Patent ID: 6384663
Filing Date: 2002-05-07
Classification: G01J

Abstract:
Quenching and output circuit for a SPAD type photodiode suitable for producing a signal with a risetime of the leading edge almost as rapid as the intrinsic risetime of the avalanche current pulse within the SPAD, therefore in a time range from a few tens of picoseconds to some nanoseconds, and having a total duration in a time range from some nanoseconds to some tens of nanoseconds, said circuit comprising a comparator for detecting the avalanche pulse that has the input connected to an output point of a circuit block of coupling in alternate current, that has its input connected to a first terminal of the SPAD photodiode biased at high voltage, and means placed between ground and a second terminal of said SPAD for quenching the avalanche and taking out and counting signals, characterized in that the circuit elements present in said circuit block are such that they determine a filtering action which towards high frequencies shows a low-pass type frequency cut-off, with characteristic cut-off frequency preferably corresponding to a simple pole, that is to a simple integration time constant, and towards low frequencies a high-pass cut-off, with characteristic cut-off frequency preferably corresponding to a simple pole, that is to a simple differentiation time constant, and in that the values of the circuit parameters are selected so that the value of said high-pass cut-off frequency is less than said low-pass cut-off frequency and less than the bandwidth limit of the avalanche current pulse, but is greater than the value determined by the reciprocal of the duration of said pulse, that is that said differentiation time constant is greater than that of the integration and of the risetime of the avalanche current pulse, but is less than the duration of said pulse.