CMOS Image Sensor Pixel Architecture with Shared Floating Diffusion
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Solution Overview
Problem
Conventional CMOS image sensors face challenges in reducing pixel size, increasing light collection efficiency, and minimizing fixed pattern noise while maintaining sensitivity and resolution.
Innovation Solution
The design incorporates a shared floating diffusion region and shared selection transistor in each column, with alternating patterns of photosensitive cell pairs and storage elements, along with a row selection logic that includes shift registers and combinational logic elements, allowing for efficient charge transfer and reduced pixel area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of moving object
If conventional CMOS image sensor designs are used, then device complexity is manageable, but pixel size cannot be reduced further and light collection efficiency is limited
Solution Approach 1:
The patent merges multiple functional elements within each pixel unit: photosensitive cells share floating diffusion regions, selection transistors, and amplifier circuits. This consolidation reduces the area required per pixel while distributing the complexity across shared resources that serve multiple pixels, thereby achieving pixel size reduction without proportionally increasing overall device complexity
Solution Approach 2:
The shared floating diffusion region and selection transistor serve multiple photosensitive cells simultaneously. A single selection transistor controls access to multiple pixels, and the shared amplifier processes signals from multiple pixels, making these components multi-functional and reducing the total component count per pixel area
2Manufacturing precision
If pixel size is reduced to increase resolution, then resolution improves, but light collection efficiency decreases
Solution Approach 1:
Multiple photosensitive cells share a common floating diffusion region, allowing the effective light collection area to be distributed across multiple cells while maintaining a compact pixel footprint. This enables smaller pixel dimensions for higher resolution while the combined photosensitive area of shared cells preserves light collection efficiency
Solution Approach 2:
The patent utilizes vertical stacking and multi-layer integration to separate light collection functions from signal processing functions. Photosensitive cells are arranged in configurations that maximize light capture area while sharing underlying circuitry, effectively adding dimensional efficiency to the pixel design
3Reliability
If more photosensitive elements are added to increase sensitivity, then sensitivity and dynamic range improve, but fixed pattern noise increases
Solution Approach 1:
Adjacent pixels share common circuit elements including floating diffusion regions, selection transistors, and amplifier circuits. This sharing equalizes the electrical characteristics across pixels, reducing variations in signal processing that manifest as fixed pattern noise, while maintaining high sensitivity through the combined photosensitive area
Solution Approach 2:
The shared circuit architecture ensures that all pixels within a shared group experience identical electrical conditions and processing paths. This homogenization of signal processing characteristics minimizes pixel-to-pixel variations and reduces fixed pattern noise while preserving sensitivity
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 approach reduces pixel size, enhances light collection efficiency, increases sensitivity and dynamic range, and improves resolution by 20%, while also reducing fixed pattern noise and simplifying the driving timing.
Implementation Method 1
each photosensitive cell further comprises a photodiode
Data Source
AI summary
An imaging apparatus is provided. The apparatus generally comprises an array and storage elements. The array includes photosensitive cells that are arranged in a plurality of columns and a plurality of rows such that each column includes a set of photosensitive cell pairs that have a shared region with a share floating diffusion region and a shared selection transistor. Also, the location of each shared region of each column is shifted by one row in each adjacent column.