Abstract-We introduce the first integrated active quenching circuit (I-AQC) that drives an avalanche photodiode (APD) above its breakdown voltage, in order to detect single photons. Based on the I-AQC, we developed a compact and versatile photon-counting module suitable for applications in which very weak optical signals have to be detected, as for instance, photon correlation spectroscopy, luminescence measurements, and laser ranging. The prototype photon-counting module features quenching pulses up to 60 V amplitude, minimum dead time of less than 36 ns, corresponding to a saturated counting rate exceeding 25 Mcounts/s, user-controllable hold-off time, for reducing the afterpulsing effect, and nanosecond gating capability. The power dissipation is 60 mW in stand-by conditions, and the module size is less than 1 cm 2 cm. Index Terms-Active-quenching circuit (AQC), application specific integrated circuit (ASIC), avalanche photodiode (APD), photo detection module, photon counting, single-photon avalanche diode (SPAD), single-photon detection. Photo Multiplier Tubes (PMTs) [22] ; the absence of read-out noise, and the possibility of fast parallel read-out, make an array of APD more suitable than CCDs in many applications, such as adaptive optics [20] . Moreover APDs can be easily switched on and off with nanosecond transitions, which allow the detector to be gated by suitable electronics, synchronised to the optical excitation. For single-photon detection, the APD can be operated either in the analog-multiplying regime, biased close to but below the breakdown voltage, or in the so-called Geiger-mode, above breakdown. In this paper, we will deal only with the latter regime, where a proper electronic circuit biases the APD above breakdown voltage and quickly quenches the avalanche current, as soon as a diverging multiplication process is triggered, e.g., due to the absorption of a single photon in the visible and near-infrared wavelength range [23] . In the literature, an APD operated in the Geiger-mode is known as single-photon avalanche diode (SPAD). The duration of the SPADs avalanche current must be as short as possible for three main reasons: 1) self-heating; 2) trapping; and 3) optical cross talk. These are discussed in further detail below. 1) Excessive power dissipation leads to the heating of the diode and the shift of its breakdown voltage [24] . The latter effect causes a change in the quantum efficiency of the detector, thus introducing severe nonlinear distortion in photon counting. 2) Carriers participating to the avalanche current can be trapped near the junction and are subsequently released, thus re-triggering the APD [23] . This correlated after pulse, which causes nonlinear distortion in the counting, can be reduced by minimizing the total number of carriers crossing the junction during the avalanche, that is, its intensity and its duration. 3) Avalanche hot-carriers emit secondary photons due to Bremsstrahlung and radiative relaxations [25] . These photons can be absorbed in neighboring SPADs, thus triggering a spurious avalanche therein. Such optical cross talk is of primary importance in a monolithic array of SPADs, if a suitable optical isolation among the diodes is not employed [26] , [27] . A simple way to self-limit the avalanche current is to place a high-value resistor in series to the SPAD, thus setting up a so-called passive quenching [23] . The advantage of such a configuration is that the avalanche is quickly self-quenched within a few nanoseconds, but at the expense of a slow recovery transition, in the microsecond range, due to stray capacitances [23] .
The first work focusing on the simulation of SPAD detectors REF ] models the electronics of an active quenched circuit.
An integrated active-quenching circuit for single-photon avalanche diodes
IEEE Trans. Instrumentation and Measurement
IEEE Trans. Instrumentation and Measurement
Physics Computer Science