Spot Tracking and TDC Sharing in SPAD Arrays for TOF LiDAR

Sesta, Vincenzo; Severini, Fabio; Villa, Federica; Lussana, Rudi; Zappa, Franco; Nakamuro, K.; Matsui, Yoshihiko

doi:10.3390/s21092936

Cited by 10 publications

(13 citation statements)

References 32 publications

(89 reference statements)

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“…Starting from a previous theoretical study [21], in this work we illustrate the design and characterization of a 40 × 10 single-point direct TOF sensor, showing a precision better than 2.3 mm at 1 m for an 80% reflectivity target with 3 klux background. The architecture allows to identify those SPADs actually illuminated by the signal photons due to the laser spot from those SPADs triggered by uncorrelated background photons, by means of a smart Region-Of-Interest (ROI) detection and to optimize the timing electronics by a smart sharing of the TDC electronics [24], [25].…”

Section: Introductionmentioning

confidence: 93%

“…The proposed architecture overcomes the main drawbacks of the time coincidencebased approaches because each detected signal photon is individually time-stamped, thus maximizing data collection and measurement precision. In fact, as we theoretically estimated in [21], 500 TOF acquisitions are enough to achieve an accuracy better than 10 mm with 3 klux background, using a 670 nm pulsed laser with 100 mW peak power, 1 MHz repetition rate, and width shorter than 3 ns Full Width at Half Maximum (FWHM).…”

Section: Introductionmentioning

confidence: 97%

“…The proposed ROI-based approach has some limitations due to the dependence on signal and background levels, as reported in [21], and when targets move with a transverse velocity higher than 4 m/s, since some frames could be partially lost because the ROI selection is based on the previous 500 laser pulses. Furthermore, such ROI-based approach suits single-spot measurements and not imaging, unlike time-based coincidence solutions.…”

Section: Introductionmentioning

confidence: 99%

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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: Introductionmentioning

confidence: 93%

Section: Introductionmentioning

confidence: 97%

Section: Introductionmentioning

confidence: 99%

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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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“…Moreover, since the SPAD (through its quenching and reset circuitry) provides a digital pulse if triggered by at least one photon or any other generation process (e.g., DCR), it is not possible to discriminate between one or more concurrent photons. Eventually, the triggering probability per SPAD must be kept low enough to avoid "detector's pile-up" [8], above all in high background environments, so small optical apertures and higher number of SPADs per pixel (i.e., per target spot) [9] are preferred.…”

Section: Introductionmentioning

confidence: 99%

Single-Shot Pulsed-LiDAR SPAD Sensor with on-chip Peak Detection for Background Rejection

Incoronato

Cusini

Pasquinelli

et al. 2022

IEEE J. Select. Topics Quantum Electron.

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In recent years, direct Time-of-Flight techniques have been exploited with single-photon detectors to provide long distance ranges and high-frame rates measurements. Detectors based on Silicon Photon Multipliers commonly collect repetitive laser shots to reconstruct a histogram of the TOF of returning pulsed-laser photons, so to discriminate between signal, background light, and detector noise. Instead of performing multishot measurements, we propose a single-shot technique capable to provide just one useful TOF per laser pulse, corresponding to the returning peak signal with the highest number of concurrent photons. In this way, ambient background photons and dark counts are rejected, being mostly randomly distributed over time compared to the laser pulse photons. Therefore, there is no need for repetitive laser shots, neither to acquire and store multiple TOFs, nor to post-process any TOF histogram, since each laser shot can provide the useful distance information. We present a sensor chip based on a pixel with 272 SPADs, which concurrently provide an analog signal to a peak detector triggering a multi-hit TDC each time the number of concurrent photons exceeds the previous peak. We report preliminary tests up to 25 m, rejecting 60 klux solar background, with > 95% single-shot success ratio.

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“…In Ref. [ 13 ] an array of SPADs with multi-TDCs is proposed, to provide strong background rejection and localization of the laser spot across the array. Instead, in Ref.…”

Section: Introductionmentioning

confidence: 99%

Statistical Modelling of SPADs for Time-of-Flight LiDAR

Incoronato

Locatelli

Zappa

2021

Sensors

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Time-of-Flight (TOF) based Light Detection and Ranging (LiDAR) is a widespread technique for distance measurements in both single-spot depth ranging and 3D mapping. Single Photon Avalanche Diode (SPAD) detectors provide single-photon sensitivity and allow in-pixel integration of a Time-to-Digital Converter (TDC) to measure the TOF of single-photons. From the repetitive acquisition of photons returning from multiple laser shots, it is possible to accumulate a TOF histogram, so as to identify the laser pulse return from unwelcome ambient light and compute the desired distance information. In order to properly predict the TOF histogram distribution and design each component of the LiDAR system, from SPAD to TDC and histogram processing, we present a detailed statistical modelling of the acquisition chain and we show the perfect matching with Monte Carlo simulations in very different operating conditions and very high background levels. We take into consideration SPAD non-idealities such as hold-off time, afterpulsing, and crosstalk, and we show the heavy pile-up distortion in case of high background. Moreover, we also model non-idealities of timing electronics chain, namely, TDC dead-time, limited number of storage cells for TOF data, and TDC sharing. Eventually, we show how the exploit the modelling to reversely extract the original LiDAR return signal from the distorted measured TOF data in different operating conditions.

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Spot Tracking and TDC Sharing in SPAD Arrays for TOF LiDAR

Cited by 10 publications

References 32 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

Single-Shot Pulsed-LiDAR SPAD Sensor with on-chip Peak Detection for Background Rejection

Statistical Modelling of SPADs for Time-of-Flight LiDAR

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