3D imaging; 3DIC; CMOS imager; Direct Time-of-Flight (dToF); Depth image sensors; Indirect Time-of-Flight (iToF); Light Detection and Ranging (LiDAR); Time-of-Flight (ToF); Single-Photon Avalanche Diode (SPAD)
Abstract :
[en] Time-of-flight (ToF) sensors using light pulses or continuous waves allow accurate distance measurements. Three-dimensional imagers can be based on an array of timing or time-gated integration pixels. Single-photon avalanche diodes (SPADs) have been increasingly chosen as the pixel’s photodetector device to develop fast, long-range ToF sensors. Solid-state ToF cameras are replacing other alternatives, showing attractive characteristics and bringing up new potential applications. This paper presents the technical evolution of SPAD ToF 3D imaging sensors, and provides insight into their development over the last few decades. Starting with the first SPAD imagers reported in the early 2000’s, various direct and indirect arrays up to present day state-of-the-art prototypes are referenced. The existing methods, options and possible implementations are described, addressing their advantages and drawbacks, and showing the progress yet to be made. The performance of the different presented approaches are given and compared.
Research Center/Unit :
Montefiore Institute - Montefiore Institute of Electrical Engineering and Computer Science - ULiège
Disciplines :
Electrical & electronics engineering
Author, co-author :
Piron, François ✱; Université de Liège - ULiège > Dép. d'électric., électron. et informat. (Inst.Montefiore) > Systèmes microélectroniques intégrés
Morrison, Daniel ✱; Monash University > Department of Electrical and Computer Systems Engineering
Yuce, Mehmet Rasit; Monash University > Department of Electrical and Computer Systems Engineering
Redouté, Jean-Michel ; Université de Liège - ULiège > Dép. d'électric., électron. et informat. (Inst.Montefiore) > Systèmes microélectroniques intégrés
✱ These authors have contributed equally to this work.
Language :
English
Title :
A Review of Single-Photon Avalanche Diode Time-of-Flight Imaging Sensor Arrays
Publication date :
2021
Journal title :
IEEE Sensors Journal
ISSN :
1530-437X
eISSN :
1558-1748
Publisher :
Institute of Electrical and Electronics Engineers, New York, United States - New York
F. Blais, "Review of 20 years of range sensor development, " J. Electron. Imag., vol. 13, no. 1, pp. 231-243, 2004.
T. Spirig, P. Seitz, O. Vietze, F. Heitger, "The lock-in CCD-twodimensional synchronous detection of light, " IEEE J. Quantum Electron., vol. 31, no. 9, pp. 1705-1708, 1995.
S. Foix, G. Alenya, C. Torras, "Lock-in time-of-flight (ToF) cameras: A survey, " IEEE Sensors J., vol. 11, no. 9, pp. 1917-1926, Sep. 2011.
M. Hansard, S. Lee, O. Choi, R. P. Horaud, Time-of-Flight Cameras: Principles, Methods and Applications. Cham, Switzerland: Springer, 2012.
R. Horaud, M. Hansard, G. Evangelidis, C. Ménier, "An overview of depth cameras and range scanners based on time-of-flight technologies, " Mach. Vis. Appl., vol. 27, no. 7, pp. 1005-1020, Oct. 2016.
S. Cova, A. Lacaita, G. Ripamonti, "Trapping phenomena in avalanche photodiodes on nanosecond scale, " IEEE Electron Device Lett., vol. 12, no. 12, pp. 685-687, Dec. 1991.
F. Remondino and D. Stoppa, TOF Range-Imaging Cameras. Berlin, Germany: Springer-Verlag, Jul. 2013.
S. Cova, A. Longoni, A. Andreoni, "Towards picosecond resolution with single-photon avalanche diodes, " Rev. Sci. Instrum., vol. 52, no. 3, pp. 408-412, Mar. 1981.
S. Cova, A. Longoni, A. Andreoni, R. Cubeddu, "A semiconductor detector for measuring ultraweak fluorescence decays with 70 ps FWHM resolution, " IEEE J. Quantum Electron., vol. 19, no. 4, pp. 630-634, Apr. 1983.
R. J. McIntyre, "Recent developments in silicon avalanche photodiodes, " Measurement, vol. 3, no. 4, pp. 146-152, Oct. 1985.
