Research On High-efficiency And Linear Power Amplifiers Based On Active Load Modulation

Power amplifier(PA)is the main energy dissipation module of the transmitter and the main source of nonlinear distortion.With the complexity of signal modulation,the research on high power back-off efficiency and linear PAs is of great significance to the development of mobile communication system.Due to the limitation of the conventional passive matching networks,the optimal load impedance conflicts of the PA with one transistor at power back-off and saturation state makes it unable to meet the application requirements of high peak-to-average ratio signal.Active load modulated PA with its unique architecture has become a reliable solution in back-off applications.According to the above problem,an improved harmonic control network is proposed.After the study of PAs using waveform engineering,some solutions to achieve high power back-off efficiency or linear high-efficiency PA are proposed and verified based on the theory of active load modulation in this thesis.The research contents and innovations of this dissertation are summarized as follows:1.The design method of harmonic control network of the traditional inverse class-F PA is improved to achieve high-efficiency operation of peak output within the limited circuit size.A novel harmonic pre-control network is proposed and integrated in the package by modifying the design method of PA and the compensation of the parasiticelements.An inverse class-F PA based on harmonic pre-control network is designed.The PA delivers a saturation output power of 47.6-47.8d Bm over the operating band of 2.3-2.4GHz,and the drain efficiency is 75.2-76.5%.2.The design scheme combining pre-matching and post-matching technology is adopted to optimize the control signal power in load modulation balanced power amplifier(LMBA).Meanwhile,the saturation performance of the control amplifier(CA)is improved by the output topology based on harmonic pre-control network.A dual-input LMBA based on optimized CA is designed.The LMBA delivers a saturation output power of 50.5-50.8d Bm over the operating band of 2.5-2.7GHz.Meanwhile,the drain efficiencies are 58.2-64.8% and 55-62% at the peak output and 6d B back-off power level.Compared with the traditional high-efficiency PAs,the back-off efficiency has been improved significantly.3.The linearity of a Doherty PA(DPA)under different working conditions is improved.By analyzing the principle of nonlinear distortion,the key factors affecting the linear performance are summarized.The improved matching network and bias network topology are proposed to optimize the linearity of the carrier PA(CPA).Therefore,the linearity of the DPA under the low power condition is improved.Meanwhile,the linearity under high power condition of the DPA can be further improved by adjusting the cancellation of the third-order intermodulation.A linear high-efficiency DPA working over 2.5-2.7GHz is designed.At the center frequency,the DPA delivers a maximum twotone output power of 46.5d Bm at the condition of the third-order intermodulation distortion under-30 d Bc,and the drain efficiency is 56%.