Characterization of the Timing Homogeneity in a CMOS SPAD Array Designed for Time-Gated Raman Spectroscopy

A characterization environment was built to verify the timing characteristics of a single photon avalanche diode (SPAD) array designed for time-gated Raman spectroscopy. The characterization was applied to a 256 x 16 SPAD array that employed an on-chip time-to-digital converter (TDC) with a 50-100-ps resolution for time resolving. The timing skew and the time window homogeneity across the array were resolved, moving the time-resolving windows over an optical pulse by picosecond-level delay steps. A typical one 160-ps skew across the array was measured. The TDC time bins had average sizes of 33-144 ps while their deviation across the array was 8-12 ps. The method is applicable to multidetector time-correlated single photon counting systems that can finely adjust the delay between the optical pulse and the reference signal.