Multi-Node Image Sensor Pixel for Wide Dynamic Range
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Solution Overview
Problem
Current image sensors face limitations in achieving a wide dynamic range and improved signal-to-noise ratio (SNR) due to the constraints of existing capacitor configurations connected to floating diffusion nodes.
Innovation Solution
The image sensor design incorporates a pixel array with multiple floating diffusion nodes and capacitors, including a third capacitor with a cylindrical shape to increase capacitance, allowing for efficient charge accumulation and overflow management across different conversion gain modes, thereby enhancing dynamic range and SNR.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a single floating diffusion node is used, then the device complexity is low, but the dynamic range is limited
Solution Approach 1:
The single floating diffusion node is segmented into multiple floating diffusion nodes (first, second, and third floating diffusion nodes), each capable of accumulating charges independently. This segmentation allows the pixel to handle a wider range of light intensities by distributing charge accumulation across multiple nodes, thereby expanding the dynamic range while managing device complexity through modular architecture
Solution Approach 2:
The patent implements dynamic switching between different floating diffusion nodes using switch transistors. The system can dynamically select which floating diffusion node to use based on the light intensity conditions, enabling adaptive operation across different illuminance levels. This dynamic allocation of charge accumulation resources optimizes the dynamic range without requiring all nodes to be permanently active, thus managing complexity
2Measurement precision
If multiple capacitors are added to increase dynamic range, then the signal-to-noise ratio is improved, but the device complexity increases
Solution Approach 1:
Multiple capacitors (first capacitor, second capacitor, third capacitor) are merged into a unified charge accumulation system where they can be selectively connected to different floating diffusion nodes. This merging approach allows the capacitors to work together as an integrated system for enhancing signal-to-noise ratio, rather than functioning as separate independent components, thereby managing overall device complexity
Solution Approach 2:
The capacitors are designed with multi-functionality, serving both as charge storage elements and as components that can be dynamically configured for different operating modes (high conversion gain, low conversion gain, ultra-low conversion gain). This universal design allows the same capacitor structure to fulfill multiple functions across different dynamic range requirements, improving signal-to-noise ratio without proportionally increasing complexity
3Quantity of substance
If multiple floating diffusion nodes are used, then charge accumulation capacity is improved, but the ease of manufacture decreases
Solution Approach 1:
Each floating diffusion node is designed with local quality optimizations, where the physical characteristics (such as area and capacitance) of each node are tailored to its specific function in the dynamic range. The first, second, and third floating diffusion nodes have different local properties optimized for different light intensity ranges, allowing efficient charge accumulation across the spectrum while using standardized fabrication processes for each local region
Solution Approach 2:
The multiple floating diffusion nodes and associated capacitors are arranged in a nested or hierarchical structure within the pixel area. The nodes are organized in a compact configuration where smaller functional units are nested within or adjacent to larger structures, allowing efficient space utilization. This nested arrangement increases charge accumulation capacity while maintaining manufacturability through systematic layout design
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 enables the generation of image data with a wide dynamic range and improved signal-to-noise ratio by effectively managing charges across high, low, and ultra-low conversion gain modes, resulting in higher quality image capture.
Implementation Method 1
Image sensors may generate an image of an object using a photoelectric conversion element that reacts according to the intensity of light reflected from the object
Data Source
AI summary
An image sensor includes a pixel array in which a plurality of pixels are arranged, wherein each of the pixels includes a photodiode, a transfer transistor, first to third floating diffusion nodes, a first capacitor, a second capacitor, a third capacitor, a first switch transistor, a second switch transistor, and a reset transistor. The second switch transistor is configured to turn off in a first period and to turn on in a second period of an exposure period of the photodiode, and the reset transistor is configured to turn on in the first period and to turn off in the second period of the exposure period of the photodiode.