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Fluorescence lifetime detection is widely used in molecular biology to monitor many cell parameters (such as pH, ion
concentrations, etc.) and for an early diagnosis of many pathologies. In a typical fluorescence lifetime experiment a
pulsed laser is used to excite the fluorescent dyes and the emitted light is revealed by means of high sensitivity detectors,
typically: intensified CCD, PMTs or Single-Photon Avalanche Diodes (SPADs).In this contribute we present a SPAD
detector module fabricated in a 0.35μm High Voltage CMOS technology to be used within a lab-on-chip system
consisting of a micro-reactor array for bioaffinity assays based on fluorescence markers. The detector module, having a
total area of 600 x 900 μm2, can be arranged to build a small pixel array to be directly coupled to the micro-reactors. No
emission filters are needed, since the ultra-short laser pulse is cut off in the time domain. The module consists of a
10x10-SPAD array, where each SPAD cell is equipped with dedicated active quenching and recharging circuit. Each cell
has a pitch of 26μm with a fill factor of 48%. The SPADs have been binned in order to realize a large photosensitive area
detector exhibiting a reasonably low dark count rate (DCR) and reduced dead time, as required in a fast measurement
system. A memory has also been implemented in order to enable only low DCR SPADs, so that a total DCR of about
100kHz can be achieved for the whole photosensitive area. The digital output generated by the SPAD array is sent to a
time-discriminator stage which allows a time-gated detection of the incident light. Two time-windows have been
implemented in this architecture. Their time width is controlled by an on-chip digital PLL locked to the external laser
clock whereas the width of the time-windows can be set within the range 500ps-10ns with a resolution of 500ps. Photons
detected within each time window are then counted by two 10-bits digital counters. Time-interleaved operation has been
implemented to read out the pixel data in parallel with the photon detection phase.
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