Technologies For Multichannel TDC Of High Performance Based On FPGA

The TDC plays an important role in lidar applications of high-precision ranging,navigation,3D imaging and so on.Resolution,RMS accuracy,nonlinearity and other indexes of TDCs affect the performance of lidar.In this paper,the multichannel TDCs are designed based on the Artix-7 FPGA of Xilinx company in the background of lidar applications.The 16-channel tap-delay-line TDC and the 8-channel double-chain three-route TDC are designed for two airborne lidar applications.Two TDCs adopt a scheme of the coarse-fine measurement.In the tap-delay-line TDC,the carry chain is constructed by the cascading CARRY4 blocks.The core module of the other TDC is double-chain three-route structure and the fine time is represented by six data.Compared with the parallel six-chain TDC,this scheme can not only effectively create outstanding resolution,but also reduce the utilization of logic resources.Two schemes are designed to deal with the effect of temperature drift.Calibration chain structure includes three delay chains and the circuit periodically generates time interval signal.In the correction scheme based on XADC module,the temperature sensor integrated in XADC is used to monitor the temperature of FPGA and the data can be modified by the coefficient.A multichannel consistency correction scheme is designed to reduce the difference of measurement data between all channels.The correction factor ?(i)and the temperature range correction factor ?(i,j)are introduced to reduce the measurement difference of each channel of TDCs.The TDC test platform was built.In the tap-delay-line TDC,the average resolution value of all channels are 33.6ps at room temperature.The average values of DNL and INL are [-0.43,0.67] LSB and [-0.68,0.73] LSB respectively.In the double-chain three-route TDC,the average resolution value of all channels are 5.63 ps and the average values of DNL and INL are [-0.72,1.71] LSB and [-1.88,2.93] LSB respectively.Without correction,the RMS values are up to 53.7ps and 22 ps in TDCs of 85? by analyzing one channel.The former TDC parameter can be reduced to37.4ps based on the calibration chain scheme and 28.9ps based on the XADC temperature correction scheme.The latter TDC parameter can be reduced to 16.2ps based on the calibration chain scheme and 12.7ps based on the XADC temperature correction scheme.The consistency optimization factors of two multichannel TDCs are 0.79 and 0.72 respectively.