Image Sensor Pixel Blocks with Shared Drains for Noise Reduction
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Solution Overview
Problem
Image sensors face challenges with noise generation and characteristic deterioration due to shared pixel structures, particularly temporal noise and fixed pattern noise, which arise from reduced pixel transistor sizes and differences in overlap capacitance and parasitic capacitance among unit pixels.
Innovation Solution
The design incorporates a pixel array with pixel blocks that share drains of reset and driver transistors alternately disposed in one direction, featuring a light receiving section with a floating diffusion and a driving section including reset and driver transistors, along with an intercoupling section that electrically couples the floating diffusion with the transistors, optimizing transistor sizes and reducing noise by ensuring equal overlap capacitance across unit pixels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If pixel transistor sizes are reduced to increase pixel density, then pixel array integration is improved, but temporal noise and fixed pattern noise increase
Solution Approach 1:
The pixel array is divided into multiple pixel blocks, where each block contains unit pixels that share a common floating diffusion region. This segmentation allows for larger effective transistor sizes within each block while maintaining high overall pixel density through the shared structure.
Solution Approach 2:
Adjacent pixel blocks share drains of reset transistors and driver transistors, merging common circuit elements across block boundaries. This merging reduces the total number of transistors needed while maintaining large effective transistor sizes, thereby reducing noise without sacrificing pixel density.
2Ease of manufacture
If pixel blocks are arranged with shared drains in a regular pattern, then manufacturing simplicity is improved, but fixed pattern noise increases due to capacitance differences
Solution Approach 1:
The patent employs two different pixel block types (first and second pixel blocks) with different internal arrangements of unit pixels around their respective floating diffusion regions. These asymmetric block types are alternately disposed in the pixel array, creating an overall symmetric pattern that balances capacitance values across the array while maintaining manufacturing simplicity.
Solution Approach 2:
Different regions of the pixel array contain different types of pixel blocks with locally optimized structures. The first pixel blocks have unit pixels arranged in one configuration, while second pixel blocks have unit pixels arranged in a different configuration, allowing each local region to be optimized for its specific position in the array to balance overall capacitance.
3Device complexity
If unit pixels share a common floating diffusion, then device complexity is reduced, but overlap capacitance and parasitic capacitance differences cause noise
Solution Approach 1:
The pixel array is segmented into multiple pixel blocks, each with its own floating diffusion region. This segmentation isolates the capacitance effects within each block, preventing cumulative capacitance differences across the entire array while still maintaining the benefits of shared floating diffusion within each block.
Solution Approach 2:
By using two different pixel block types with different internal arrangements and alternately disposing them, the patent creates a balanced overall structure where capacitance differences in one block type are compensated by the complementary structure of the other block type, effectively canceling out fixed pattern noise.
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 effectively prevents noise generation and characteristic deterioration by increasing pixel transistor sizes, reducing temporal and fixed pattern noise, and improving operational stability through balanced capacitance and voltage distribution.
Implementation Method 1
each unit pixel comprising a photoelectric conversion element that generates photocharges in response to incident light
Data Source
AI summary
An image sensor includes a pixel array including pixel blocks, each comprising a light receiving section including unit pixels sharing a floating diffusion; and a driving section including a reset transistor and a driver transistor, wherein the pixel blocks include a first pixel block and a second pixel block which are adjacent to each other in a first direction, and a third pixel block and a fourth pixel block which are adjacent to the first pixel block and the second pixel block, respectively, in a second direction, and wherein the reset transistor of the first pixel block and the reset transistor of the second pixel block share a drain between the reset transistors, and the driver transistor of the third pixel block and the driver transistor of the fourth pixel block share a drain between the driver transistors.