SPAD Optical Ranging Fault Detection Using Clutter-Light Dead Time
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Solution Overview
Problem
Existing optical ranging devices face challenges in accurately detecting abnormalities in the light receiving unit due to ambient light variability, particularly in vehicle environments, which can lead to measurement degradation and failures.
Innovation Solution
The device utilizes clutter reflected light within the housing to detect abnormalities in the light receiving unit by analyzing signals from single photon avalanche diodes (SPADs) during specific time periods, such as the clutter reflected light period and dead time, to determine the presence of SPADs in Low- or High-abnormal states.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the optical ranging device uses SPADs to detect reflected light in environments with variable ambient light, then the device can operate in practical applications like vehicle use, but the ability to accurately detect abnormalities in the light receiving unit deteriorates due to ambient light interference
Solution Approach 1:
The detection process is segmented into distinct time periods: a first time period for detecting clutter reflected light to assess light receiving unit status, and a second time period for normal distance measurement. This temporal segmentation allows abnormality detection to be performed independently without interference from ambient light conditions during normal operation.
Solution Approach 2:
The device performs preliminary detection of clutter reflected light in a first time period before conducting normal distance measurements. By detecting the presence and characteristics of clutter reflected light in advance, the system establishes a baseline for light receiving unit performance that is independent of subsequent ambient light variations during measurement.
2Reliability
If the device performs continuous abnormality detection using ambient light, then abnormality detection can be performed in constant ambient light environments, but the detection becomes unreliable in environments with variable ambient light such as vehicle use
Solution Approach 1:
The device converts the previously harmful clutter reflected light (which caused detection errors in variable ambient light) into a useful detection signal. By intentionally detecting clutter reflected light in a controlled first time period, the system transforms an interference source into a diagnostic tool for assessing light receiving unit status independent of ambient light conditions.
Solution Approach 2:
Clutter reflected light serves as an intermediary signal for abnormality detection. Instead of relying directly on ambient light levels which vary with environment, the system uses the internally generated clutter reflected light as a mediator to indirectly assess light receiving unit performance, thereby decoupling detection reliability from ambient light conditions.
3Measurement precision
If the device uses clutter reflected light for abnormality detection, then accurate detection can be performed in variable ambient light environments, but the device complexity increases due to additional detection mechanisms
Solution Approach 1:
The light receiving unit serves dual purposes: it detects both clutter reflected light for abnormality assessment and measurement reflected light for distance measurement. The same SPAD array and signal processing circuitry are reused for both functions, with only temporal separation required. This self-service approach enables accurate abnormality detection without adding separate detection hardware.
Solution Approach 2:
The light receiving unit is designed with universal functionality to perform multiple tasks: detecting clutter reflected light for abnormality detection, detecting measurement reflected light for distance measurement, and operating across variable ambient light conditions. This multi-functionality is achieved through temporal multiplexing rather than hardware duplication, maintaining simplicity while enabling precise detection.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method allows for accurate detection of abnormalities in the light receiving unit, even in environments with variable ambient light, preventing hypersensitive detection and maintaining reliable distance measurements.
Implementation Method 1
a light receiving unit 30 which has a light-receiving surface provided with an array of single photon avalanche diodes (SPADs) and which uses the SPADs to detect photons of reflected light
Implementation Method 2
measures a distance to an object based on a time of flight (TOF) of light from emission of the light into a measurement region to receipt of its reflected light from the object
Data Source
AI summary
In an optical ranging device, a light source unit is configured to emit irradiation light to irradiate a measurement region, and a light receiving unit has a light-receiving surface provided with an array of single photon avalanche diodes (SPADs) and is configured to use the SPADs to detect photons of reflected light of the irradiation light. A controller is configured to control the light source unit and the light receiving unit and perform a distance measurement process to measure a distance to an object in the measurement region using signals output from the SPADs upon receipt of measurement reflected light that is reflected light of the irradiation light from the object in the measurement region. A determiner is configured to determine presence or absence of an abnormality in the light receiving unit using signals output during a dead time following incidence of photons of clutter reflected light on the SPADs.