Design And Implementation Of FMCW Source System Utilizing Inner Modulation

This article mainly studies the process of generating FMCW laser source through inner modulation,including the design of distributed feedback(DFB)laser driving circuit,ultrafast broadband DDS swept-frequency source circuit,and microstrip stepped impedance low-pass filter using ADS simulation software and the application in the area of frequency modulated continuous wave laser ranging.Since the current and temperature have an influence in the stability of the output laser power of the semiconductor laser,it is necessary to ensure that the laser driving circuit has functions of constant current driving and constant temperature controlling.Moreover,frequency modulated continuous wave laser ranging requires that the modulation source has the characteristics of large enough modulation bandwidth and short enough modulation period.Therefore,to achieve an ultrafast broadband DDS swept-frequency source is the key point of this article.This article focuses on the design of the FMCW laser source,and analyzes the design of DFB laser driving circuit and the ultrafast broadband DDS swept-frequency source in detail.The constant current driving circuit of the source system adopts thecurrent feedback operational amplifier controlling method to make sure that the error of the driving current is within ±0.05 m A.Based on the Peltier effect of semiconductor material,the constant temperature controlling circuit of the DFB laser is designed so that the error of the temperature controlling is within ±0.1?.The laser driving circuit with the functions of constant current driving and constant temperature controlling ensures that the error of the laser power output is within ±0.1m W.With the Tina-TI simulation software,the modulation effect of swept-frequency source with the bandwidth of 100MHz-1GHz is simulated and analyzed,and the result shows that a relatively ideal modulation effect is achieved.The DSP28335 chip is used to control the AD9914 to design an ultrafast broadband DDS sweptfrequency source with a range of 100MHz-1GHz and a sweep period of 8.8us.A microstrip stepped impedance low-pass filter is designed using ADS simulation software to decrease the in-band attenuation,and make the output curve flatter.The actual characteristics of the low-pass filter meet the index using layout simulation.In this thesis,by the way of inner modulation,the FMCW source system which is combined the stable DFB laser driving circuit with the ultrafast broadband DDS sweptfrequency source is designed.Based on the working principle of the FMCW laser source,the basic theory and design scheme of each functional module are introduced in detail.In order to avoid the occurrence of overcurrent from the laser source,LD electrostatic protection circuit and TEC clamp controlling circuit are given.Finally,the FMCW source system utilizing inner modulation is completed.