Shared-FD Image Sensor Readout for Resolution and Low-Light SNR
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Solution Overview
Problem
Image sensors struggle to capture high-quality images in both bright and dark scenes, failing to balance resolution and signal-to-noise ratio effectively.
Innovation Solution
The image sensor employs a pixel array with shared floating diffusion regions and multiple sub-pixels per pixel, combined with conversion circuits that can switch between full-resolution and primary merging output modes to optimize image capture based on lighting conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the image sensor uses a conventional pixel structure with one photoelectric conversion element per pixel, then the circuit complexity is low, but the image quality in dark scenes deteriorates due to insufficient light capture
Solution Approach 1:
Each pixel is divided into multiple sub-pixels (e.g., 4 sub-pixels), each with its own photoelectric conversion element. This segmentation allows the pixel to capture light from multiple independent elements, improving signal-to-noise ratio in dark scenes while maintaining manageable circuit complexity through shared readout circuitry
Solution Approach 2:
Multiple sub-pixels within a pixel share common circuit components including the floating diffusion region, transfer transistor, and readout circuitry. This merging approach improves dark scene performance by combining signals from multiple photoelectric conversion elements while avoiding the complexity of completely independent circuits for each sub-pixel
2Reliability
If the image sensor increases the number of photoelectric conversion elements per pixel to improve dark scene performance, then the signal-to-noise ratio improves, but the manufacturing precision requirements increase
Solution Approach 1:
The pixel is segmented into multiple sub-pixels with regular, repeating structures that can be manufactured using standard photolithography processes. The segmented design with shared circuitry reduces the precision requirements compared to completely independent pixel structures, as the common components can be fabricated with relaxed tolerances
Solution Approach 2:
The invention changes the structural parameters of the pixel by introducing multiple sub-pixels with specific geometric arrangements and shared circuit configurations. These parameter changes optimize the balance between signal-to-noise ratio and manufacturability by leveraging standard fabrication capabilities while achieving improved performance
3Reliability
If the image sensor uses multiple sub-pixels per pixel to improve resolution, then the image quality in bright scenes improves, but the device complexity increases due to multiple conversion circuits
Solution Approach 1:
Multiple sub-pixels share common circuit components including the floating diffusion region, transfer transistor, and readout circuitry. This merging reduces device complexity by eliminating redundant circuits while maintaining the resolution benefits of multiple photoelectric conversion elements
Solution Approach 2:
The shared circuit components serve multiple functions: the floating diffusion region collects charges from all sub-pixels, the transfer transistor manages charge transfer for multiple photoelectric conversion elements, and the readout circuitry processes signals from the entire pixel. This multi-functionality reduces overall device complexity while maintaining high-resolution capability
4Adaptability or versatility
If the image sensor implements both full-resolution and primary merging output modes, then the adaptability to different lighting conditions improves, but the device complexity increases
Solution Approach 1:
The readout circuit is designed with dynamic switching capability that allows it to operate in different modes (full-resolution mode and primary merging mode) based on lighting conditions. The circuit can dynamically reconfigure its operation without requiring physically separate circuit paths, achieving adaptability while controlling complexity through a single reconfigurable circuit 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 design enables high-resolution, high-signal-to-noise ratio images in bright scenes and high-quality images in dark scenes by adaptively adjusting output modes, enhancing overall image quality across varying lighting conditions.
Implementation Method 1
each of the plurality of pixels comprises a pixel circuit arranged with a plurality of output ends, the pixel circuit comprises a plurality of photoelectric conversion elements in one-to-one correspondence with the plurality of sub-pixels; the pixel circuit is configured to transfer charges, which are generated by at least one of the plurality of photoelectric conversion elements
Data Source
AI summary
An image sensor includes: a pixel array, the pixel array including a plurality of pixels, and each pixel including a plurality of sub-pixels, wherein the sub-pixels in a same pixel share a same floating diffusion region (FD); each pixel including a pixel circuit provided with a plurality of output ends, and the pixel circuit being used for transferring charges generated by at least one photoelectric conversion element in a same pixel to the FD for accumulation, and selecting at least one output end to output analog signals corresponding to the charges in the FD; and a plurality of first conversion circuits, each first conversion circuits being used for performing analog-to-digital conversion on each analog signal outputted by a same pixel circuit, and reading a converted digital signal together with the pixel circuit on the basis of a full-resolution output mode or a first-stage combined output mode.