B. F. Aull, A. H. Loomis, J. A. Gregory, D. J. Young, "Geiger-mode avalanche photodiode arrays integrated with CMOS timing circuits, " in 56th Annu. Device Res. Conf. Dig., Jun. 1998, pp. 58-59.
B. F. Aull, et al., "Geiger-mode avalanche photodiodes for three-dimensional imaging, " Lincoln Lab. J., vol. 13, no. 2, pp. 335-349, 2002.
A. Rochas, et al., "Single photon detector fabricated in a complementary metal-oxide-semiconductor high-voltage technology, " Rev. Sci. Instrum., vol. 74, no. 7, pp. 3263-3270, Jul. 2003.
D. P. Palubiak and M. J. Deen, "CMOS SPADs: Design issues and research challenges for detectors, circuits, arrays, " IEEE J. Sel. Topics Quantum Electron., vol. 20, no. 6, pp. 409-426, Nov. 2014.
C. Bruschini, H. Homulle, E. Charbon, "Ten years of biophotonics single-photon SPAD imager applications: Retrospective and outlook, " Proc. SPIE, vol. 10069, pp. 213-233, Feb. 2017.
X. Ren, et al., "High-resolution depth profiling using a range-gated CMOS SPAD quanta image sensor, " Opt. Express, vol. 26, no. 5, pp. 5541-5557, Mar. 2018.
I. Gyongy, et al., "A 256 × 256, 100-kfps, 61% fill-factor SPAD image sensor for time-resolved microscopy applications, " IEEE Trans. Electron Devices, vol. 65, no. 2, pp. 547-554, Feb. 2018.
C. Niclass, A. Rochas, P.-A. Besse, E. Charbon, "Toward a 3-D camera based on single photon avalanche diodes, " IEEE J. Sel. Topics Quantum Electron., vol. 10, no. 4, pp. 796-802, Jul. 2004.
F. Villa, et al., "CMOS imager with 1024 SPADs and TDCs for single-photon timing and 3-D time-of-flight, " IEEE J. Sel. Topics Quantum Electron., vol. 20, no. 6, pp. 364-373, Nov. 2014.
A. Rochas, et al., "First fully integrated 2-D array of single-photon detectors in standard CMOS technology, " IEEE Photon. Technol. Lett., vol. 15, no. 7, pp. 963-965, Jul. 2003.
ST Microelectronics. Vl53l5 Data Brief. Accessed: Nov. 5, 2020. [Online]. Available: Https://www.st.com/resource/en/databrief/vl53l5.pdf
C. Niclass, A. Rochas, P.-A. Besse, E. Charbon, "Design and characterization of a CMOS 3-D image sensor based on single photon avalanche diodes, " IEEE J. Solid-State Circuits, vol. 40, no. 9, pp. 1847-1854, Sep. 2005.
C. Niclass, C. Favi, T. Kluter, M. Gersbach, E. Charbon, "A 128×128 single-photon image sensor with column-level 10-bit timeto-digital converter array, " IEEE J. Solid-State Circuits, vol. 43, no. 12, pp. 2977-2989, Dec. 2008.
D. Stoppa, et al., "A 32×32-pixel array with in-pixel photon counting and arrival time measurement in the analog domain, " in Proc. ESSCIRC, Sep. 2009, pp. 204-207.
C. Veerappan, et al., "A 160×128 single-photon image sensor with on-pixel 55ps 10b time-to-digital converter, " in Proc. IEEE Int. Solid-State Circuits Conf., Feb. 2011, pp. 312-314.
B. Markovic, S. Tisa, A. Tosi, F. Zappa, "Smart-pixel for 3D ranging imagers based on single-photon avalanche diode and time-todigital converter, " in Proc. Adv. Photon Counting Techn. V, vol. 8033, May 2011. Art. no. 80330A.
F. Villa, et al., "SPAD smart pixel for time-of-flight and time-correlated single-photon counting measurements, " IEEE Photon. J., vol. 4, no. 3, pp. 795-804, Jun. 2012.
I. Vornicu, R. Carmona-Galán, A. Rodríguez-Vázquez, "A SPAD-based 3D imager with in-pixel TDC for 145ps-accuracy ToF measurement, " Proc. SPIE, vol. 9403, Mar. 2015, Art. no. 94030I.
