Asymmetric Charge Storage Wells for Range-Gating Pixel Saturation
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Solution Overview
Problem
Existing range-gating based imaging systems face saturation issues with short-range reflections, limiting their accuracy and operational range, especially in automotive applications where high accuracy at short ranges is required without compromising performance in bright ambient light conditions.
Innovation Solution
A pixel architecture with a first charge storage well having at least 50% greater capacity than a second well, and a third well with smaller capacity, allowing for asymmetric charge distribution and background light subtraction, enabling reduced saturation and improved dynamic range without additional pixel surface area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If pixels are used in range-gating based imaging systems, then distance determination capability is achieved, but pixels get saturated by reflections from objects at short distances
Solution Approach 1:
The pixel is divided into multiple charge storage wells (first well, second well, third well) with different capacities. The first well with larger capacity handles short-range reflections, while the second and third wells with smaller capacities handle long-range measurements, segmenting the dynamic range handling across multiple storage regions.
Solution Approach 2:
Different charge storage wells are assigned different capacities based on their specific function. The first well has at least 50% greater capacity than the second well to specifically handle strong short-range reflections, while the third well has smaller capacity for background light subtraction, creating local quality differentiation within the pixel structure.
2Object-affected harmful factors
If additional charge storage wells are added to increase dynamic range, then saturation resistance is improved, but pixel surface area increases
Solution Approach 1:
Multiple charge storage wells are integrated within a single pixel footprint, nesting multiple functional storage regions (first well, second well, third well) within the same pixel structure. This allows the pixel to handle multiple dynamic ranges and perform background light subtraction without increasing the overall pixel array density or surface area.
3Measurement precision
If multiple measurements are performed to handle dynamic range, then measurement accuracy is improved, but temporal resolution decreases
Solution Approach 1:
The pixel performs background light subtraction by comparing charge accumulation during periodic time windows - a first time window when the laser is off (capturing background light) and a second time window when the laser is on (capturing signal plus background). This periodic action enables real-time background rejection without requiring separate measurement passes, maintaining high temporal resolution.
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 solution reduces the need for multiple measurements, enhances temporal resolution, and prevents blooming, maintaining high spatial accuracy and allowing for accurate distance determination even with saturated pixels, while supporting long-range operations with low-power semiconductor lasers.
Implementation Method 1
a first charge storage well and a second charge storage well for accumulating electrical charges representative of amounts of light reflected by said object and impinging on said pixel
Data Source
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AI summary
The present invention pertains to a pixel for use in a system for determining a distance to an object by range gating, said pixel comprising: a first charge storage well (221) and a second charge storage well (222) for accumulating electrical charges representative of amounts of light impinging on said pixel during respective sets of exposure intervals, wherein said first charge storage well (221) has a charge capacity that is at least 50% greater than a charge capacity of said second charge storage well (222). The invention also pertains to a range gating system comprising such a pixel.