Research On Gan Mmic Doherty Power Amplifier And Its Key Technologies In 5G Communication System

With the rapid development of the 5^th generation of wireless technology（5G）,the wide use of massive multiple input multiple output technology and the use of new air interface frequency band with higher frequency make the miniaturization and integration of power amplifier（PA）imperative.To further improve the peak transmission rate of data and the utilization of spectrum resources,the bandwidth of the modulated signal is becoming larger and larger,and the modulation mode is becoming more and more complex,which makes the peak to average ratio of the modulated signal larger and larger.Doherty PA（DPA）is a widely used PA architecture in wireless communication base station systems for the reasons of high back-off efficiency,but it faces many design challenges in terms of bandwidth,efficiency,linearity,and size,especially for the millimeter wave（mm-wave）band DPA design.In this paper,Sub-6-GHz and mm-wave gallium nitride（GaN）monolithic microwave integrated circuit（MMIC）DPAs used in 5G communication systems are deeply studied to further broaden the bandwidth,improve the back-off efficiency,and realize the miniaturization of the GaN MMIC DPA,to meet the needs of transmitters in 5G communication systems.The main research work and innovations of this paper are as follows:（1）An mm-wave synchronous GaN MMIC DPA with the enhanced load-modulation is proposed.By reducing the phase dispersion factor of the load-modulation network,the bandwidth of the DPA can be expanded and the best saturation characteristics can be achieved in the mm-wave band.The optimal tuning method of designing an equivalent quarter wavelength line（EQWTL）with a minimum phase dispersion factor is given.The influence of the input power division ratio on the load-modulation behavior of the DPA is systematically analyzed,which provides a theoretical basis for selecting the input power division ratio reasonably to enhance the load-modulation of the amplifier.The fabricated 24-28 GHz GaN MMIC DPA developed by a 0.15-um GaN-HEMT process can achieve a saturated output power of 35.4-36 DBM and a saturated efficiency of 27.8%-36.8%.The 6-dB power back-off（PBO）efficiency is 18.3%-30.1%and the 9-Db PBO efficiency is higher than 14.3%.The400 MHz instantaneous bandwidth modulated signal is used for testing.After digital predistortion（DPD）,the adjacent channel leakage ratio（ACLR）is improved to-40 dBc,and the error vector amplitude（EVM）is 2.76%.At this time,the average efficiency is 27.4%.The above research results have been published in the international core journal IEEE Transactions on Microwave Theory and Techniques.（2）An asymmetric mm-wave GaN MMIC DPA based on equivalent parallel power cells（EPPCs）technology is proposed.The power stage transistor of the peaking amplifier is realized by using the EPPCs technology,and the output capacitance(C_out)of each parallel transistor is resonate out by using a parallel inductor,while the C_out of the carrier amplifier’s power stage transistor is absorbed,which solves the problems of low gain,low output impedance,and low saturation efficiency of the large-size peaking power-stage transistor in the traditional mm-wave asymmetric DPA so that better broadband characteristics are achieved.The 24-28 GHz asymmetric GaN MMIC DPA fabricated by a 0.15-um GaN-HEMT process has a saturated output power of 35.4-37.6 dBm and a corresponding saturated efficiency of 23.7%-34.4%.The efficiency at 8-dB and 9-dB PBO are 15.5%-30.7%and14.3%-28.8%respectively.When excited by a 400-MHz broadband modulation signal,the average efficiency can reach 29%.After DPD,the ACLR is-40 dBc and the EVM is 2.76%.To the best of the author’s knowledge,the proposed DPA has the highest 8-dB and 9-dB PBO efficiency among all the reported 2-stage MMIC DPAs in the mm-wave band.The above research results have been submitted to the international core journal IEEE Transactions on Microwave Theory and Techniques.（3）Aiming at the efficiency improvement and miniaturization of Sub-6-GHz GaN MMIC DPA,a new harmonic impedance matching method by using a single parallel LC resonant block for harmonic impedance post-matching and an improved broadband compact load-modulation network are proposed.The second harmonic load impedance of the carrier and peak amplifier can be matched to the best region at the same time by using only one parallel LC resonant network.By combining and optimizing twoπ-type high-pass EQWTLs,an improved load-modulation network is formed,which widens the bandwidth and improves the efficiency.Two Sub-6-GHz GaN MMIC DPA were fabricated using 0.25-um GaN-HEMT process.In addition,to solve the high cost of the monolithic integration scheme,a 3.4-3.8GHz GaN quasi-MMIC DPA with load-modulation network based on fully distributed inductors is developed.The test results show that the saturated output power of 30 W and the saturated drain efficiency of 60.4%-66.5%are achieved,and the 8-dB PBO drain efficiency is45%-49%.The above research results have been published in the international core journals IEEE Microwave and Wireless Components Letters and Electronics Letters,as well as the2019 IEEE International Symposium on radio frequency integration technology（RFIT）and the 2021st 51st European Microwave Conference（EUMC）.（4）Aiming at the bandwidth broadening problem of Sub-6-GHz GaN MMIC DPA,the influence of the C_out of the peaking transistor biased in Class-C state on the bandwidth characteristics of GaN MMIC DPA is theoretically analyzed,and a hybrid matching method is proposed.A simple T-shaped band-pass network is used to match the peaking amplifier,and the C_out of the peaking transistor working in Class-C state is properly compensated.A proper load-modulation is achieved while broadening the bandwidth.The 4.6-5.5 GHz broadband high-efficiency GaN MMIC DPA developed by a 0.25-um GaN-HEMT process has a saturated output power of more than 41.1 dBm,a saturated drain efficiency of more than 57.6%,and a 6-dB PBO efficiency of 51%-56.4%.Excited by a 160-MHz modulated signal,the average efficiency of the amplifier can reach 54%after using DPD technology,and the ACLR is improved to-47 dBc after DPD.The above research results have been published in the international core journal IEEE Transactions on Circuits and Systems I:Regular Papers.（5）A wideband mode switchable GaN DPA based on dual reactance compensation and adjustable drain voltage technologies is proposed.The wideband mode（WB-MOD）and the dual-band mode（DB-MOD）with a larger PBO range can be switched by one key through the dial switch,and the relative working bandwidth of 124%can be achieved by using a single input architecture.To solve the problem of insufficient load-modulation in dual-band mode,an optimal load resistance enhancement technique is proposed by simultaneously adjusting the drain voltage of the carrier and peaking amplifiers.Measurement results show that the amplifier can achieve a saturated output power of higher than 43.4 dBm and a saturated drain efficiency of 51.3%-70.3%in the bandwidth of 0.8-3.4 GHz.The operating frequency of the WB-MOD is 1.3-2.9 GHz,while that of the DB-MOD is 0.8-1.3 GHz and 2.9-3.4 GHz.In WB-MOD,the 6-dB PBO efficiency of the DPA is 45.3%-56.1%,while in DB-MOD,the8-dB PBO efficiency of the amplifier is 41.6%-57.9%.The above research results have been published in the international core journals IET Microwave,Antennas&Propagation,and the international conference 2020 IEEE Asia Pacific Microwave Conference（APMC）.