J. M. Pavia, M. Scandini, S. Lindner, M. Wolf, E. Charbon, "A 1×400 backside-illuminated SPAD sensor with 49.7 ps resolution, 30 pJ/sample TDCs fabricated in 3D CMOS technology for near-infrared optical tomography, " IEEE J. Solid-State Circuits, vol. 50, no. 10, pp. 2406-2418, Oct. 2015.
N. Roy, F. Nolet, F. Dubois, M.-O. Mercier, R. Fontaine, J.-F. Pratte, "Low power and small area, 6.9 ps RMS time-to-digital converter for 3-D digital SiPM, " IEEE Trans. Radiat. Plasma Med. Sci., vol. 1, no. 6, pp. 486-494, Nov. 2017.
A. R. Ximenes, P. Padmanabhan, M.-J. Lee, Y. Yamashita, D. N. Yaung, E. Charbon, "A 256×256 45/65nm 3D-stacked SPAD-based direct TOF image sensor for LiDAR applications with optical polar modulation for up to 18.6dB interference suppression, " in IEEE Int. Solid-State Circuits Conf. (ISSCC) Dig. Tech. Papers, Feb. 2018, pp. 96-98.
S. W. Hutchings, et al., "A reconfigurable 3-D-stacked SPAD imager with in-pixel histogramming for flash LIDAR or high-speed time-of-flight imaging, " IEEE J. Solid-State Circuits, vol. 54, no. 11, pp. 2947-2956, Nov. 2019.
F. Nolet, et al., "A 256 pixelated SPAD readout ASIC with in-pixel TDC and embedded digital signal processing for uniformity and skew correction, " Nucl. Instrum. Methods Phys. Res. A, Accel. Spectrom. Detect. Assoc. Equip., vol. 949, Jan. 2020, Art. no. 162891.
G. Intermite, et al., "Enhancing the fill-factor of CMOS SPAD arrays using microlens integration, " Proc. SPIE, vol. 9504, May 2015, Art. no. 95040J.
R. K. Henderson, et al., "A 192×128 time correlated SPAD image sensor in 40-nm CMOS technology, " IEEE J. Solid-State Circuits, vol. 54, no. 7, pp. 1907-1916, Jul. 2019.
T. Frach, G. Prescher, C. Degenhardt, R. de Gruyter, A. Schmitz, R. Ballizany, "The digital silicon photomultiplier-principle of operation and intrinsic detector performance, " in Proc. IEEE Nucl. Sci. Symp. Conf. Rec. (NSS/MIC), Oct. 2009, pp. 1959-1965.
T. Frach, G. Prescher, C. Degenhardt, B. Zwaans, "The digital silicon photomultiplier-system architecture and performance evaluation, " in Proc. IEEE Nucl. Sci. Symp. Med. Imag. Conf., Oct. 2010, pp. 1722-1727.
L. H. C. Braga, et al., "A CMOS mini-SiPM detector with in-pixel data compression for PET applications, " in Proc. IEEE Nucl. Sci. Symp. Conf. Rec., Oct. 2011, pp. 548-552.
L. H. C. Braga, et al., "A fully digital 8×16 SiPM array for PET applications with per-pixel TDCs and real-time energy output, " IEEE J. Solid-State Circuits, vol. 49, no. 1, pp. 301-314, Jan. 2014.
S. Mandai and E. Charbon, "A 4×4×416 digital SiPM array with 192 TDCs for multiple high-resolution timestamp acquisition, " J. Instrum., vol. 8, no. 5, May 2013, Art. no. P05024.
A. Carimatto, et al., "A 67, 392-SPAD PVTB-compensated multi-channel digital SiPM with 432 column-parallel 48ps 17b TDCs for endoscopic time-of-flight PET, " in IEEE Int. Solid-State Circuits Conf. (ISSCC) Dig. Tech. Papers, Feb. 2015, pp. 1-3.
M. Perenzoni, D. Perenzoni, D. Stoppa, "A 64 × 64-pixels digital silicon photomultiplier direct TOF sensor with 100-MPhotons/s/pixel background rejection and imaging/altimeter mode with 0.14% precision up to 6 km for spacecraft navigation and landing, " IEEE J. Solid-State Circuits, vol. 52, no. 1, pp. 151-160, Jan. 2017
E. Manuzzato, et al., "A 16×8 digital-SiPM array with distributed trigger generator for low SNR particle tracking, " in Proc. 45th IEEE Eur. Solid-State Circuits Conf., Sep. 2019, pp. 75-78.
