Towards low-timing jitter photon number-resolved digital silicon photomultipliers

An innovative general-purpose Digital Silicon-PhotoMultiplier (dSiPM) with 32 x 32 SPADs, designed in 160 nm BCD technology, is presented. The main goals of this device are to enhance the dynamic range, still keeping the single-photon resolution, and minimize the timing jitter. Both an analog and a digital approach are used to distinguish between 1 to similar to 300 incoming photons. A voltage-controlled current generator converts the pixel's digital output pulse in a current pulse, tunable in amplitude (10 mu A divided by 350 mu A) and duration (from 1 ns to the SPAD holdoff time). The digital option is useful in low photon flux applications. Instead, in high photon flux applications, the digital output misses information, due to an overlap among the photon pulses, so the analog option is to be preferred. Moreover, a double threshold algorithm is implemented in order to reduce the timing jitter of the output. Basically, the concept behind this procedure is to refer the timing measurement to the crossing of the lower threshold, while the higher threshold is only used as a validation for the measurement. Finally, a Time-to-Digital Converter (TDC), with a resolution of 75 ps, is integrated to provide the timing information. The SPAD frontend design works in a free running photon detection modality, and there is the possibility to enable or disable the pixels individually. Thanks to its programmable number of photon resolution and the improved timing performance, the detector can be exploited in many different scientific applications.