Hybrid Pixel Dynamic Range via Segmented Photodiodes
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Solution Overview
Problem
Conventional image sensors with a single predetermined dynamic range struggle to perform effectively in varying imaging conditions, such as when incident light exceeds the maximum measurable intensity or falls below the noise floor, leading to poor performance.
Innovation Solution
The implementation of hybrid pixels with multiple photodiodes and configurable operations (3T and 4T configurations) that adjust capacitance and conversion gain based on imaging conditions, allowing for improved dynamic range by selectively using the output from either photodiode depending on light intensity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a single predetermined dynamic range is used for the pixel, then the device complexity is reduced, but the adaptability to varying imaging conditions deteriorates
Solution Approach 1:
The pixel is divided into two separate photodiodes (first photodiode and second photodiode) with different capacitance values. This segmentation allows each photodiode to handle specific dynamic ranges independently, enabling the pixel to adapt to varying imaging conditions without requiring a completely complex reconfigurable architecture.
Solution Approach 2:
The pixel incorporates dynamic switching capability that allows the system to selectively activate either the first photodiode or the second photodiode based on the imaging conditions. This dynamic selection mechanism provides adaptability while maintaining relatively simple hardware structure compared to fully reconfigurable systems.
2Measurement precision
If the pixel uses a fixed capacitance value, then the manufacturing precision is improved, but the measurement precision across varying light intensities deteriorates
Solution Approach 1:
The pixel divides the measurement function into two separate photodiodes with different fixed capacitance values. Each photodiode is optimized for specific light intensity ranges, allowing high measurement precision across the full dynamic range by selecting the appropriate photodiode for the given imaging conditions.
3Adaptability or versatility
If a single photodiode is used per pixel, then the device complexity is reduced, but the dynamic range capability deteriorates
Solution Approach 1:
The pixel structure is segmented into two photodiodes with different capacitance values, allowing the system to cover a wider dynamic range by selecting the appropriate photodiode for different lighting conditions. This segmentation approach achieves extended dynamic range coverage while keeping the overall structure relatively simple.
Solution Approach 2:
The pixel achieves multi-functionality by incorporating two photodiodes that can be selectively activated based on imaging conditions. This allows a single pixel to serve multiple dynamic range requirements, enhancing adaptability without requiring multiple separate pixels or complex reconfiguration mechanisms.
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 enhances the dynamic range of image sensors, enabling better performance across a wider range of imaging conditions by accurately representing incident light levels even under conditions of saturation or low light, thereby improving image quality.
Implementation Method 1
Each pixel receives incident photons (light) and converts the photons into electrical signals
Data Source
AI summary
An imager may include hybrid pixels that can be operated in first and second configurations. A hybrid pixel may include a floating diffusion region and first and second photodiodes that are coupled to the floating diffusion region. The second photodiode may be coupled to the floating diffusion region by a transfer gate. The first photodiode may accumulate charge during a first integration period, whereas the second photodiode may accumulate charge during a second integration period. The imager may operate the hybrid pixel for improved dynamic range by controlling the configuration of the hybrid pixel.