E. Conca, et al., "Large-area, fast-gated digital SiPM with integrated TDC for portable and wearable time-domain NIRS, " IEEE J. Solid-State Circuits, vol. 55, no. 11, pp. 3097-3111, Nov. 2020.
J.-P. Jansson, S. Jahromi, K. Haapalainen, H. Juttula, A. Makynen, J. Nissinen, "An integrated 9×9 SPAD array with a 10-channel TDC and a CMOS laser diode driver for a wearable time-domain diffuse optics optode, " in Proc. IEEE Int. Instrum. Meas. Technol. Conf. (I2MTC), May 2020, pp. 1-5.
C. Niclass, M. Soga, H. Matsubara, S. Kato, M. Kagami, "A 100-m range 10-frame/s 340×96-pixel time-of-flight depth sensor in 0.18-?m CMOS, " IEEE J. Solid-State Circuits, vol. 48, no. 2, pp. 559-572, Feb. 2013.
Y. M. Wang, L. Shi, C. Wang, K. O. Kim, I. Ovsiannikov, S. Hwang, "A direct TOF sensor with in-pixel differential time-to-charge converters for automotive flash Lidar and other 3D applications, " in Proc. Int. Image Sens. Workshop, Jun. 2019, p. R24.
D. Morrison, D. Delic, M. R. Yuce, J.-M. Redoute, "Multistage linear feedback shift register counters with reduced decoding logic in 130-nm CMOS for large-scale array applications, " IEEE Trans. Very Large Scale Integr. (VLSI) Syst., vol. 27, no. 1, pp. 103-115, Jan. 2019.
I. Nissinen, A. Mantyniemi, J. Kostamovaara, "A CMOS timeto-digital converter based on a ring oscillator for a laser radar, " in Proc. 29th Eur. Solid-State Circuits Conf. (ESSCIRC), 2003, pp. 469-472.
J. Nissinen, I. Nissinen, J. Kostamovaara, "Integrated receiver including both receiver channel and TDC for a pulsed time-of-flight laser rangefinder with cm-level accuracy, " IEEE J. Solid-State Circuits, vol. 44, no. 5, pp. 1486-1497, May 2009.
J. Richardson, et al., "A 32×32 50ps resolution 10 bit time to digital converter array in 130nm CMOS for time correlated imaging, " in Proc. IEEE Custom Integr. Circuits Conf., Sep. 2009, pp. 2819-2830.
C. Zhang, S. Lindner, I. M. Antolovic, J. Mata Pavia, M. Wolf, E. Charbon, "A 30-frames/s, 252 × 144 SPAD flash LiDAR with 1728 dual-clock 48.8-ps TDCs, pixel-wise integrated histogramming, " IEEE J. Solid-State Circuits, vol. 54, no. 4, pp. 1137-1151, Apr. 2019.
M. Zarghami, et al., "A 32×32-pixel CMOS imager for quantum optics with per-SPAD TDC, 19.48% fill-factor in a 44.64-?m pitch reaching 1-MHz observation rate, " IEEE J. Solid-State Circuits, vol. 55, no. 10, pp. 2819-2830, Oct. 2020.
Z. Cheng, X. Zheng, M. J. Deen, H. Peng, "Recent developments and design challenges of high-performance ring oscillator CMOS timeto-digital converters, " IEEE Trans. Electron Devices, vol. 63, no. 1, pp. 235-251, Jan. 2016.
B. Markovic, S. Tisa, F. A. Villa, A. Tosi, F. Zappa, "A high-linearity, 17 ps precision time-to-digital converter based on a single-stage Vernier delay loop fine interpolation, " IEEE Trans. Circuits Syst. I, Reg. Papers, vol. 60, no. 3, pp. 557-569, Mar. 2013.
L. Parmesan, N. A. W. Dutton, N. J. Calder, A. J. Holmes, L. A. Grant, R. K. Henderson, "A 9.8 ?m sample and hold time to amplitude converter CMOS SPAD pixel, " in Proc. 44th Eur. Solid State Device Res. Conf. (ESSDERC), Sep. 2014, pp. 290-293.
L. Parmesan, et al., "A 256×256 SPAD array with in-pixel time to amplitude conversion for fluorescence lifetime amplitude conversion for fluorescence lifetime imaging microscopy, " in Proc. Int. Image Sens. Workshop, Jun. 2015, p. M5.
