Segmented Pixel Image Sensor for Flicker Detection and Low Noise
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Solution Overview
Problem
Image sensors face increased noise and reduced signal-to-noise ratio (SNR) due to miniaturized pixel sizes, particularly when detecting light sources with flicker phenomena, such as LEDs, which affects their ability to accurately capture images in varying illuminance conditions.
Innovation Solution
The image sensor design incorporates multiple first photodiodes with a larger light-receiving area and a second photodiode with a smaller area, along with specific transistor configurations and microlenses, to enhance light detection and reduce noise. This includes dividing the first photodiode and its transfer transistor into multiple pieces to increase Full Well Capacity (FWC) and minimize charge movement, thereby reducing noise and improving SNR.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If pixel size is miniaturized to increase pixel density, then productivity and resolution are improved, but noise increases and signal-to-noise ratio deteriorates
Solution Approach 1:
The first photodiode is divided into multiple first photodiodes (e.g., four photodiodes) within a single pixel unit. Each photodiode has its own transfer transistor, and they share a common first floating diffusion region. This segmentation allows each photodiode to have sufficient light-receiving area while maintaining high pixel density through compact arrangement, thereby reducing noise and improving signal-to-noise ratio without sacrificing productivity.
2Reliability
If pixel size is increased to improve light-receiving area and reduce noise, then signal-to-noise ratio is improved, but pixel density and resolution deteriorate
Solution Approach 1:
Multiple first photodiodes and their transfer transistors are merged into a single pixel unit, sharing common floating diffusion regions and readout circuits. This merging allows the pixel to function as a unified sensing element with combined light-receiving area, achieving high signal-to-noise ratio while maintaining compact pixel dimensions for high density.
3Quantity of substance
If a single large photodiode is used to increase Full Well Capacity, then dynamic range is improved, but pixel area consumption increases and density decreases
Solution Approach 1:
The large photodiode is segmented into multiple smaller first photodiodes that collectively provide equivalent or greater Full Well Capacity through their combined area. The segmented structure fits within a compact pixel footprint, achieving high capacity without excessive area consumption.
Solution Approach 2:
Different regions within the pixel are assigned different functions: multiple first photodiodes are optimized for light reception and charge generation, while separate second photodiodes handle specific detection tasks. This local optimization allows efficient space utilization and high Full Well Capacity within limited pixel area.
4Adaptability or versatility
If multiple separate floating diffusion regions are used to process charges from multiple photodiodes, then charge processing capability is improved, but device complexity increases
Solution Approach 1:
Multiple first photodiodes share a common first floating diffusion region, and multiple pixels share second floating diffusion regions. This merging reduces the total number of floating diffusion regions and associated readout circuits, simplifying the device while maintaining the capability to process charges from multiple photodiodes through the shared infrastructure.
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
The solution effectively reduces noise and enhances the signal-to-noise ratio, allowing for accurate detection of flickering light sources and improved image quality across different illuminance levels, while preventing saturation of the second photodiode.
Implementation Method 1
Each of the plurality of pixels may include a photodiode generating an electric charge in response to external light
Data Source
AI summary
An image sensor includes a plurality of first photodiodes included in a first area of a unit pixel, and configured to generate electric charges, a second photodiode included in a second area of the unit pixel, and configured to generate electric charges, a first microlens disposed above the first area, a second microlens disposed above the second area, a first floating diffusion region included in the first area, a second floating diffusion region included in the second area, a plurality of first transfer transistors configured to provide the electric charges generated by the plurality of first photodiodes to the first floating diffusion region, and a second transfer transistor configured to provide the electric charges generated by the second photodiode to the second floating diffusion region. A sum of light-receiving areas of the plurality of first photodiodes is greater than a light-receiving area of the second photodiode.