A novel sub-10 ps resolution TDC for CMOS SPAD array

Sesta, Vincenzo; Villa, Federica; Conca, Enrico; Tosi, Alberto

doi:10.1109/icecs.2018.8617859

Cited by 8 publications

(6 citation statements)

References 6 publications

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“…The implemented TDCs are based on an architecture employing a multiphase clock interpolation based on a Delay-Locked Loop (DLL) [28], [29], which generates 16 clock phases from a 400 MHz reference clock; each of these clock phases is delayed by 78 ps from one another. Each 16 clock phases can be tuned, to compensate any delay mismatch, thus improving the overall TDC linearity.…”

Section: Smart Tdc Sharingmentioning

confidence: 99%

Range-Finding SPAD Array With Smart Laser-Spot Tracking and TDC Sharing for Background Suppression

Sesta

Pasquinelli

Federico

et al. 2022

IEEE Open J. Solid-State Circuits Soc.

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We present the design and experimental characterization of a CMOS sensor based on Single-Photon Avalanche Diodes for direct Time-Of-Flight single-point distance ranging, under high background illumination for short-range applications. The sensing area has a rectangular shape (40 × 10 SPADs) to deal with the backscattered light spot displacement across the detector, dependent on target distance, due to the non-confocal optical setup. Since only few SPADs are illuminated by the laser spot, we implemented a smart laser-spot tracking within the active area, so to define the specific Region-Of-Interest (ROI) with only SPADs hit by signal photons and a smart sharing of the timing electronics, so to significantly improve Signal-to-Noise Ratio (SNR) of TOF measurements and to reduce overall chip area and power consumption. The timing electronics consists of 80 Time-to-Digital Converter (TDC) shared among the 400 SPADs with a self-reconfigurable routing, which dynamically connects the SPADs within the ROI to the available TDCs. The latter have 78 ps resolution and 20 ns Full-Scale Range (FSR), i.e., up to 2 m maximum distance range. An on-chip histogram builder block accumulates TDC conversions so to provide the final TOF histogram. We achieve a precision better than 2.3 mm at 1 m distance and 80% target reflectivity, with 3 klux halogen lamp background illumination and 2 kHz measurement rate. The sensor rejects 10 klux of background light, still with a precision better than 20 mm at 2 m.INDEX TERMS Light detection and ranging (LiDAR), laser rangefinder, time-of-flight (TOF), time-todigital converter (TDC), single photon avalanche diode (SPAD), background light rejection.VINCENZO SESTA was born in Ribera, Italy, in 1991. He received the master's degree in electronics engineering and the Ph.D. degree in information technology from the Politecnico di Milano, Milan, Italy, in 2016 and 2020, respectively, where he is currently a Postdoctoral Researcher with the Department of Electronics, Information and Bioengineering. His research activity focuses on the design and development of time-to-digital converters and timing electronics CMOS circuits for arrays of silicon SPADs.KLAUS PASQUINELLI was born in Seriate, Italy, in 1994. He received the bachelor's and M.Sc. degrees in electronics engineering from the Politecnico di Milano in 2016 and October 2018, respectively, where he is currently pursuing the Ph.D. degree in information technology. His research interests include the design, development, and testing of systems with single-photon avalanche diodes matrices and digital silicon photomultiplier.

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Section: Smart Tdc Sharingmentioning

confidence: 99%

Range-Finding SPAD Array With Smart Laser-Spot Tracking and TDC Sharing for Background Suppression

Sesta

Pasquinelli

Federico

et al. 2022

IEEE Open J. Solid-State Circuits Soc.

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“…Since the single-shot precision is dominated by the 3 ns laser FWHM (variance σ = 1.27 ns), the Least-Significant Bit (LSB) of the TDC must be set shorter in order to make its σ TDC uncertainty contribution negligible with respect to the laser variance σ laser (see Equation (2). An LSB of about 100 ps or slightly shorter can be easily implemented in cost-effective CMOS technology [12,31], so to possibly allow for the exploitation of even better (shorter pulse) and more expensive lasers.…”