S. Jahromi, J.-P. Jansson, P. Keranen, J. Kostamovaara, "A 32×128 SPAD-257 TDC receiver IC for pulsed TOF solid-state 3-D imaging, " IEEE J. Solid-State Circuits, vol. 55, no. 7, pp. 1960-1970, Jul. 2020.
D. Morrison, S. Kennedy, D. Delic, M. R. Yuce, J.-M. Redoute, "A 64×64 SPAD flash LIDAR sensor using a triple integration timing technique with 1.95 mm depth resolution, " IEEE Sensors J., early access, Oct. 13, 2020, doi: 10.1109/JSEN.2020.3030788.
G. Acconcia, M. Crotti, S. Antonioli, I. Rech, M. Ghioni, "High performance time-to-amplitude converter array, " in Proc. IEEE Nordic-Mediterranean Workshop Time-to-Digit. Converters (NoMe TDC), Oct. 2013, pp. 1-5.
T. Al Abbas, N. A. W. Dutton, O. Almer, N. Finlayson, F. M. D. Rocca, R. Henderson, "A CMOS SPAD sensor with a multi-event folded flash time-to-digital converter for ultra-fast optical transient capture, " IEEE Sensors J., vol. 18, no. 8, pp. 3163-3173, Apr. 2018.
A. T. Erdogan, R. Walker, N. Finlayson, N. Krstajic, G. O. S. Williams, R. K. Henderson, "A 16.5 giga events/s 1024×8 SPAD line sensor with per-pixel zoomable 50ps-6.4ns/bin histogramming TDC, " in Proc. Symp. VLSI Circuits, Jun. 2017, pp. C292-C293.
S. Bellisai, F. Villa, S. Tisa, D. Bronzi, F. Zappa, "Indirect time-offlight 3D ranging based on SPADs, " Proc. SPIE, vol. 8268, pp. 282-289, Jan. 2012.
A. D. Payne, A. P. Jongenelen, A. A. Dorrington, M. J. Cree, D. A. Carnegie, "Multiple frequency range imaging to remove measurement ambiguity, " in Proc. 9th Conf. Opt. 3-D Meas. Techn., Jul. 2009, pp. 139-148.
C. Niclass, C. Favi, T. Kluter, F. Monnier, E. Charbon, "Singlephoton synchronous detection, " IEEE J. Solid-State Circuits, vol. 44, no. 7, pp. 1977-1989, Jul. 2009.
M. L. Hafiane, W. Wagner, Z. Dibi, O. Manck, "Analysis and estimation of NEP and DR in CMOS TOF-3D image sensor based on MDSI, " Sens. Actuators A, Phys., vol. 169, no. 1, pp. 66-73, Sep. 2011.
S. Bellisai, D. Bronzi, F. A. Villa, S. Tisa, A. Tosi, F. Zappa, "Singlephoton pulsed-light indirect time-of-flight 3D ranging, " Opt. Express, vol. 21, no. 4, pp. 5086-5098, Feb. 2013.
F. Guerrieri, S. Tisa, A. Tosi, F. Zappa, "Two-dimensional SPAD imaging camera for photon counting, " IEEE Photon. J., vol. 2, no. 5, pp. 759-774, Oct. 2010.
R. J. Walker, J. A. Richardson, R. K. Henderson, "A 128×96 pixel event-driven phase-domain-based fully digital 3D camera in 0.13?m CMOS imaging technology, " in Proc. IEEE Int. Solid-State Circuits Conf., Feb. 2011, pp. 410-412.
D. Bronzi, et al., "100 000 frames/s 64×32 single-photon detector array for 2-D imaging and 3-D ranging, " IEEE J. Sel. Topics Quantum Electron., vol. 20, no. 6, pp. 354-363, Nov. 2014.
N. A. W. Dutton, et al., "Oversampled ITOF imaging techniques using SPAD-based quanta image sensors, " in Proc. Int. Image Sens. Workshop, Jun. 2015, pp. 170-173.
N. A. W. Dutton, et al., "A SPAD-based QVGA image sensor for single-photon counting and quanta imaging, " IEEE Trans. Electron Devices, vol. 63, no. 1, pp. 189-196, Jan. 2016.
F. Mattioli Della Rocca, et al., "A 128×128 SPAD motion-triggered time-of-flight image sensor with in-pixel histogram and column-parallel vision processor, " IEEE J. Solid-State Circuits, vol. 55, no. 7, pp. 1762-1775, Jul. 2020.
