A CMOS Integrator-Based Clock-Free Time-to-Digital Converter for Home-Monitoring LiDAR Sensors.

Ying He,Sung Min Park

doi:10.3390/s22020554

Abstract

This paper presents a nine-bit integrator-based time-to-digital converter (I-TDC) realized in a 180 nm CMOS technology for the applications of indoor home-monitoring light detection and ranging (LiDAR) sensors. The proposed I-TDC exploits a clock-free configuration so as to discard clock-related dynamic power consumption and some notorious issues such as skew, glitch, and synchronization. It consists of a one-dimensional (1D) flash TDC to generate coarse-control codes and an integrator with a peak detection and hold (PDH) circuit to produce fine-control codes. A thermometer-to-binary converter is added to the 1D flash TDC, yielding four-bit coarse codes so that the measured detection range can be represented by nine-bit digital codes in total. Test chips of the proposed I-TDC demonstrate the measured results of the 53 dB dynamic range, i.e., the maximum detection range of 33.6 m and the minimum range of 7.5 cm. The chip core occupies the area of 0.14 × 1.4 mm2, with the power dissipation of 1.6 mW from a single 1.2-V supply.

Highlights

Light detection and ranging (LiDAR) sensors have been exploited in various time-of-flight (ToF) applications, including unmanned autonomous vehicles that can drive safely by recognizing the surrounding environment with real-time three-dimensional (3D)mapping, e.g., Google self-driving cars with panoramic scan sensors [1]; home-monitoringlight detection and ranging (LiDAR) sensors for either single elders living alone or senile dementia patients residing in nursing homes [2,3]; and remote sensing LiDAR sensors for the purpose of observation of forestry, the cryosphere, aerosols, and clouds.In particular, home-monitoring LiDAR sensors have become urgently needed to help professional nurses take care of their dementia patients more efficiently
The results (F1–F15) of the integrator-based to-digital converter (TDC) (I-TDC) are compared with VH, resulting in a coarse thermometer code that will be eventually converted to a binary code
It is noted here that only a five-bit ADC with 15 switches connecting F1–F15 can be utilized for this proposed I-TDC, enabling us to avoid the undesired increase of power consumption

Summary

Introduction

Home-monitoring LiDAR sensors have become urgently needed to help professional nurses take care of their dementia patients more efficiently. It is almost impossible to detect these falling accidents in real-time, especially when we consider the situations of senile dementia patients living alone at home and those staying in nursing homes where only one or two professional nurses reside and take care of 10–20 patients simultaneously. Even for those living with their families, it could be barely feasible. It would be an efficient solution to equip home-monitoring LiDAR sensors in houses and at nursing homes to ensure that these accidents can be detected instantly and alarms can be conveyed to either nurses or families in real-time, enabling prevention of more seriously dangerous incidents

Results

Discussion

Conclusion