Design Of Phase Laser Ranging System Based On FPGA

With the development of laser technology,laser ranging has gradually become a kind of important precision distance measurement technology.The raging system using lasers as transmitted waves has high ranging precision,small size,light weight,high resolution and strong anti-jamming capability,etc,Which is rapidly applied in the fields of terrain detection,missile range measurement,industrial production.Compared with other laser ranging technologies,phase laser ranging has the advantages of higher precision,faster measurement speed and simple instrument structure,which is widely used in the military and civil fields such as automobile anti-collision radar,geodetic survey,geological survey and water conservancy engineering.Thesis with semiconductor laser driver,phase difference frequency measuring technique and digital phase detector technology as the main research content,in view of the background noise,light circuit design,phase measurement error,etc,analyzing the influence factors in the improvement method is proposed.Besides,Based on the FPGA development platform,the phase measurement method is optimized to improve the stability and response speed of the system.Firstly,based on the principle of phase laser distance measurement and differential phase measurement,the overall design scheme of the system combining mixing technology and automatic digital phase measurement technology is determined.The transmitting system uses FPGA output control word,controls DDS chip to send out signal source,analyzes the characteristics of semiconductor laser,and designs a voltage-controlled constant current source to drive the laser to emit modulated light waves.The receiving system selects PIN photodiode as the detector,and designs a preamplifier circuit and an automatic gain control circuit to ensure the stability of the output signal gain,which is convenient for subsequent circuit processing.The received signal is sent to the FPGA after AD conversion.The signal is mixed by the multiplier to obtain the mixed signal.The FIR low-pass filter is used to filter the sum signal to obtain two 10 k Hz low-frequency sinusoidal signals with constant phase difference.Then,it is converted into a square wave signal by the zero-crossing comparator and sent to the RS trigger,and the phase is compared by a counter.Finally on the basis of automatic digital phase measurement,an improved multi-cycle synchronous digital phase measurement method is proposed,and the overall design of the mixing and phase measurement module is completed using FPGA,which can not only improve the measurement speed but also ensure the accuracy of phase measurement.The experiment proved that the stability of this method is very high,with the gate time being0.002s(n=20)and the phase stability better than 0.024 °.In this thesis,the feasibility of the system scheme is verified using a prototype.The experimental results show that the system has good linearity and stability,and the ranging error is less than 0.02 m.