Depth Sensor Pixel Segmentation for Background Light Saturation
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Solution Overview
Problem
Active depth sensing methods face challenges with pixel saturation due to strong background light, leading to distortion and inaccurate depth value calculations, particularly in environments with high ambient illumination.
Innovation Solution
A depth sensing apparatus that calculates a difference voltage between two floating diffusion nodes using sub-integration periods and feeds back this voltage to prevent saturation, allowing for accurate depth value calculation by eliminating common-mode charge and storing the difference value in the nodes, thereby enhancing pixel capacity without degrading space resolution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the size of storage capacitor is increased to increase pixel capacity, then the pixel's capacity is improved, but the space resolution and fill factor of the pixel are degraded
Solution Approach 1:
The integration period is divided into multiple sub-integration periods, and the pixel capacity is segmented into multiple storage capacitors (first storage capacitor and second storage capacitor). This allows the system to accumulate charge from multiple phases without requiring a single large capacitor, thus maintaining high pixel capacity while preserving space resolution.
Solution Approach 2:
Multiple storage capacitors are nested within the pixel structure, with each capacitor handling charge from different phase intervals. This nested arrangement allows efficient use of pixel area while providing sufficient total capacity to handle background light without degrading space resolution.
2Measurement precision
If the integration period is extended to improve depth sensing accuracy, then the measurement precision is improved, but the pixel saturation due to background light is worsened
Solution Approach 1:
The integration period is divided into multiple sub-integration periods (first phase interval, second phase interval, etc.). Each phase accumulates charge in separate storage capacitors, allowing the system to extend the total integration time while preventing any single capacitor from saturating due to background light accumulation.
Solution Approach 2:
Charge accumulated in storage capacitors from different phase intervals is sequentially transferred to floating diffusion nodes. This process allows the system to recover and utilize charge from multiple phases while discarding saturated charge from individual phases, thereby extending effective integration time without saturation.
3Reliability
If the pixel capacity is increased to handle strong background light, then the reliability is improved, but the space resolution and fill factor are degraded
Solution Approach 1:
The pixel capacity is segmented into multiple storage capacitors instead of using a single large capacitor. This segmentation allows the system to handle strong background light through multiple smaller capacitors working in parallel, thereby maintaining high fill factor while improving reliability in bright environments.
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
The solution effectively eliminates distortion caused by background light and prevents pixel saturation, resulting in improved accuracy and reliability of depth value calculations, even in high-illumination environments.
Implementation Method 1
a voltage of a photodiode stored in the first floating diffusion node in a first phase interval and a voltage of the photodiode stored in the second floating diffusion node in a second phase interval
Data Source
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Figure 2A
Figure 2B
AI summary
A depth sensing apparatus and method for acquiring a depth image of a target object may calculate a difference voltage between a first floating diffusion node and a second floating diffusion node, based on a voltage of a photodiode stored in the first floating diffusion node in a first phase interval and a voltage of the photodiode stored in the second floating diffusion node in a second phase interval, using a sub-integration period, may feed back the difference voltage to one of the first floating diffusion node and the second floating diffusion node, and may calculate a depth value of a pixel based on difference voltages accumulated during an integration period including sub-integration periods.