K. Morimoto, et al., "Megapixel time-gated SPAD image sensor for 2D and 3D imaging applications, " Optica, vol. 7, no. 4, pp. 346-354, Apr. 2020.
B. Park, I. Park, W. Choi, Y. Na, Y. Chae, "A 40-m range 90-frames/s CMOS time-of-flight sensor using SPAD and in-pixel time-gated pulse counter, " IEEE Solid-State Circuits Lett., vol. 3, pp. 422-425, 2020.
D. Stoppa, L. Pancheri, M. Scandiuzzo, L. Gonzo, G.-F. D. Betta, A. Simoni, "A CMOS 3-D imager based on single photon avalanche diode, " IEEE Trans. Circuits Syst. I, Reg. Papers, vol. 54, no. 1, pp. 4-12, Jan. 2007.
S. Bellisai, F. Guerrieri, S. Tisa, F. Zappa, "3D ranging with a single-photon imaging array, " Proc. SPIE, vol. 7875, pp. 152-157, Feb. 2011.
M. Perenzoni, N. Massari, D. Perenzoni, L. Gasparini, D. Stoppa, "A 160 × 120 pixel analog-counting single-photon imager with time-gating and self-referenced column-parallel A/D conversion for fluorescence lifetime imaging, " IEEE J. Solid-State Circuits, vol. 51, no. 1, pp. 155-167, Jan. 2016.
L. Pancheri, N. Massari, D. Stoppa, "SPAD image sensor with analog counting pixel for time-resolved fluorescence detection, " IEEE Trans. Electron Devices, vol. 60, no. 10, pp. 3442-3449, Oct. 2013.
T. Al Abbas, N. A. W. Dutton, O. Almer, S. Pellegrini, Y. Henrion, R. K. Henderson, "Backside illuminated SPAD image sensor with 7.83?m pitch in 3D-stacked CMOS technology, " in IEDM Tech. Dig., Dec. 2016, pp. 8.1.1-8.1.4.
T. Al Abbas, et al., "A 128×120 5-wire 1.96mm2 40nm/90nm 3D stacked SPAD time resolved image sensor SoC for microendoscopy, " in Proc. IEEE Symp. VLSI Circuits, Jun. 2019, pp. C260-C261.
E. R. Fossum, "What to do with sub-diffraction-limit (SDL) pixels?-A proposal for a gigapixel digital film sensor (DFS), " in Proc. IEEE Workshop CCDs Adv. Image Sensors, Jun. 2005, pp. 214-217.
J. Ma, D. Starkey, A. Rao, K. Odame, E. R. Fossum, "Characterization of quanta image sensor pump-gate jots with deep sub-electron read noise, " IEEE J. Electron Devices Soc., vol. 3, no. 6, pp. 472-480, Nov. 2015
S. Burri, Y. Maruyama, X. Michalet, F. Regazzoni, C. Bruschini, E. Charbon, "Architecture and applications of a high resolution gated SPAD image sensor, " Opt. Express, vol. 22, no. 14, pp. 17573-17589, Jul. 2014.
A. C. Ulku, et al., "A 512×512 SPAD image sensor with integrated gating for widefield FLIM, " IEEE J. Sel. Topics Quantum Electron., vol. 25, no. 1, pp. 1-12, Jan. 2019.
Y. Hirose, et al., "A 400×400-pixel 6?m-pitch vertical avalanche photodiodes CMOS image sensor based on 150ps-fast capacitive relaxation quenching in geiger mode for synthesis of arbitrary gain images, " in IEEE Int. Solid-State Circuits Conf. (ISSCC) Dig. Tech. Papers, Feb. 2019, pp. 104-106.
T. Okino, et al., "A 1200×900 6?m 450fps geiger-mode vertical avalanche photodiodes CMOS image sensor for a 250m time-offlight ranging system using direct-indirect-mixed frame synthesis with configurable-depth-resolution down to 10cm, " in IEEE Int. Solid-State Circuits Conf. (ISSCC) Dig. Tech. Papers, Feb. 2020, pp. 96-98.
D. Bronzi, F. Villa, S. Tisa, A. Tosi, F. Zappa, "SPAD figures of merit for photon-counting, photon-timing, imaging applications: A review, " IEEE Sensors J., vol. 16, no. 1, pp. 3-12, Jan. 2016.