Large-Area, Fast-Gated Digital SiPM With Integrated TDC for Portable and Wearable Time-Domain NIRS
Enrico Conca, Vincenzo Sesta, Mauro Buttafava, Federica Villa, Laura Di Sieno, Alberto Dalla Mora, Davide Contini, Paola Taroni, Alessandro Torricelli, Antonio Pifferi, Franco Zappa, Alberto Tosi
Abstract
We present the design and characterization of a large-area, fast-gated, all-digital single-photon detector with programmable active area, internal gate generator, and time-todigital converter (TDC) with a built-in histogram builder circuit, suitable for performing high-sensitivity time-domain nearinfrared spectroscopy (TD-NIRS) measurements when coupled with pulsed laser sources. We used a novel low-power differential sensing technique that optimizes area occupation. The photodetector is a time-gated digital silicon photomultiplier (dSiPM) with an 8.6-mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> photosensitive area, 37% fill-factor, and ~300 ps (20%-80%) gate rising edge, based on low-noise single-photon avalanche diodes (SPADs) and fabricated in 0.35-μm CMOS technology. The built-in TDC with a histogram builder has a least-significant-bit (LSB) of 78 ps and 128 time-bins, and the integrated circuit can be interfaced directly with a low-cost microcontroller with a serial interface for programming and readout. Experimental characterization demonstrated a temporal response as good as 300-ps full-width at half-maximum (FWHM) and a dynamic range >100 dB (thanks to the programmable active area size). This microelectronic detector paves the way for a miniaturized, stand-alone, multi-wavelength TD-NIRS system with an unprecedented level of integration and responsivity, suitable for portable and wearable systems.