8-Shared Pixel Structure for Image Sensor Noise Reduction
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Solution Overview
Problem
High-resolution image sensors with shared pixel structures face challenges in maintaining high performance due to reduced transistor areas, leading to operational degradation and uneven pixel characteristics, as well as issues with parasitic capacitance and temporal noise.
Innovation Solution
The design includes a pixel array with a shared pixel structure where multiple unit pixels share a floating diffusion, and driving circuits are positioned to maximize transistor sizes within a limited area, with parallel coupling structures for driver and selection transistors, and symmetrical intercoupling circuits to minimize variations and noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If multiple unit pixels share a floating diffusion to achieve high integration, then device complexity is reduced and area is saved, but transistor areas are reduced leading to operational degradation and uneven pixel characteristics
Solution Approach 1:
The pixel array is divided into multiple pixel blocks, each containing a specific number of unit pixels (e.g., 2x2, 4x4) that share a common floating diffusion. This segmentation allows the patent to optimize the sharing ratio to balance area efficiency with sufficient transistor area for reliable operation.
Solution Approach 2:
The patent applies different floating diffusion sharing configurations to different regions of the pixel array. By optimizing the sharing ratio locally in each pixel block, the patent maintains uniform pixel characteristics while achieving high overall integration, addressing the operational degradation issue.
2Productivity
If transistor areas are reduced in shared pixel structures, then more pixels can be integrated, but current driving force decreases and noise resistance deteriorates
Solution Approach 1:
The patent employs parallel coupling structures for driver transistors and selection transistors that can dynamically adjust their effective width. This allows the circuit to maintain sufficient current driving force by utilizing multiple transistors working in parallel, compensating for the reduced individual transistor area while achieving high integration density.
Solution Approach 2:
Multiple transistors are merged in parallel configurations within each pixel block. The driver transistors and selection transistors are coupled in parallel to collectively provide the necessary current driving force and noise resistance, enabling high integration without sacrificing power performance.
3Power
If driving circuits are positioned to maximize transistor sizes, then current driving force is improved, but area utilization efficiency decreases
Solution Approach 1:
The patent positions driving circuits at the periphery of pixel blocks rather than within the central pixel array area. By utilizing the boundary regions and arranging circuits in parallel configurations along the edges, the patent maximizes transistor sizes for sufficient current driving force while minimizing the impact on overall pixel block area utilization.
4Area of stationary object
If parasitic capacitance is reduced through miniaturization, then area is saved, but temporal noise increases
Solution Approach 1:
Multiple transistors are merged in parallel configurations, which increases the total effective area for signal processing. This merging effect helps reduce the relative impact of parasitic capacitance and temporal noise by distributing the signal across multiple devices, thereby maintaining low noise performance despite circuit miniaturization.
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 configuration enhances the current driving force and noise resistance of the image sensor while maintaining high-resolution imaging, ensuring uniform operation characteristics across unit pixels.
Implementation Method 1
each pixel block may include a first photodiode that generates first photocharges in response to incident light and a second photodiode that generates second photocharges in response to incident light
Data Source
AI summary
An image sensor includes a first pixel group and a second pixel group positioned adjacent to the first pixel group. The first pixel group includes a first light receiving circuit and first and second driving circuits formed adjacent to one end of the first light receiving circuit. The first light receiving circuit includes a plurality of unit pixels sharing a first floating diffusion. The second pixel group includes a second light receiving circuit and third and fourth driving circuits formed adjacent to one end of the second light receiving circuit. The second light receiving circuit includes a plurality of unit pixels sharing a second floating diffusion. The first driving circuit is coupled in parallel to the third driving circuit, and the second driving circuit is coupled in parallel to the fourth driving circuit.