ToF Pixel Storage Nodes for High Dynamic Range Depth Sensing
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Solution Overview
Problem
Current time-of-flight (ToF) depth sensing systems face limitations in dynamic range, where pixels imaging closer objects can saturate, leading to signal clipping, while reducing light to avoid clipping results in poor signal-to-noise ratio for farther objects, affecting depth determination.
Innovation Solution
The implementation of a ToF camera with multiple storage nodes per pixel tap, including short-exposure and long-exposure nodes, allows for charge integration during different intervals, capturing both signals in a single frame to extend full well capacity and avoid motion artifacts, thereby enhancing dynamic range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If light exposure time is increased to improve signal-to-noise ratio for farther objects, then signal quality improves, but closer objects cause pixel saturation and signal clipping
Solution Approach 1:
The pixel structure is segmented into multiple independent storage nodes (first storage node, second storage node, third storage node) that can independently integrate charge from different exposure intervals. This segmentation allows simultaneous capture of both bright (close) and dim (far) objects without mutual interference, resolving the saturation vs. signal-to-noise ratio contradiction.
Solution Approach 2:
The patent implements dynamic control of exposure intervals through configurable switch gates that direct charge to different storage nodes based on timing. The system dynamically adapts exposure duration for different spatial regions, enabling long exposure for distant objects and short exposure for nearby objects within the same frame, thus preventing saturation while maintaining signal quality.
2Adaptability or versatility
If sequential exposures are used to capture both close and far objects, then dynamic range is extended, but motion artifacts increase
Solution Approach 1:
Multiple storage nodes within each pixel are merged to simultaneously hold charge from different exposure intervals. The first storage node captures charge during a first exposure interval, the second storage node captures charge during a second exposure interval, and both are read out within the same frame period. This merging enables capture of both close and far objects in a single instantaneous frame, eliminating motion artifacts while maintaining extended dynamic range.
3Adaptability or versatility
If multiple storage nodes per pixel are implemented, then full well capacity is extended and dynamic range improves, but device complexity increases
Solution Approach 1:
Multiple storage nodes share common readout circuitry and control mechanisms, allowing the system to operate in different modes (single exposure, dual exposure, alternating exposure) without requiring separate dedicated circuits for each function. This multi-functionality approach extends full well capacity while controlling complexity through resource sharing.
Solution Approach 2:
The patent configures different exposure intervals and charge integration times for different storage nodes through controllable switch gates. By dynamically changing the integration time parameter for each storage node, the system optimizes the balance between capacity and complexity, allowing flexible adaptation to different imaging scenarios without hardware reconfiguration.
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 increases the dynamic range of ToF image sensors, preventing signal clipping for closer objects and improving signal quality for farther objects, resulting in more accurate depth determination without compromising on motion artifacts.
Implementation Method 1
each tap comprising a photogate... configured to direct charge generated during the short-exposure interval to the short-exposure storage node
Data Source
AI summary
Examples are disclosed that relate to time of flight imaging using long-exposure and short-exposure storage nodes for each pixel tap of a pixel in an image sensor. One example provides a time-of-flight camera, comprising an image sensor comprising a plurality of pixels, each pixel of the plurality of pixels comprising one or more taps, each tap comprising a photogate, a short-exposure storage node configured to receive charge during a short-exposure interval of an integration period, a long-exposure storage node configured to receive charge during a long-exposure interval of the integration period, a short-exposure switch gate configured to direct charge generated during the short-exposure interval to the short-exposure storage node, a long-exposure switch gate configured to direct charge generated during the long-exposure period to the long-exposure storage node, and a readout mechanism comprising one or more floating diffusion capacitors.