Storage-Gate Pixel Layout for High Dynamic Range Imaging
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Solution Overview
Problem
Conventional imager pixels have limited dynamic range and signal-to-noise ratio due to saturation and blooming issues, leading to incomplete light capture and fixed pattern noise, especially in scenes with varying light intensities.
Innovation Solution
The implementation of a pixel design with a shutter gate transistor, storage node, and anti-blooming transistor, which allows for multiple charge transfers during sub-integration periods, increasing the storage capacity and reducing fixed pattern noise by maintaining a constant anti-blooming gate voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional pixel design is used, then device complexity is low, but dynamic range is limited and saturation occurs easily
Solution Approach 1:
The pixel is divided into multiple functional regions: a photosensor for charge generation, a storage node for charge accumulation, a floating diffusion node for signal readout, and separate transistor gates (photogate, storage gate, transfer gate, anti-blooming gate) for independent control of each region. This segmentation allows multiple charge transfers during sub-integration periods, extending the dynamic range without requiring a larger pixel area.
2Adaptability or versatility
If pixel size is increased to extend saturation level, then dynamic range improves, but pixel area increases
Solution Approach 1:
The storage node is nested within the pixel structure, positioned between the photosensor and the floating diffusion node. The storage node acts as an intermediate charge accumulation region that can hold multiple times the charge capacity of a conventional pixel, effectively extending the saturation level without increasing the overall pixel footprint.
3Adaptability or versatility
If multiple charge transfers are implemented, then dynamic range increases, but fixed pattern noise increases
Solution Approach 1:
The anti-blooming transistor with its dedicated gate receives control signals to dynamically adjust the potential well depth in the photosensor region. This feedback mechanism prevents charge overflow and blooming effects that would otherwise create fixed pattern noise, while still allowing multiple charge transfers to extend the dynamic range.
Solution Approach 2:
The pixel employs multiple gates (photogate, storage gate, transfer gate, anti-blooming gate) that can independently modulate the potential landscapes in different regions. By changing the voltage parameters of these gates during sub-integration periods, the system can control charge transfer timing and prevent blooming, thereby reducing fixed pattern noise while maintaining extended dynamic range.
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 design enhances the light dynamic range and reduces fixed pattern noise, enabling a higher signal-to-noise ratio and extended saturation level without increasing pixel size, effectively capturing a broader range of light intensities.
Implementation Method 1
each cell includes a photo-conversion device, for example, a photogate, photoconductor or a photodiode overlying a substrate for producing a photo-generated charge in a doped region of the substrate
Data Source
AI summary
A method, apparatus and system are described providing a high dynamic range pixel. An integration period has multiple sub-integration periods during which charges are accumulated in a photosensor and repeatedly transferred to a storage node, where the charges are accumulated for later transfer to another storage node for output.