A 7.9 ps Resolution, Multi-Event TDC Using an Ultra-Low Static Phase Error DLL and High Linearity Time Amplifier for dToF Sensors

SPAD-based dToF sensors employ Time-Correlated Single Photon Counting (TCSPC) to accurately determine the ToF information. The multi-event time-to-digital converter (TDC) with low dead time is crucial to mitigate the pile-up distortion. Similarly, linear-mode dToF sensors pay more attention to the TDC resolution. A histogramming TDC [1] has achieved a conversion rate of 14 GS/s, but its resolution is limited by the gate delay. A multi-event TDC with a conversion rate of 50 MS/s is presented in [2]. The linearity performance is deteriorated due to only one interpolator used, and the resolution is insufficient for near targets. A high resolution TDC is proposed in [3] utilizing a calibration-free time amplifier (TA), whereas only one photon event can be quantified during a laser cycle. The multi-event scheme can also be achieved by interleaving operation [4], [5], but the maximum events number is limited by TDC channels. In this paper, a multi-event TDC is proposed with high conversion rate and unlimited event number using an interpolator recycling technique. A high resolution is realized by a coarse-fine interpolation with a high linearity TA, and an ultra-low static phase error (SPE) DLL is proposed to improve the TDC linearity. The proposed TDC achieves a 7.9 ps resolution over 2033.5 ns dynamic range with a conversion rate of 80 MS/s.