Section: Tdc Performancementioning

confidence: 99%

“…The FSR of the TDC is set by the maximum distance range to be detected, which is at least 1 m in our application (i.e., a TOF of 6.7 ns); thus, 10 ns FSR is a reasonable value, with a corresponding low number of bits (6–7 bits, given the 10 ns FSR and about 100 ps LSB), so a coarse TDC suffice, with no need to implement a finer TDC architecture [ 12 , 31 ].…”

Section: Required Detector Performancementioning

confidence: 99%

Spot Tracking and TDC Sharing in SPAD Arrays for TOF LiDAR

Sesta

Severini

Villa

et al. 2021

Sensors

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Light Detection and Ranging (LiDAR) is a widespread technique for 3D ranging and has widespread use in most automated systems that must interact with the external environment, for instance in industrial and security applications. In this work, we study a novel architecture for Single Photon Avalanche Diode (SPAD) arrays suitable for handheld single point rangefinders, which is aimed at the identification of the objects’ position in the presence of strong ambient background illumination. The system will be developed for an industrial environment, and the array targets a distance range of about 1 m and a precision of few centimeters. Since the laser spot illuminates only a small portion of the array, while all pixels are exposed to background illumination, we propose and validate through Monte Carlo simulations a novel architecture for the identification of the pixels illuminated by the laser spot to perform an adaptive laser spot tracking and a smart sharing of the timing electronics, thus significantly improving the accuracy of the distance measurement. Such a novel architecture represents a robust and effective approach to develop SPAD arrays for industrial applications with extremely high background illumination.

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“…Photoelectrons generated by the absorption of individual photons are accelerated by the strong electric field in the diode and undergo an avalanche multiplication process that produces a macroscopic, measurable current through the device [10]. Events detected by the SPAD pixels are often timed on-chip using combinations of time-to-analog converters (TACs) and analog-to-digital converters (ADCs) [11,12], or time-to-digital converters (TDCs) [13][14][15], to produce a digital representation of the time of arrival of each detected photon, called a timestamp. Each timestamp T ts is a measure of the time of arrival of a photon detected by the pixel T pixel relative to the generation time of the laser pulse T 0 , according to the relation…”

Section: Tcspc Lidarmentioning

confidence: 99%

An Optical Interference Suppression Scheme for TCSPC Flash LiDAR Imagers

Carrara¹,

Fiergolski²

2019

Applied Sciences

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This paper describes an optical interference suppression scheme that allows flash light detection and ranging (LiDAR) imagers to run safely and reliably in uncontrolled environments where multiple LiDARs are expected to operate concurrently. The issue of optical interference is a potential show-stopper for the adoption of flash LiDAR as a technology of choice in multi-user application fields such as automotive sensing and autonomous vehicle navigation. The relatively large emission angle and field of view of flash LiDAR imagers make them especially vulnerable to optical interference. This work illustrates how a time-correlated single-photon counting LiDAR can control the timing of its laser emission to reduce its statistical correlation to other modulated or pulsed light sources. This method is based on a variable random delay applied to the laser pulse generated by LiDAR and to the internal circuitry measuring the time-of-flight. The statistical properties of the pseudorandom sequence of delays determines the effectiveness of LiDAR resilience against unintentional and intentional optical interference. For basic multi-camera operation, a linear feedback shift register (LFSR) was used as a random delay generator, and the performance of the interference suppression was evaluated as a function of sequence length and integration time. Direct interference from an identical LiDAR emitter pointed at the same object was reduced up to 50 dB. Changing integration time between 10 ms and 100 ms showed a marginal impact on the performance of the suppression (less than 3 dB deviation). LiDAR signal integrity was characterized during suppression, obtaining a maximum relative deviation of the measured time-of-flight of 0.1%, and a maximum deviation of measurements spread (full-width half-maximum) of 3%. The LiDAR signal presented an expected worst-case reduction in intensity of 25%.

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A novel sub-10 ps resolution TDC for CMOS SPAD array

Cited by 8 publications

References 6 publications

Range-Finding SPAD Array With Smart Laser-Spot Tracking and TDC Sharing for Background Suppression

Range-Finding SPAD Array With Smart Laser-Spot Tracking and TDC Sharing for Background Suppression

Spot Tracking and TDC Sharing in SPAD Arrays for TOF LiDAR

An Optical Interference Suppression Scheme for TCSPC Flash LiDAR Imagers

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