FPGA Based Time Digital Conversion Design And Its Application In Pulse Radar

High precision time interval measurement is an important technology widely used in satellite navigation and communication,laser ranging,nuclear physics,medical imaging,geodynamics etc.While the technology developing,Measure methods varied and precision of time measurement improved.The current mainstream high-precision time interval measurement method is based on time-to-digital converter.ASIC or FPGA based TDC is the mainly two methods.The FPGA based TDC is mainly developed to overcome the issues of ASIC based TDC,including long developing time,high design cost and difficult to design.FPGA based TDC has many advantages in practical application,such as high system integration,easy to develop,easy to upgrade,low cost and good portability.Therefore,it is significant to design high precision FPGA based TDC.The ranging accuracy and range requirement of pulse radar determines the time measurement accuracy and range of TDC.The main work of TDC design including,setting the programmable logic element of the FPGA to build the delay line;a three stages coding method is proposed to design the coder,which is designed to eliminate the “bubble phenomenon” and the introduction of dead-time,as well as to decrease the occupation of FPGA resources;a calibration module is designed to calibrate the nonlinear of the delay line;a random pulse generator based on the characteristics of FPGA is designed to meet the calibration module demand;a global clock module and a data synchronization module are designed,because of the different clock of data transmission module and time measurement module;a counter is designed to measure the crude time.In order to verify the functionality of TDC,test platform is built and a lot of tests are made.The experimental results show that the time resolution of TDC with nonlinear correction is 85.34 ps,the differential nonlinearity of TDC is-0.38 LSB ?DNL ? 0.21 LSB,the integral nonlinearity of TDC is-0.25 LSB ? INL ? 0.4LSB.The maximum ranging error of pulse radar is 1.338 cm,and repetition frequency is 6.857 Mhz,which meets the demand.