An 18-ps TDC using timing adjustment and bin realignment methods in a Cyclone-IV FPGA

The method commonly used to produce a field-programmable gate array (FPGA)-based time-to-digital converter (TDC) creates a tapped delay line (TDL) for time interpolation to yield high time precision. We conduct timing adjustment and bin realignment to implement a TDC in the Altera Cyclone-IV FPGA. The former tunes the carry look-up table (LUT) cell delay by changing the LUT's function through low-level primitives according to timing analysis results, while the latter realigns bins according to the timing result obtained by timing adjustment so as to create a uniform TDL with bins of equivalent width. The differential nonlinearity and time resolution can be improved by realigning the bins. After calibration, the TDC has a 18 ps root-mean-square timing resolution and a 45 ps least-significant bit resolution.