SPAD Array Distance Measurement Using Time-Gated Detection
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Pulsed time-of-flight laser distance measurement devices using Single Photon Avalanche Detectors (SPADs) face unreliable results due to background illumination and thermal noise, leading to incorrect timings and distances, as existing methods to minimize these issues are either impractical or lengthen measurement time without ensuring reliability.
Innovation Solution
The implementation of a time-gated detection system using an array of SPADs in Geiger mode, where detector elements are activated only during specific time windows, reducing random triggers and enhancing the signal-to-noise ratio by filtering out background noise through adaptive time-gating and threshold-based detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If SPAD is used as a detector to increase sensitivity, then detection capability is improved, but wrong detections due to background illumination and thermal noise increase
Solution Approach 1:
The detector is activated in periodic time-gated windows synchronized with the transmitted optical pulses. By enabling the detector only during specific time intervals when reflected pulses are expected and disabling it during intervals when background illumination and thermal noise occur, the system maintains high detection sensitivity while minimizing wrong detections. This periodic activation pattern resolves the contradiction by temporally separating useful signal detection from noise accumulation.
2Reliability
If background illumination is minimized to reduce wrong detections, then detection reliability is improved, but measurement applicability in various environments deteriorates
Solution Approach 1:
The time-gated detection system enables measurements in diverse environments by periodically activating the detector only during windows when reflected optical pulses are expected. This approach maintains high detection reliability across varying background illumination conditions (indoor, outdoor, different lighting) because the detector ignores continuous background light and only responds to temporally-synchronized reflected pulses, thereby achieving both reliability and environmental adaptability.
3Reliability
If the number of measurements is increased to separate wrong detections from correct detections, then detection reliability is improved, but measurement time increases substantially
Solution Approach 1:
By implementing time-gated detection that periodically activates the detector only during windows when reflected pulses are expected, the system achieves reliable detection in a single measurement pass. The periodic gating inherently filters out wrong detections caused by thermal noise and background illumination, eliminating the need for multiple repeated measurements and subsequent algorithmic separation, thereby maintaining high reliability while minimizing measurement time.
4Measurement precision
If detector is continuously active to detect all optical signals, then detection coverage is improved, but wrong detections due to thermal noise and background illumination increase
Solution Approach 1:
The detector operates in periodic time-gated windows that are synchronized with the transmission of optical pulses. During these brief activation windows, the detector captures reflected pulses with full sensitivity and coverage. Between windows, the detector remains inactive, preventing accumulation of wrong detections from thermal noise and continuous background illumination. This periodic operation maintains comprehensive detection coverage for valid signals while eliminating harmful wrong detections.
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 approach significantly improves the reliability of distance measurements by minimizing wrong and random detections, thereby enhancing the accuracy and speed of the measurement process while tolerating high background illumination and thermal noise.
Implementation Method 1
an array of single photon avalanche detector elements of a Geiger mode, each of the array of single photon avalanche detector elements being enabled to detect a photon
Data Source
Figure 1~2A
Figure 2B~3
Figure 4~5A
AI summary
A the receiver unit (105) comprises at least one single photon avalanche detector element (250 to 266) of a Geiger mode, time-to-digital converter circuit (208) and a processing unit (210). Each single photon avalanche detector element (250 to 266) is enabled to detect a photon in at least one time-gated window, and each single photon avalanche detector element (250 to 266) is configured to output an electric pulse in response to detection of a photon of optical radiation within the at least one time-gated window. The time-to-digital converter circuit (208) provides timing data associated with said electric pulse for determination of a distance of a target (112) on the basis of the timing data provided by the time-to-digital converter circuit (206).