White-Pixel Image Sensor Layout for Low-Light and Saturation Control
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Solution Overview
Problem
Current image sensors face challenges in achieving high sensitivity and resolution while minimizing the area of each pixel, as increasing pixel size leads to a larger sensor volume, and existing methods do not effectively address the issue of pixel saturation in varying illuminance environments.
Innovation Solution
The image sensor incorporates a pixel array with a higher number of white pixels than color pixels, where each pixel group includes a color pixel and surrounding white pixels, allowing for improved sensitivity in low illuminance environments and switching to color pixel signal acquisition in high illuminance to prevent saturation, using a remosaic method to maintain image quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the number of white pixels is increased to improve sensitivity in low illuminance environments, then sensitivity is improved, but the pixel area for color pixels decreases, worsening resolution
Solution Approach 1:
The pixel array is segmented into color pixels and white pixels with different functions. Color pixels (with red, green, blue filters) are responsible for color information and resolution, while white pixels (without color filters) are dedicated to sensitivity in low light. This segmentation allows each pixel type to optimize its specific function without compromising the other.
Solution Approach 2:
Different regions of the pixel array have different local qualities: color pixels are positioned where color accuracy and resolution are priorities, while white pixels are positioned where sensitivity is critical. The pixel circuit is designed to selectively read out from color or white pixels based on illuminance conditions, applying local quality optimization to different spatial and operational contexts.
2Reliability
If photodiode area is increased to improve sensitivity, then sensitivity is improved, but pixel area increases, worsening device compactness
Solution Approach 1:
The pixel circuit is designed with multi-functionality to handle both color pixels and white pixels. The same pixel circuit structure can read out signals from either type of pixel, and the readout path can be dynamically configured. This universality allows the system to achieve high sensitivity through white pixels without requiring larger pixel areas, as the circuit efficiently utilizes the available space for both pixel types.
3Speed
If all pixels are used for reading in high illuminance environments, then data acquisition speed is improved, but image quality degrades due to photodiode saturation
Solution Approach 1:
The pixel circuit incorporates dynamic switching capability that adapts to illuminance conditions. In high illuminance environments, the circuit dynamically selects to read only from color pixels, avoiding saturation issues. In low illuminance environments, it switches to read from white pixels for maximum sensitivity. This dynamic adaptation allows the system to optimize both speed and image quality based on real-time lighting conditions.
Solution Approach 2:
The system changes operational parameters based on illuminance levels. The readout configuration parameter is adjusted: in high illuminance, only color pixels are activated for reading; in low illuminance, white pixels are activated. This parameter change allows the system to prevent photodiode saturation while maintaining data acquisition efficiency.
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 sensitivity and image quality in low light conditions while preventing pixel saturation in high light environments, allowing for high-resolution imaging with reduced pixel area and sensor volume.
Implementation Method 1
Each of the plurality of pixels includes at least one photodiode
Data Source
AI summary
An image sensor includes a pixel array with pixels arranged in a first direction and a second direction, intersecting the first direction. Each of the pixels includes a photodiode, a pixel circuit below the photodiode, and a color filter on or above the photodiode. A logic circuit acquires a pixel signal from the pixels through a plurality of column lines extending in the second direction. The pixels include color pixels and white pixels, the number of white pixels being greater than the number of color pixels. The pixel circuit includes a floating diffusion in which charges of the photodiode are accumulated and transistors outputting a voltage corresponding to amounts of charges in the floating diffusion. Each of the color pixels shares the floating diffusion with at least one neighboring white pixel, adjacent thereto in the second direction, among the white pixels.