Driver Source Design And Frequency Nonlinear Correction For FMCW Lasers

Frequency Modulated Continuous Wave(FMCW)lidar ranging technology is an advanced non-contact measurement technology,which fully combines the characteristics of laser measurement technology and modern photoelectric technology,it has the advantages of high measurement accuracy,strong reliability and little environmental impact.Frequency modulated continuous wave laser radar ranging technology is based on the linear frequency modulation of the transmitted signal,so the frequency modulation linearity of the transmitted signal affects the accuracy of the ranging technology to a large extent.However,in practical applications,due to the limited accuracy of the driving current and the nonlinearity of the frequency modulation of the laser itself,the linearity of the laser output signal frequency is poor,which indirectly leads to inaccurate measurement results.Aiming at the above problems,this dissertation designs a new high-precision FMCW laser driving source according to the principle of arbitrary waveform generation technology to improve the accuracy of the driving current.Secondly,a frequency correction algorithm based on the optimization of relative nonlinear error is designed by using the current compensation method iteration to correct the frequency of the laser output signal,so that the time frequency curve of the laser output signal can reach the maximum linearity,so as to ensure the measurement accuracy of the frequency modulated continuous wave laser radar ranging technology.The main research work of this dissertation is as follows:1.The principle of FMCW lidar ranging technology is analyzed.The driving current accuracy of current tunable semiconductor lasers and the influence of frequency modulation nonlinearity on ranging accuracy are analyzed.The method of current compensation iteration is adopted to improve the frequency nonlinearity.For AA1416 distributed feedback laser,the relevant parameters of FMCW laser driver are determined.2.The design scheme of FMCW laser driver is determined and the circuit is designed.Using Complex Programming Logic Device(CPLD),external SRAM and digital to analog converter to design arbitrary waveform generation circuit has higher precision and greater flexibility.In a current modulation cycle,the number of sampling points reaches 25000.At the same time,a 16 bit resolution digital to analog converter is used in any waveform generation circuit to ensuring the current accuracy.In order to reduce the influence of temperature,the constant current source circuit adopts such means as increasing the heat dissipation area and selecting low temperature drift devices to reduce the influence of temperature on the accuracy of output current.In addition,the Ethernet communication program of the FMCW laser driver source card and the arbitrary waveform setting program based on ARM processor are designed,and the current waveform control software of the upper computer based on MATLAB is designed to control the FMCW laser driver source card to change the output current waveform.3.A frequency nonlinear correction scheme is designed for the frequency modulation nonlinearity problem of the laser.The frequency nonlinear correction algorithm is researched based on the relative nonlinear error using the current compensation iteration method.The time frequency curve of the actual laser output is analyzed by the beat signal,The relative nonlinear error is calculated with the ideal output time frequency curve,and the next drive current is corrected with the relative nonlinear error,iterative correction is repeated to improve frequency nonlinearity.The experimental results show that the output current of the designed FMCW laser driver can be adjusted continuously,the resolution can reach 0.01 m A,and the error is less than 0.028%,which can meet the requirements of the semiconductor laser.The proposed correction algorithm based on relative nonlinear error optimization can quickly and effectively improve the frequency modulation nonlinearity of currenttuned semiconductor lasers.The frequency nonlinearity is reduced from 11.16%before correction to 0.017% after repeated correction through multiple correction algorithms.The linearity of the output time-frequency curve of the laser is increased by more than 650 times.The nonlinear problem of frequency modulation is improved effectively and the accuracy of FMCW laser ranging technology is guaranteed.