Multi-Tap Pixel Architecture for HDR Image Sensors
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Solution Overview
Problem
Current HDR image sensors face challenges in reducing motion artifacts and compromising resolution due to the need for multiple exposures, which are difficult to control precisely, especially for small pixel sensors, and result in limited dynamic range extension.
Innovation Solution
The image sensor employs a multi-tap pixel architecture with a photodetector and multiple storage nodes, where photocharge packets are accumulated during different exposure periods and transferred to storage nodes, allowing for the generation of high dynamic range image frame data by integrating sub-exposure times, thereby reducing motion artifacts and enhancing dynamic range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If multiple exposures are taken at different exposure times to increase dynamic range, then dynamic range is improved, but motion artifacts are introduced
Solution Approach 1:
The pixel is divided into multiple storage nodes (first storage node, second storage node) that can independently store charges from different exposure periods. This segmentation allows simultaneous capture of multiple exposure times within a single frame, eliminating motion artifacts while maintaining dynamic range extension capability.
Solution Approach 2:
The patent employs periodic exposure sampling where the photodetector alternates between different exposure periods (first exposure time, second exposure time) during a single frame period. This periodic action captures multiple luminance ranges systematically, enabling HDR reconstruction without temporal misalignment issues.
2Illumination intensity
If consecutive frames are sampled at different exposures to obtain multiple samples, then dynamic range is extended, but resolution is compromised
Solution Approach 1:
The patent merges multiple exposure samples from the same pixel within a single frame period by using multiple storage nodes. This combining approach maintains spatial resolution while achieving dynamic range extension, as all samples originate from the same spatial location without requiring frame concatenation.
3Reliability
If dual gain conversion is used to obtain bright and dark condition samples, then motion artifacts are reduced, but dynamic range extension is limited by gain ratio control difficulty
Solution Approach 1:
Instead of adjusting conversion gain, the patent changes the exposure time parameter to capture different luminance ranges. By varying exposure duration (first exposure time vs. second exposure time) while maintaining fixed conversion gain, the system achieves HDR without the complexity of precise gain control, particularly benefiting small pixel sensors.
4Illumination intensity
If multiple storage nodes are used to capture different exposure times, then dynamic range is enhanced, but pixel circuit complexity increases
Solution Approach 1:
The photodetector serves multiple functions by sequentially transferring charges to different storage nodes during different exposure periods within the same frame. This multi-functionality allows a single photodetector to capture multiple luminance ranges, reducing the need for additional photodetectors while extending dynamic range.
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 effectively reduces motion artifacts and enhances dynamic range by generating HDR image frame data with improved resolution and flexibility, as the integrated exposure times represent incident light over a consistent timeframe, allowing for more accurate luminance sampling.
Implementation Method 1
activating a photodetector responsive to incoming light for a plurality K of exposure periods and thereby accumulate K respective photocharge packets
Data Source
AI summary
An image sensor may include control circuitry, a plurality of pixels, and an image processor. Each pixel includes a photodetector, at least first and second storage nodes, and transfer circuitry. The transfer circuitry is responsive to control signals generated by the control circuitry to transfer first charges generated by the photodetector during a first exposure time within a frame period to the first storage node. Second charges may be generated by the photodetector during a second, longer exposure time during the frame period, and transferred to the second storage node. The image processor may generate image frame data based on output voltage samples derived from the first and second charges of each of the plurality of pixels.