Solid-State Image Sensor White Pixel Dynamic Range Expansion
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Solution Overview
Problem
Conventional solid-state image sensors with white pixels suffer from limited dynamic range in the high luminance region due to saturation at lower luminance levels compared to red, green, and blue pixels, restricting the range of brightness information that can be captured.
Innovation Solution
Incorporating white or yellow pixels with additional capacitance on a semiconductor substrate, along with red, green, and blue pixels, to expand the dynamic range by allowing photocharges to accumulate and separate capacitance from the floating diffusion, thereby enhancing the sensitivity in both low and high luminance regions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If white pixels with no color filter are added to improve sensitivity in low luminance region, then sensitivity is improved, but dynamic range is limited due to saturation at lower luminance than RGB pixels
Solution Approach 1:
The pixel structure is segmented into two distinct capacitance components: a first capacitance (floating diffusion) and a second capacitance (additional capacitance element). This segmentation allows independent control of charge storage regions, enabling the first capacitance to handle low luminance signals with high sensitivity while the second capacitance accommodates high luminance signals, thereby resolving the contradiction between sensitivity and dynamic range.
Solution Approach 2:
The invention changes the capacitance parameter by introducing an additional capacitance element that can be selectively coupled to the floating diffusion. By adjusting the coupling state of the second capacitance through the capacitance coupling transistor, the system can dynamically alter the total charge storage capacity, enabling adaptation to different luminance levels and expanding the dynamic range while maintaining high sensitivity.
2Measurement precision
If white pixels are used to improve sensitivity, then quantum efficiency is improved, but the saturation level is reached at lower luminance limiting high luminance capture
Solution Approach 1:
The second capacitance element is nested within the pixel structure and can be selectively coupled to the floating diffusion through the capacitance coupling transistor. This nested configuration allows the additional capacitance to be integrated into the existing pixel architecture without disrupting the photodiode and floating diffusion structure, thereby maintaining high quantum efficiency while providing extra charge storage capacity for high luminance signals.
Solution Approach 2:
The invention introduces dynamic control through the capacitance coupling transistor that can selectively couple or decouple the second capacitance from the floating diffusion. This dynamic adjustment allows the pixel to adapt its charge storage capacity in real-time based on the incident luminance level, maintaining optimal performance across a wide range of illumination intensities from low to high luminance.
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 expands the dynamic range from 80 dB to 100 dB or more, improving sensitivity in both low and high luminance regions, allowing for a wider range of brightness information capture without sacrificing quantum efficiency.
Implementation Method 1
a photodiode that receiving light and generating and accumulating photocharges
Data Source
AI summary
This invention is a solid-state image pickup device that solves the problem of limited dynamic range in the high luminance region in an image sensor having white pixels. White pixels or yellow pixels and at least red pixels, green pixels or blue pixels are arranged in array form on the light receiving surface of a semiconductor substrate. White pixels or yellow pixels have an additional capacitance CS connected to the photodiode via the floating diffusion, a capacitance coupling transistor S that can couple or separate the floating diffusion and the additional capacitance. The proportion of white or yellow pixels to the total number of pixels is higher in a central portion of the light receiving surface than a peripheral portion. The white or yellow pixel may share a floating diffusion with a red, green or blue pixel.