2x2 Pixel Sharing APS Image Sensor Color Binning
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Solution Overview
Problem
CMOS image sensors face challenges in achieving high resolution and low noise while maintaining color information in low light conditions due to the limitations of 2×2 pixel sharing schemes, which result in reduced pixel sensitivity and loss of chromatic information when binning charges from different colored pixels.
Innovation Solution
A novel color filter configuration and 2×2 pixel-sharing arrangement that allows for charge sharing between two green, two red, or two blue pixels, enabling pixel-level binning without losing color information, along with algorithms for demosaicing that include appropriate timing schemes for charge binning.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If 2×2 pixel sharing scheme is used to increase pixel density, then manufacturing cost decreases and integration increases, but pixel sensitivity decreases and light-sensitive area is insufficient
Solution Approach 1:
The patent combines multiple photodiodes (specifically two green, two red, or two blue photodiodes) into a single pixel unit, merging their light-sensitive areas to increase total pixel sensitivity while maintaining the 2×2 sharing scheme for cost-effective manufacturing. This merging allows the pixel to collect more photons without increasing individual photodiode size.
Solution Approach 2:
The patent introduces a vertical stacking dimension by placing multiple photodiodes at different depths or layers within the same pixel footprint, rather than only horizontal expansion. This allows increased light-sensitive area without proportionally increasing pixel pitch, maintaining manufacturing efficiency while improving sensitivity.
2Reliability
If charge binning is performed on pixels with different colors, then signal-to-noise ratio increases, but chromatic information is lost
Solution Approach 1:
The patent applies different binning strategies to different color channels based on their local characteristics. Green pixels, which have higher signal levels, can be binned more aggressively, while red and blue pixels use selective binning only when necessary, preserving chromatic information where it matters most.
Solution Approach 2:
The patent implements dynamic binning control where the binning operation is selectively applied based on lighting conditions and color channel requirements. The system can switch between binned and non-binned modes for different color pixels, maintaining chromatic information when needed while improving SNR when beneficial.
3Ease of manufacture
If pixel size is reduced through shrinking lithography, then manufacturing cost decreases and integration increases, but light-sensitive area becomes insufficient
Solution Approach 1:
The patent nests multiple photodiodes within a single pixel structure, placing smaller photodiode elements inside the boundaries of one logical pixel. This allows the total light-sensitive area to exceed the nominal pixel pitch area, compensating for size reduction from shrinking lithography while maintaining compact integration.
Solution Approach 2:
The patent creates a composite pixel structure combining multiple photodiode materials and color filters in a single integrated unit. This composite approach allows optimized light absorption across different wavelengths within the reduced pixel footprint, maintaining sensitivity despite smaller individual photodiode areas.
4Device complexity
If 2×2 pixel sharing is implemented, then device complexity is reduced and manufacturing is simplified, but pixel-level binning reliability decreases
Solution Approach 1:
The patent segments the pixel array into distinct 2×2 sharing groups, where each group independently performs binning operations. This segmentation isolates potential errors to individual groups, improving overall binning reliability while maintaining simplified device architecture through standardized group structures.
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
Facilitates reliable pixel-level binning for green, blue, and red pixels, maintaining color information and increasing the signal-to-noise ratio (SNR) while reducing noise, thereby enhancing image quality in low light conditions.
Implementation Method 1
Both solid-state imaging sensors depend on the conversion of light photons into electron hole pairs in the silicon substrate when they are exposed to light
Data Source
AI summary
A color image sensor includes an array of pixels arranged in a plurality of pixel groups, each pixel group including a floating diffusion that is shared by four pixels disposed in a 2×2 arrangement. Each of said four pixels includes a photodetector and a color filter superposed over the photodetector, wherein a first pair of said four pixels include green color, and a second pair of said four pixels includes either red or blue color filters. A control circuit controls the pixel groups such that discrete image information is generated from each pixel in normal light situations, and such that summed image information is generated from each pixel group in low light situations by simultaneously connecting the green pixels to the floating diffusion during a first time period, and simultaneously connecting the red/blue pixels to said floating diffusion during a second time period.