| With the development of satellite communication,electronic countermeasures and other communication technologies,the modern communication system has put forward higher requirements for its linearization.The nonlinear distortion of power amplifier is the main source of nonlinear distortion in communication system and severely limits the power and efficiency of the communication system.Therefore,the research of power amplifier linearization technology has practical value and important significance.As one of the common linearization technologies of power amplifier,analog predistortion technology has become an irreplaceable linearization technology in satellite,aerospace and other fields because of its small size,simple structure,low cost,high stability,wide frequency band and other characteristics.In this thesis,the analog pre-distortion circuit based on Schottky diode is studied.Through the study of the nonlinear characteristics and equivalent circuit of the diode,the working principle of the pre-distortion circuit is analyzed.The circuit design process adopts the way of device independent design and overall optimization,and combines EDA simulation to verify and optimize the circuit performance.In addition,the improvement scheme is designed based on the theory of vector synthesis.And from the basic level,the design method of complex pre-distortion circuit is improved and innovated to improve the design efficiency.In order to meet the linearization requirements of the solid-state power amplifier(SSPA)in the frequency range of 19.6GHz~21.2GHz,a simple structure of reflective analog predistortion circuit is designed in this thesis.By changing the DC bias voltage of Schottky diode,the distortion characteristics of the predistortion signal can be adjusted.This circuit can provide about 1.2d B of power gain amplitude expansion and about 13° of power gain phase compression when the input power is increased by 6d B.On this basis,an improved reflective predistortion circuit is designed,which is powered by two Schottky diodes independently.The adjustable performance of the predistortion circuit can be increased by increasing the number of variable parameters.The improved predistortion circuit can provide about 1.7d B of power gain amplitude expansion and about 15° of power gain phase compression when the input power is increased by 6dB.In order to improve the adjustability and precision of the predistortion circuit,a double branch synthetic analog predistortion circuit based on vector synthesis theory is designed,which is composed of linear branch and nonlinear branch.The linear branch is a PIN diodebased attenuator,and the nonlinear branch is a Schottky diode-based nonlinear generator,and they are powered by different DC bias circuits.When the input power is increased by 6d B,this circuit can provide power gain amplitude expansion of more than 3.6d B and gain phase compression of more than 18°.Aiming at the problem that there are many kinds of bias voltage combination of double-branch predistortion circuit and it is difficult to select the appropriate bias voltage,a fast design method of double-branch predistortion circuit is proposed,which adopts the combination of mathematical optimization algorithm and EDA simulation.This method can split the bias voltage combination and reduce the simulation complexity.The effectiveness of this method is verified by the simulation design of doublebranch predistortion circuits,and it can be extended to the design of multi-branch predistortion circuits.The research work of this thesis still has many shortcomings,such as the difference between the measurement results and the simulation results,the circuit applicability is not high enough and so on.In the future,the analog predistortion circuit of power amplifier will be improved by updating the process,using integrated devices,optimizing the circuit structure and so on. |
PDF Full Text Request