Image Sensor Pixel Structure with Homogeneous Transistor Layout
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Solution Overview
Problem
The effective image resolution of CMOS image sensors is affected by the difference in sensitivity between green (Gb) and green (Gr) active pixels due to geometric and time-domain non-uniformities introduced by current pixel structures, leading to errors in interpolation and reduced resolution.
Innovation Solution
The image sensor design includes a series of 2×2 Bayer-pattern units with photodiodes arranged diagonally, where the transistors associated with each photodiode have identical positions and orientations, and the outputs of paired photodiodes share a common floating drain, allowing for improved geometric and time-domain uniformity, and enabling selective access to reduce the number of processing circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional pixel structures with different transistor positions and orientations are used for Gb and Gr pixels, then device layout flexibility is improved, but sensitivity uniformity deteriorates
Solution Approach 1:
The patent applies homogeneity by making the transistor positions and orientations identical for both Gb and Gr pixels within each 2x2 Bayer-pattern unit. This ensures that both green pixels have the same geometric relationship with their associated transistors, eliminating sensitivity differences caused by structural asymmetry while maintaining layout flexibility through the standardized unit design.
Solution Approach 2:
The patent segments the pixel array into repeating 2x2 Bayer-pattern units, where each unit contains a standardized configuration of photodiodes and transistors. This segmentation allows the uniformity principle to be applied consistently across the entire sensor while maintaining overall layout flexibility through the modular repeating structure.
2Device complexity
If different access timing is used for Gb and Gr pixels, then processing circuit complexity is reduced, but time-domain uniformity deteriorates
Solution Approach 1:
The patent applies homogeneity by implementing identical access timing sequences for both Gb and Gr pixels. The control signals enable both green pixels to be accessed in the same temporal pattern, ensuring time-domain uniformity while maintaining processing efficiency through the regular, repeating access pattern across the pixel array.
3Measurement precision
If more processing circuits are used to handle individual pixel outputs, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent merges the output processing by having multiple photodiodes within each 2x2 unit share common readout circuitry. The standardized configuration allows adjacent pixels to use shared transistors and output nodes, reducing the total number of processing circuits while maintaining measurement precision through the uniform geometric and temporal characteristics of the pixel units.
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 design reduces the Gb-Gr difference in sensitivity, enhances image resolution by improving geometric and time-domain uniformity, and decreases the number of processing circuits required, resulting in more accurate and efficient image capture.
Implementation Method 1
The active pixels can sense the filtered light going through the color filter
Data Source
AI summary
An image sensor includes at least a first row and a second row of photodiodes, each photodiode being coupled with an associated transistor, each associated transistor including a gate, the first and second row of photodiodes forming a series of 2×2 Bayer-pattern units. In each Bayer-pattern unit, a first photodiode and a second photodiode in the first row are designated respectively as a first green pixel and a blue pixel, and a third photodiode and a fourth photodiode in the second row are designated respectively as a red pixel and a second green pixel, wherein a position of the gate of the transistor associated with the first photodiode relative to the first photodiode and a position of the gate of the transistor associated with the fourth photodiode relative to the fourth photodiode are the same.