Design And Research Of Pulse Laser Ranging System For TDC Measurement Based On FPGA

Laser ranging technology has a wide range of applications in human production and life.It can be seem from engineering applications to manned spaceflight.Compared with other ranging methods,laser ranging has a long measuring distance,high precision and strong antiinterference ability.Laser ranging is mainly classified into pulsed laser ranging and phased laser ranging,for the pulse laser ranging system,the time difference between the transmitter and the target can reach the picosecond level because of the fast speed of light.Therefore,accurately measuring the time difference between the transmitter and the target is the key to improve the ranging accuracy of the system.In this paper,APD(Avalanche photodiode)sensor is used as the receiving chip,Zynq FPGA is used as the processing platform,and all the hardware circuits of the system are designed and verified,including nanosecond narrow pulse laser transmitting circuit,high voltage generating circuit and laser receiving circuit.In order to ensure the stable and normal operation of the system,three-dimensional model of optical transmitting and receiving parts is built specially,the shell is made by 3D printing to fix the laser and receiving lens,and all the hardware circuits verified are designed as PCB board and optical shell assembly,so that the laser emitted can be received stably.For the pulsed laser ranging system,the accuracy of TDC(Time-to-Digital Converter)measurement directly determines the accuracy of the system.In this paper uses the internal carry chain of FPGA to construct the delay chain,and realizes TDC measurement with encoder,coarse time counter,mean filtering and trigger module.In order to ensure the consistency of the delay chain,the whole CARRY4 carry chain is used as a single delay unit,and the total delay of the delay chain needs to be more than one clock cycle.Therefore,after a large number of experiments,160 delay units are connected in series to form a complete delay chain.In order to reduce the complexity of the design,this paper splits the 160-bit input encoder into five 32-bit input encoders,which is equivalent splitting the delay chain into five segments and then accumulating all the statistical results,greatly simplifying the design difficulty.The final measurement results show that the system's TDC measurement accuracy of the system can reach 63.3ps through FPGA,the ranging accuracy of the ranging system is 0.95 cm,and the measurement error is 0.91 cm.Compared with the commercial laser rangefinder on the market,this paper integrates TDC measurement into the internal of the FPGA,eliminates the special TDC measurement chip,not only improves the ranging accuracy and error of the system,but also reduces the complexity of the system hardware,saves the hardware cost,and can be transplanted to different platforms very flexibly.