Periodical correlation detection for background light suppression in direct time-of-flight sensor

A system for time-of-flight (TOF) sensing, comprising:

• a sensing module array comprising a plurality of sensing modules, each of the sensing modules comprising:
• a plurality of single-photon avalanche diode (SPAD) cells for receiving reflected light pulses, wherein each of the SPAD cells outputs a pixel event signal with logical high if the SPAD cell receives a reflected light pulse, and wherein one of the SPAD cells is a selected SPAD cell;
• a periodical correlation detection (PCD) circuit, wherein the PCD circuit counts the pixel event signals with logical high for each detection period, wherein the PCD circuit further comprises a timestamp counter for outputting a timestamp signal, wherein the timestamp signal is reset at the beginning of each repeated cycle;
• a timestamp data comparator configured to store and compare timestamp signals, wherein the PCD circuit operates in either a first operating mode or a second operating mode based on an output of the timestamp data comparator (Deq);
• a time-to-digital converter (TDC) configured to output TDC data when the TDC is valid.

A method for time-of-flight sensing, the method comprising:

• selecting a single-photon avalanche diode (SPAD) cell of a plurality of SPAD cells for receiving reflected light pulses;
• counting the number of the SPAD cells of the plurality of SPAD cells that receive the reflected light pulses for a detection period;
• determining whether the number of the SPAD cells that receive the reflected light pulses reach a predetermined threshold in the detection period;
• determining whether the selected SPAD cell receives the reflected light pulses in the detection period;
• and
• if the number of the SPAD cells that receive the reflected light pulses in the detection period reach a predetermined threshold and if the selected SPAD cell receives the reflected light pulses in the detection period, recording a timestamp of the detection period and outputting time-to-digital converter (TDC) data.