This application relates to a
code density calibration method and
system based on dark counting. The method includes: setting a SPAD in Geiger mode under no-light conditions; generating a Poisson-distributed dark counting pulse unrelated to the TDC
clock using thermal perturbation; using this pulse as a trigger
signal to acquire and convert raw code during non-measurement periods /
independent channels; recording the frequency of each unit using a counter array; calculating the total number of samples and the
system period; calculating the calibration results of each unit, as well as differential and integral nonlinear indices; calculating the correction time value based on the indices; storing the calibration time in on-
chip storage using the raw code as an index; constructing a calibration
lookup table; during actual detection, using the raw code to address and look up the table, reading the calibration time and combining it with the coarse count to synthesize a high-precision result. This method can improve the measurement accuracy, stability, and environmental adaptability of a high-precision time-to-
digital converter.