Image Sensor Shifted Color Filter Array for Parallel Readout
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Solution Overview
Problem
Conventional image sensors face challenges in achieving high full well capacity and increased readout speed due to the limitations of reading out signals from 4C cells, which typically require trading off between photodiode full well capacity and conversion gain, or slowing down image sensor speed by reading out signals separately in time.
Innovation Solution
A shifted color filter array pattern is implemented, allowing four neighboring photodiodes of the same color to be read out using two floating diffusions instead of one, thereby achieving high full well capacity and increased readout speed by enabling simultaneous readout of all four photodiodes in a single read period.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If signals from four neighboring photodiodes are read out using a single floating diffusion, then device complexity is reduced, but full well capacity and readout speed are limited
Solution Approach 1:
The patent divides the readout function by implementing separate floating diffusions for different color channels (e.g., first floating diffusion for red photodiodes, second floating diffusion for green photodiodes). This segmentation allows parallel readout of multiple photodiodes without requiring a single complex floating diffusion, thereby increasing readout speed while maintaining manageable device complexity.
Solution Approach 2:
The patent introduces a new dimension to the readout architecture by adding multiple floating diffusions operating in parallel rather than using a single floating diffusion. This dimensional expansion in the readout path enables simultaneous readout of multiple photodiodes, resolving the trade-off between complexity and productivity.
2Quantity of substance
If photodiode full well capacity is increased, then more charge can be stored, but conversion gain decreases
Solution Approach 1:
By segmenting the charge collection into multiple specialized floating diffusions (one for each color channel), each floating diffusion can be optimized for its specific function. This allows the photodiodes to maintain high full well capacity while the segmented floating diffusions preserve conversion gain through dedicated charge collection paths for each color.
Solution Approach 2:
The patent applies local quality by assigning different floating diffusions to different color channels, allowing each region of the readout circuit to have optimized properties for its specific color. This localized optimization enables simultaneous high full well capacity in photodiodes and high conversion gain in the specialized floating diffusions.
3Quantity of substance
If signals are read out separately in time, then full well capacity can be maintained, but readout speed decreases
Solution Approach 1:
The patent merges the readout capability across multiple floating diffusions to enable simultaneous readout of multiple photodiodes in a single read period. By combining the readout functions of multiple floating diffusions operating in parallel, the system achieves both high full well capacity and high readout speed, eliminating the need for sequential readout.
Solution Approach 2:
The patent implements continuous useful action by enabling all photodiodes to be read out simultaneously in parallel through multiple floating diffusions, rather than sequentially. This continuous parallel operation maintains high full well capacity while maximizing readout speed, as all charge collection and readout actions occur concurrently without temporal separation.
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 enhances the full well capacity and readout speed of image sensors by allowing simultaneous readout of all four photodiodes of the same color, improving the overall performance and efficiency of image acquisition.
Implementation Method 1
The image sensor includes an array of pixels having photosensitive elements (e.g., photodiodes) that absorb a portion of the incident image light and generate image charge upon absorption of the image light
Data Source
AI summary
An imaging device includes groupings of photodiodes having four photodiodes. A transfer transistor is between each photodiode and a floating diffusion. Each floating diffusion is coupled to up to two photodiodes per grouping at a time through transfer transistors. A buffer transistor is coupled to each floating diffusion. The buffer transistors may be in a first or second grouping of buffer transistors. A first bit line is coupled to up to two buffer transistors of the first grouping and a second bit line is coupled to up to two buffer transistors of the second grouping of buffer transistors at a time. A color filter array including a plurality of groupings of color filters is disposed over respective photodiodes of the photodiode array, wherein each grouping of color filters includes four color filters having a same color, wherein each grouping of color filters overlaps two groupings of photodiodes.