SPAD Detector Modulated Sensitivity for Distance Estimation
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Solution Overview
Problem
SPAD detectors face challenges in accurately estimating distances due to photon saturation, especially when objects are close or have high reflectivity, leading to incorrect or unavailable distance estimates, and existing solutions compromise sensitivity, affecting signal-to-noise ratio.
Innovation Solution
The SPAD detector modulates sensitivity over time using non-uniform histograms and varying recharge times, allowing for different sensitivities in different sections of the pixel array to effectively detect photons from objects at varying distances without saturating.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the sensitivity of the SPAD detector is reduced to compensate for saturation, then saturation issues are alleviated, but the signal-to-noise ratio deteriorates
Solution Approach 1:
The patent implements dynamic sensitivity adjustment by varying the recharge time of SPAD pixels based on their distance from the cover layer. Closer pixels have longer recharge times (lower sensitivity) while farther pixels have shorter recharge times (higher sensitivity). This dynamic adaptation allows each pixel to operate in its optimal sensitivity range, preventing saturation while maintaining signal-to-noise ratio.
Solution Approach 2:
The patent applies different recharge time configurations to different spatial locations within the pixel array. Pixels at different depths from the cover layer are assigned distinct recharge time values, creating a spatially varying sensitivity profile. This local optimization ensures that each region operates at appropriate sensitivity levels for its specific detection conditions.
2Measurement precision
If the sensitivity of the SPAD detector is increased to improve detection capability, then detection sensitivity is improved, but saturation occurs for close or reflective objects
Solution Approach 1:
The system dynamically adjusts the effective sensitivity of each pixel by controlling its recharge time. Pixels that would otherwise saturate (those closer to the cover layer) are assigned longer recharge times, effectively reducing their sensitivity during periods when they would be overwhelmed by reflected photons. This dynamic control enables high detection capability without saturation.
Solution Approach 2:
Different sensitivity characteristics are assigned to different spatial locations within the detector array. Pixels closer to the cover layer, which receive stronger reflected signals, are configured with longer recharge times and thus lower effective sensitivity. Pixels farther from the cover layer have shorter recharge times and higher sensitivity, optimizing detection across the entire array.
3Device complexity
If a uniform recharge time is used for all pixels, then device complexity is reduced, but measurement precision deteriorates due to saturation or poor signal detection
Solution Approach 1:
The pixel array is segmented into multiple groups based on their distance from the cover layer, with each group assigned a specific recharge time value. This segmentation approach balances complexity and performance by creating discrete sensitivity zones rather than continuous variation, simplifying control while maintaining measurement precision across different detection ranges.
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 enables accurate distance estimation by optimizing sensitivity settings based on object distance and reflectivity, reducing saturation issues and maintaining signal quality.
Implementation Method 1
Each SPAD includes a photosensitive region that is configured to detect low levels of light (down to a single photon) and generate a corresponding output signal
Implementation Method 2
When one or more photons impinge on a SPAD, the photons may trigger an avalanche event. A triggered SPAD (i.e., a SPAD in which an avalanche event has been triggered) will produce an output pulse signal
Data Source
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AI summary
The sensitivity of one or more single-photon avalanche diodes (SPAD) in a SPAD detector is modulated over time. The sensitivity of all of the SPADs may be modulated, or the sensitivity of one section of the SPADs can be modulated differently from another section of the SPADs. Various techniques for modulating the sensitivity are disclosed.