| The power amplifier(PA)is an indispensable part of the modern communication transmitter system.Many studies have been conducted to improve the performance of PAs.In order to serve the needs of massive communication devices,enhanced mobile broadband,and ultra-reliable low-latency communications,PA designers are facing the challenges of designing PAs with high efficiency,wide bandwidth,and large peak-to-average ratio,etc.In ultra-wideband applications,the coincidence of low-frequency harmonics and the high-frequency fundamental wave generally results in the impedance conflicts;In high peak-to-average ratio signal applications,impedance conflicts also exist due to different optimal impedances of the low power level and high power level.While it is a challenge for conventional passive matching networks to provide solutions to the above impedance conflicts,active load modulation technology can improve the flexibility of impedance configuration.This dissertation aims to solve the above problems by studying separate power amplifier active load modulation technology theories and architectures to solve the above problems.The main contents and innovations of this dissertation are as follows:1.The conventional resistance-reactance continuous working mode is improved.An active harmonic load modulation structure based on minimum power injection is proposed,which solves the problem of low-frequency harmonics and high-frequency fundamental impedance conflicts in cross-octave applications,thereby achieving ultra-wideband high-efficiency PA.The first step is adding the harmonic parameter factors to the voltage waveform of the resistance and reactance terms.The optimal impedance solution space is further expanded,and the flexibility of broadband matching is improved.A high-efficiency broadband PA working at 2.2-3.8 GHz is designed,with the output power of 10.7-16.8 W,the drain efficiency of 63.4%-72.9%,and the saturation gain of 10.1-10.9 d B in the working frequency band.Secondly,in cross-octave applications,the harmonic impedance of the main PA can be changed by way of harmonic injection through the load modulator to obtain different working modes in the low-frequency and high-frequency bands.Simultaneously,a minimum harmonic injection method based on negative resistance analysis is proposed,which has achieved the effect of improving the efficiency of the entire system.A high-efficiency dual-band power amplifier operating at 1.7 GHz and 3.4 GHz is designed,which achieves an output power of 40.6 d Bm and 41.3 d Bm and overall efficiency of 65% and78.5% without the harmonic injection.The power and overall efficiency at 1.7 GHz is increased to 41.3 d Bm and 78.6% with the harmonic injection.2.Two types of active fundamental load modulation structures have been improved.One is to improve the asymmetric Doherty power amplifier(DPA)structure combined with continuous Class-F working mode;the other one is to propose a symmetric DPA structure based on phase analysis and matching sub-network co-design.It solves the bandwidth limitation problem caused by the conventional quarter-wave impedance inversion line and the output isolation condition of the peaking PA in the large back-off applications,thereby achieving the large power back-off asymmetric and symmetric broadband DPAs,respectively.First,the continuous Class-F mode theory and the asymmetric DPA structure are combined,and the bandwidth and power back-off of DPA are expanded at the same time.A DPA operating at 1.8-2.6 GHz is designed,which achieves an output power of 44.8-45.2 d Bm,and the 9-10 d B back-off efficiency of49.6%-63.4%;Secondly,a symmetrical broadband DPA with configurable power back-off region is proposed.After analyzing the phase of the output matching network of the carrier and peaking PA,the frequency response of the post-matching network is introduced,and a symmetrical broadband DPA that works in large power back-off is obtained.A DPA operating at 1.9-2.5 GHz is designed,with a saturated output power of44.1-44.8 d Bm and an 8.5-9 d B back-off efficiency of 44.2%-49.7%.3.We improve the active load modulation balanced power amplifier(LMBA)and adopt the post-matching dual-input structure to expand the bandwidth.Besides,an automatic power amplifier design method is proposed,which solves the complicated process and non-convergence of simulation and optimization in conventional PA design,thereby shortening the design cycle.First,a method that can realize automatic PA design under different requirements is proposed,using the improved simulated annealing particle swarm optimization,and verified by designing a broadband and tri-band PA.The frequency band of the broadband PA is 0.8-3 GHz and the saturated output power and drain efficiency are 39.4-42.4 d Bm and 55%-68.5%,respectively;The frequency bands of the three-band power amplifier are 3.35-3.55 GHz,5.75-5.95 GHz and7.65-7.95 GHz.The saturated output power are 36.5-38.4 d Bm,37.9-38.6 d Bm and37.1-37.7 d Bm,and the corresponding drain efficiency are 50.1%-65.7%,44.2%-50.4%and 41.8%-54.3%.Secondly,in order to further expand the bandwidth of the LMBA while reducing the size,the post-matching technology is introduced into the dual-input LMBA architecture.An LMBA operating at 2.5-3.5 GHz is designed,with a saturated output power of 46.6-47.6 d Bm and a 9 d B back-off efficiency of 52.7%-66.9%.In summary,the dissertation studies three aspects of active load modulation and explores its potential in high-efficiency,ultra-wideband,and large back-off performance by improving the theory and structure. |
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