Abstract

This article introduces a modular, direct time-of-flight (TOF) depth sensor. Each module is digitally synthesized and features a 2 $\times $ (8 $\times $ 8) single-photon avalanche diode (SPAD) pixel array, an edge-sensitive decision tree, a shared time-to-digital converter (TDC), 21-bit per-pixel memory, and in-locus data processing. Each module operates autonomously, by internal data acquisition, management, and storage, being periodically read out by an external access. The prototype was fabricated in a TSMC 3-D-stacked 45/65-nm CMOS technology, featuring backside illumination (BSI) SPAD detectors on the top tier, and readout circuit on the bottom tier. The sensor was characterized by single-point measurements, in two different modes of resolution and range. In low-resolution mode, a maximum of 300-m and 80-cm accuracy was recorded; on the other hand, in high-resolution mode, the maximum range and accuracy were 150 m and 7 cm, respectively. The module was also used in a flexible scanning light detection and ranging (LiDAR) system, where a 256 $\times $ 256 depth map, with millimeter precision, was obtained. A laser signature based on pulse-position modulation (PPM) is also proposed, achieving a maximum of 28-dB interference reduction.

Highlights

  • C ONSTANT increase in data processing efficiency has enabled, among many other things, the intensive use of depth mapping technologies

  • The Direct TOF (dTOF) signal and ID are fed to the digital processing and communication unit (DPCU)

  • We have introduced a modular direct TOF sensor, based on todigital converter (TDC) sharing, through a edge-sensitive decision tree, and in-locus data processing and storage

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Summary

INTRODUCTION

C ONSTANT increase in data processing efficiency has enabled, among many other things, the intensive use of depth mapping technologies. Some architectures have been proposed [18] attempting to solve this problem, but the required memory renders them only feasible for an silicon photomultiplier (SiPM), singlepixel approach Another known issue with light detection and ranging (LiDAR) is regarding the interference of multiple systems on each other. We present a modular, digitally synthesized architecture for dTOF depth sensing [20] It features local time-to-digital converters (TDCs), shared among several pixels, and an in locus processing unit, capable of uncertainty reduction. It introduces a laser signature, based on pulseposition modulation (PPM), that reduces interference and increases system robustness.

DIRECT TIME-OF-FLIGHT
PROPOSED ARCHITECTURE
Decision Tree
Time-to-Digital Converter
Digital Processing and Communication Unit
Findings
CONCLUSION

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