A 4x4 region of interest is about the limit. Each photon strike needs a quench cycle to reset the detector. Any fewer than 16 and it would take forever to get enough photons to get a measurement.
So, alas, 4x4 is the minimum.
It also insures there is enough flexibility for the sensor to adjust the SPADs (detectors.) Not all of them are the same.
- john
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I am a recently retired ST Employee. My former username was John E KVAM.
