On the time gating of SPADs in a synchronized time-gated SPAD array in Raman spectroscopy

The effect of the timing of the biasing of a single photon avalanche diode (SPAD) on the accuracy of a time-gated SPAD array has been studied in this work. The measurement was realized in a time-gated Raman spectrometer utilizing a 16×256 CMOS SPAD array with on-chip time gating electronics. SPADs have to be biased into the Geiger-mode just before arriving Raman scattered photons from the sample to achieve synchronous measurements with a pulsed laser, and to minimize the dark count noise. The practical realization is, however, not straight-forward due to the strict timing requirements (~50ps). With the shown biasing arrangement high timing accuracy and low noise can be achieved without sacrificing the fill factor of the detector array.