Time-to-Digital Converter With 2.1-ps RMS Single-Shot Precision and Subpicosecond Long-Term and Temperature Stability

This paper presents the design and performance measurement results of a prototype time-to-digital converter (TDC) implemented using commercially available components. The TDC is based on an interpolation principle. In this principle, the time interval is first roughly digitized by a coarse counter driven by a high-stability reference clock, and the fractions between the clock periods are measured by two high-resolution interpolators based on the time-to-amplitude conversion method. This principle ensures theoretically unlimited measurement range with fine time resolution. The TDC achieves 2.1-ps rms time interval measurement precision with a resolution of 0.17 ps and the maximum measurement rate of 200 Hz. The estimated single-channel precision is 1.5-ps rms. A unique circuit structure was developed to allow individual channel calibration after each event. During the calibration, a value corresponding to one reference clock period is obtained. This gives the TDC an outstanding long-term stability of 110 fs peak-peak and a long-term drift of 0.2 fs/h over a 24-h interval. The calibration also helps to obtain a high temperature stability of 0.2 ps/°C. The power consumption is 10 W. The circuit structure allows for programmable customization of the TDC to satisfy many potential applications in time-of-flight systems, such as laser range finding or event counting.