Research On Linearization Technology Of Power Amplifier For 5G Applications

The external linearization techniques for power amplifiers(PAs)can maintain a trade-off for the contradiction between the efficiency and linearity of the communication system.The multiple-input multiple-output(MIMO)architecture and signals with a higher carrier frequency,wider bandwidth,and higher peak-to-average ratio(PAPR)are used in the fifth-generation mobile communication system(5G)to achieve higher transmission rates.These scenarios put more performance requirements on linearization techniques.Compared with digital predistortion(DPD),analog linearizers have a simpler implementation,wider operating bandwidths,and lower cost.However,the low linearization performance of conventional linearizers restricts its application in communication systems.This dissertation focuses on the design theories and innovative architectures of linearizers to meet the performance requirements of 5G.The main contents and innovations of this dissertation are as follows:1)Two new operating modes of linearizer have been extended from conventional linearizer which has a correlated expansion characteristic of amplitude and phase,then a linearizer design theory based on self-compensation of amplitude and phase(SCAP)between different operating modes is proposed,which solves the problem that the conventional linearizer is difficult to accurately compensate the amplitude/phase distortion of the PAs at the same time due to its high amplitude-phase correlation.A linearizer working from 3.4 to 3.6 GHz is designed and fabricated,the measurement results show that the independent and continuous tuning range of the linearizer is obtained by more than 30? and 3 d B.When stimulated by several wideband signals,two different PAs achieve over-40 d Bc of Adjacent Channel Power Ratio(ACPR)with up to the bandwidth of 55 MHz,and good linearity is obtained with the carrier power back-off.The proposed linearizer can significantly improve the linearity of PAs without co-design and does not increase the power and control consumption compared to conventional analog linearization.The results reveal that the linearizer has flexibility and universality of design and use in communication systems.2)This dissertation proves that PA's static nonlinearity and memory effect is mainly related to the carrier and envelope frequency of the excitation signal,respectively.Based on the relation between nonlinearity and frequencies,a method of digital/analog dualdomain hybrid linearization(DDHL)is proposed,which uses the linearizer and DPD to compensate the static nonlinearity and memory effect of PA with wideband signal stimulated respectively.The DDHL solves the problem that the linearizer cannot compensate for the memory effect and reduces signal processing cost.The results show that the nonlinearity order is reduced from 8(32 parameters)of DPD to 5(20 parameters)of DDHL at ACPR of-50 d Bc,and the Normalized Mean Square Error(NMSE)and ACPR are improved by 2 d B.3)A linearization solution for Doherty PAs(DPAs)based on linearizers with SCAP is proposed,which solves the problem that the existing linearizers cannot accurately compensate the complex nonlinear characteristics of the DPA.A DPA with 8 d B back-off is tested using the linearization solution at 3.5 GHz with a 20 MHz signal,and the ACPR is improved from-32.3 d Bc to-44.9 d Bc.The back-off and gain characteristic of the linearization solution can be configurable to match the DPA,the proposed solution has a simple control mode and does not need co-design with the DPA,which shows its potential in complex modulation systems.4)In this dissertation,the bandwidth limitation of conventional linearizers is analyzed,and a linearizer method based on broadband load match network(LMN)is proposed,the method can realize a broadband linearizer with constant-voltage bias by synthesizing the LMN.Then a method of design space expansion for linearizer with constant-voltage bias is proposed,the method can reduce the design complexity and achieve good broadband performance.These methods solve the problem that the broadband characteristic of the conventional linearizer depends on the bias tuning of the nonlinear device,the contradiction between the bandwidth,performance,and control cost of the linearizer is reconciled.Two linearizers with constant-voltage bias working from29 to 31 GHz and 40 to 43 GHz,are designed and measured respectively.By using the linearizers,the output 1-d B compression power of two PAs has increased by more than1.2 d B and 1.7 d B,the third-order intermodulation distortion(IMD3)of two PAs is improved by more than 12.2 d B and 8.6 d B with a 100 MHz two-tone signal stimulated.