SPAD Cluster Gating for Ambient Light Saturation in ToF Ranging
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Solution Overview
Problem
Time-of-flight ranging systems face degradation in performance due to ambient light, leading to saturation and reduced signal-to-ambient light ratios, which affects target detection and range accuracy.
Innovation Solution
The system employs a method to gate the output of SPAD clusters based on ambient light counts, excluding clusters that contribute disproportionately to ambient light levels, thereby preventing saturation and enhancing the signal-to-ambient light ratio by dynamically adjusting the number of active SPADs in each cluster.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If all SPAD clusters are used to detect reflected light, then the coverage and detection capability are improved, but the signal-to-ambient light ratio deteriorates due to ambient light saturation
Solution Approach 1:
The SPAD array is divided into multiple clusters, and each cluster is independently evaluated and gated based on its ambient light count. This segmentation allows selective inclusion of clusters with good signal-to-ambient ratios while excluding those with high ambient light saturation, thereby maintaining detection capability while reducing harmful ambient light effects.
Solution Approach 2:
Different SPAD clusters are treated differently based on their local ambient light conditions.Clusters with low ambient light counts are included in the histogram calculation, while clusters with high ambient light counts are excluded. This local differentiation optimizes the signal-to-ambient ratio for each region while maintaining overall system performance.
2Measurement precision
If the number of active SPADs is increased to improve detection sensitivity, then the signal detection capability is improved, but the susceptibility to ambient light interference increases
Solution Approach 1:
The system dynamically adjusts which SPAD clusters are active by gating them based on real-time ambient light counts. The controller continuously monitors ambient light levels and adjusts the number of active SPADs accordingly, optimizing the balance between detection sensitivity and ambient light susceptibility in a dynamic manner.
Solution Approach 2:
The system uses feedback from ambient light counters to control the gating of SPAD clusters. The controller receives feedback on ambient light counts and adjusts the number of active SPADs accordingly, creating a closed-loop system that automatically optimizes detection performance based on ambient conditions.
3Area of stationary object
If SPAD clusters with high ambient light counts are included in the histogram, then the coverage is improved, but the ranging performance deteriorates due to reduced signal-to-ambient ratio
Solution Approach 1:
The SPAD array is segmented into clusters that are independently evaluated. Clusters are divided into two groups: those with ambient light counts below a threshold (included in histogram) and those above the threshold (excluded from histogram). This segmentation allows the system to maintain coverage through included clusters while preserving ranging performance by excluding degraded clusters.
Solution Approach 2:
Clusters with high ambient light counts are extracted (removed) from the histogram calculation. The controller identifies and excludes these clusters from the ranging computation, thereby removing the harmful effect of ambient light interference while maintaining the contribution of clusters with better signal-to-ambient ratios.
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 improves the ranging performance by increasing the signal-to-ambient light ratio, enabling better target detection and measurement of longer distances with improved repeatability in high ambient light scenarios.
Implementation Method 1
A photon may generate a carrier in the SPAD through the photo electric effect. The photo generated carrier may trigger an avalanche current in one or more of the SPADs in a SPAD array.
Implementation Method 2
The photo generated carrier may trigger an avalanche current in one or more of the SPADs in a SPAD array.
Implementation Method 3
This method comprises sending a light signal towards the object and measuring the time taken by the signal to travel to the object and back.
Data Source
AI summary
In an embodiments, a method for operating a time-of-flight (ToF) ranging array includes: illuminating a field-of-view (FoV) of the ToF ranging array with radiation pulses; receiving reflected radiation pulses with a plurality of single photon avalanche diodes (SPADs) in a region of interest (ROI) of the ToF ranging array, the plurality of SPADs arranged in a plurality of SPAD clusters; determining an ambient count of ambient light events generated by SPADs of a first SPAD cluster of the plurality of SPAD clusters; and gating an output of the first SPAD cluster based on the ambient count.