Time-to-digital converter with an analog interpolation circuit

The construction and capability of a time-to-digital converter (TDC) is presented. The TDC consists of a 100-MHz clock and an analog interpolation circuit composed of two time-to-amplitude converters for the time fractions between the start pulse and the next clock pulse but one and the stop pulse and the next clock pulse but one, respectively. The difference between the time fractions is digitized with an analog-to-digital converter, and the output of this plus the main counters roughly digitizing the time interval to be measured are then summed to give the final result. The channel width, single-shot accuracy, and measurement range of the TDC are about 40 ps, 80 ps (FWHM), and 2.5 μs, respectively. The effects of the averaging of the measurement results on the resolution and accuracy of the device are measured and discussed. The temperature stability of the interpolation circuit is better than 3 ps/°C. The TDC combines the good single-shot accuracy of time-to-amplitude conversion with the long measurement range of the direct counting method and is thus believed to be well suited for time-of-flight laser range-finding measurements in industrial applications.