An FPGA-based, high-precision, narrow pulse width measurement time-to-digital converter

Abstract

High precision time-of-flight (TOF) measurements in modern high-energy physics experiments have often a high demand to measure both pulse timing and pulse width at the same time. The pulse width from such TOF detectors can be as narrow as 1 ns, which poses great challenges to current design of time-to-digital converters (TDCs) based on field programmable gate array (FPGA). In this paper, we propose a novel FPGA-based TDC design which can measure nuclear signals with extremely narrow pulse width outputting timestamps for both the rising edge and falling edge simultaneously. The discriminated digital signal with both timings from the rising edge and falling edge is directly transmitted along the tapped-delay-line (TDL) of the TDC. Relying on the proposed powerful and efficient encoding logic, the two timestamps are precisely extracted out from the TDL status in one time of measurement. The TDC measurement dead time is only two system clock cycle, and the minimum measurable pulse width is only limited by the performance of LVDS receiver of FPGA, which was tested as low as 400 ps in our case of implementing the TDC in a Virtex Ultrascale+ FPGA. Using one TDC channels to measure given pulse width, the RMS precision is evaluated as 3.0 ps. Given the pulse widths ranging from 0.4 ns to 1.5 ns, the measured pulse width by the TDC is highly consistent with the readout values from the oscilloscope. In addition to the excellent performance, compared with previous TDC designs for pulse width measurement, the structure of the proposed TDC is much compact with low logic resource consumption, which is very helpful for multi-channel integration in high-energy physics experiments.