the post-matching network,it usually occupies large circuit size.To solve aforementioned issue,in this design,two ideal transformers are firstly introduced in the carrier and peaking branches to replace the post-matching network.Then,by rearranging the output matching components in the two branches,Norton transformation can be used and the ideal transformers can be eliminated without increasing complexity.In this way,the impedance at the combining node is directly matched to a 50-Ω load without using a post-matching network,resulting in both compact size and wide bandwidth.Based on the aforementioned technique,a broadband DPA with operating bandwidth of 1.3-2.8 GHz is designed.Within the operating bandwidth,the measured 6-d B back-off efficiency is ranged from 41.8% to 61%.Moreover,the proposed design can also be applied in the scenario of a large impedance transformation ratio.(3)An ultra-wideband DPA based on quarter-wavelength(λ/4)transmission lines with negative characteristic impedance is proposed for bandwidth extension.In conventional DPA designs,the load modulation network is frequency-dependent,leading to bandwidth limitation at the back-off power region.In this design,by integrating two λ/4 transmission lines with negative characteristic impedance into the main and auxiliary branches to manipulate the impedance at the back-off power,the efficiency at back-off power is enhanced over a wide frequency range.In the implementation,the two negative characteristic impedance λ/4transmission lines are replaced by paralleled lumped-element LC resonators with negative values.The negative capacitors can be eliminated by combing the paralleled capacitors in theπ-shaped networks which are modeled as series transmission lines.While the negative inductors were eliminated by introducing Norton transformation.Based on the proposed method,a broadband DPA with operating bandwidth from 0.6 to 2.8 GHz is implemented.Within the operational bandwidth,the measured 6-d B back-off efficiency is ranged from 35.4%to 52%.(4)A high-efficiency dual-band filtering Doherty power amplifier(DPA)based on multi-function circuits is proposed to meet the requirements of the dual-mode communication system with high PAPR.The multi-function circuits include a tri-function dual-band filtering power combiner and a dual-function dual-band impedance control network.A dual-band filtering power combiner also plays the role of real-to-real impedance matching,in which one resonator is shared by both the power combing and filtering circuits.Transmission zeros are generated between the two passbands,realizing a sharp roll-off rate and greatly enhancing the isolation between the two passbands.Meanwhile,an impedance control network is designed to simultaneously suppress the harmonics and transform the optimized complex impedance desired by the transistor to a real one.In this way,the output matching network and extra filter in conventional design are realized by the filtering power combiner and impedance control network in the proposed design,resulting in a simpler structure.A dual-band DPA operating at 2.14 and 2.6 GHz is implemented with the measured 6-d B back-of efficiencies of50% and 57%,respectively.Moreover,the proposed method can also be used to design an Outphasing power amplifier and can be applied to any two operating frequencies.