A Multihit Time-to-Digital Converter Architecture on FPGA

We present a multihit time-to-digital converter (TDC) architecture implemented in a field-programmable gate array (FPGA) with minimized timing overhead. The TDC circuit provides two-level fine-time interpolation. The fine interpolator is a matrix of Vernier delay cells interconnected in a topology to provide two propagation paths for the incoming data pulse. Two methods of calibration are presented to estimate the component delays. The TDC circuit achieves time measurements with a resolution of 75 ps with an average precision of ~ 300 ps and is capable of detecting incoming pulses at a distance of 7.5 ns or more from each other.