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Open AccessFeature PaperArticle

Modeling and Analysis of a Direct Time-of-Flight Sensor Architecture for LiDAR Applications

1
AQUA Laboratory, École Polytechnique Fédérale de Lausanne (EPFL), 2000 Neuchâtel, Switzerland
2
AQUA Laboratory, Delft University of Technology (TU Delft), 2628 CD Delft, The Netherlands
*
Author to whom correspondence should be addressed.
This paper is an extended version of our paper published in: Padmanabhan, P.; Zhang, C.; Charbon, E. Analysis of a modular SPAD-based direct time-of-flight depth sensor architecture for wide dynamic range scenes in a LiDAR system. In Proceedings of the International Image Sensor Workshop, Snowbird, Utah, USA, 23 June–27 June 2019.
Sensors 2019, 19(24), 5464; https://doi.org/10.3390/s19245464
Received: 31 October 2019 / Revised: 29 November 2019 / Accepted: 5 December 2019 / Published: 11 December 2019
Direct time-of-flight (DTOF) is a prominent depth sensing method in light detection and ranging (LiDAR) applications. Single-photon avalanche diode (SPAD) arrays integrated in DTOF sensors have demonstrated excellent ranging and 3D imaging capabilities, making them promising candidates for LiDARs. However, high background noise due to solar exposure limits their performance and degrades the signal-to-background noise ratio (SBR). Noise-filtering techniques based on coincidence detection and time-gating have been implemented to mitigate this challenge but 3D imaging of a wide dynamic range scene is an ongoing issue. In this paper, we propose a coincidence-based DTOF sensor architecture to address the aforementioned challenges. The architecture is analyzed using a probabilistic model and simulation. A flash LiDAR setup is simulated with typical operating conditions of a wide angle field-of-view (FOV = 40 ° ) in a 50 klux ambient light assumption. Single-point ranging simulations are obtained for distances up to 150 m using the DTOF model. An activity-dependent coincidence is proposed as a way to improve imaging of wide dynamic range targets. An example scene with targets ranging between 8–60% reflectivity is used to simulate the proposed method. The model predicts that a single threshold cannot yield an accurate reconstruction and a higher (lower) reflective target requires a higher (lower) coincidence threshold. Further, a pixel-clustering scheme is introduced, capable of providing multiple simultaneous timing information as a means to enhance throughput and reduce timing uncertainty. Example scenes are reconstructed to distinguish up to 4 distinct target peaks simulated with a resolution of 500 ps. Alternatively, a time-gating mode is simulated where in the DTOF sensor performs target-selective ranging. Simulation results show reconstruction of a 10% reflective target at 20 m in the presence of a retro-reflective equivalent with a 60% reflectivity at 5 m within the same FOV. View Full-Text
Keywords: direct time-of-flight (DTOF) sensor; flash LiDAR; background noise; wide dynamic range targets; coincidence detection; time-gating direct time-of-flight (DTOF) sensor; flash LiDAR; background noise; wide dynamic range targets; coincidence detection; time-gating
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Padmanabhan, P.; Zhang, C.; Charbon, E. Modeling and Analysis of a Direct Time-of-Flight Sensor Architecture for LiDAR Applications. Sensors 2019, 19, 5464.

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