CMOS Time-Domain Imager for Functional Brain Imaging Using Gated Near-Infrared Spectroscopy
The main challenges in designing a TD NIRSI sensor deal with four issues: spectral responsivity, noise, fill-factor, and throughput. The spectral responsivity and noise are shaped by the technology process and structure (see figure 2) of the SPAD. The fill-factor is determined by the ancillary circuitry needed to maintain the TD operation of the SPAD (i.e., frontend, gating, and TDC). The throughput is dependent on the readout architecture of the array of pixels.
We are proposing a fully integrated scalable array of time-gated actively-quenched SPADs with shared time-gated ring-oscillator-based TDCs following H-tree-based architecture and a 3-transistor active-pixel sensor (3T APS) readout scheme with in-pixel storage capability to be implemented using standard deep sub-micron CMOS technology. For example, using 130 nm CMOS technology SPADs can be built with an area of 50 um2 which exhibit a dark count rate (DCR) of 18 KHz. At a wavelength around 600 nm and an excess bias of 2 V, their photon detection probability (PDP) could reach 22%. These SPADs breakdown at 20 V and could resolve down to 90 ps for wavelengths around 654 nm. With the same technology a 0.04 mm2 TDC can be designed with a resolution or least significant bit (LSB) of 6 ps for a range of 11-bits. Moreover, SPAD structure variations, novel gating schemes, smart resource sharing, and efficient array architecture a CMOS TD NIRSI sensor can be realized to meet requirements of functional human brain imaging applications.
 A. Torricelli, D. Contini, A. Pifferi, M. Caffini, R. Re, L. Zucchelli and L. Spinelli, "Time domain functional NIRS imaging for human brain mapping," J NeuroImage, 2013.
 E. Villella, O. Alonso, A. V. A. Montiel and A. Dieguez, "A low-noise time-gated single-photon detector in HV-CMOS technology for triggered imaging," Sensors and Actuators A: Physical, vol. 201, p. 342, 2013.
 C. Niclass, M. Soga, H. Matsubara, M. Ogawa and M. Kagami, "A 0.18-um CMOS SoC for a 100-nm-Range 10-Frame/s 200 x 96-Pixel Time-of-Flight Depth Sensor," IEEE Journal of Solid-State Circuits, vol. 49, no. 1, 2014.
 D. Palubiak, M. El-Desouki, O. Marinov, M. J. Deen and Q. Fang, "High-Speed, Single-Photon Avalanche-Photodiode Imager for Biomedical Applications," IEEE Sensors Journal, vol. 11, no. 10, p. 2401, 2011.
 E. Webster, L. Grant and R. Henderson, "A High-Performance Single-Photon Avalanche Diode in 130-nm CMOS Imaging Technology," IEEE Electron Device Letters, vol. 33, no. 11, p. 1589, 2012.
 M. Straayer and M. Perrott, "A multi-path gated ring oscillator TDC with first-order noise shaping," IEEE Journal of Solid-State Circuits, vol. 44, no. 4, p. 1089, 2009.
 M. Ferrari and V. Quaresima, "A brief review on the history of human functional near-infrared spectroscopy (fNIRS) development and fields of application," J NeuroImage, vol. 63, p. 921, 2012.
 L. Braga, L. Gasparini, L. Grant, R. Henderson, N. Massari, M. Perenzoni, D. Stoppa and R. Walker, "A Fully Digital 8 x 16 SiPM Array for PET Applications With Per-Pixel TDCs and Real-Time Energy Output," IEEE Journal of Solid-State Circuits, vol. 49, no. 1, 2014.