Multiresolution Imager Pixel Binning for Low-Noise Night Vision
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Solution Overview
Problem
Existing imaging sensors, such as CMOS-based quad pixel imagers, face challenges with high read noise due to large sense nodes required for charge transfer from multiple photodiodes, which affects low light level sensitivity and dynamic range.
Innovation Solution
The implementation of a multiresolution imager with a pixel architecture that includes multiple photodiodes, a common region for charge binning, and a read gate to transfer charge to a sense node, allowing for simultaneous charge binning from multiple photodiodes during integration time, reducing read noise and increasing dynamic range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a large sense node is used to directly receive charge from multiple photodiodes, then the pixel can accumulate sufficient charge signal, but the read noise increases due to higher capacitance
Solution Approach 1:
The pixel structure is segmented into multiple independent photodiodes (e.g., four photodiodes) that can be independently controlled and transferred. This segmentation allows selective binning of charge from multiple photodiodes into a common region, accumulating sufficient charge signal while maintaining lower capacitance per photodiode compared to a single large photodiode design.
Solution Approach 2:
A common region is introduced as an intermediary between the multiple photodiodes and the sense node. This common region acts as a charge accumulation buffer, receiving charge from multiple photodiodes through transfer gates and then transferring the combined charge to the sense node. This intermediary structure enables charge binning without requiring the sense node to directly interface with all photodiodes, thereby managing capacitance and noise more effectively.
2Adaptability or versatility
If sequential charge transfer through multiple transfer gates is used, then charge can be transferred from multiple photodiodes, but the sense node capacitance increases and read noise increases
Solution Approach 1:
The charge transfer path is segmented into multiple independent transfer gates, each associated with a specific photodiode. This segmentation allows flexible control over which photodiodes contribute charge to the common region, enabling adaptive binning strategies while minimizing the cumulative capacitance effect on the sense node compared to direct connections.
Solution Approach 2:
The common region serves as an intermediary charge holding area that decouples the multiple transfer gates from the sense node. Charge from multiple photodiodes is transferred to this intermediate region first, and then a single transfer operation moves the combined charge to the sense node. This reduces the number of direct coupling paths between transfer gates and the sense node, thereby reducing total capacitance and read noise.
3Reliability
If multiple photodiodes are integrated into a single pixel architecture, then sensitivity and dynamic range are enhanced, but the device complexity increases
Solution Approach 1:
The pixel architecture is designed with universal components that serve multiple functions: the common region can hold charge from any combination of photodiodes, the transfer gates can selectively transfer charge from different photodiodes, and the sense node can read out the combined signal. This multi-functionality allows the same structural elements to handle various binning configurations (e.g., 1x1, 2x2, 4x1) without requiring additional dedicated components for each mode, thereby managing complexity while enhancing sensitivity and dynamic range.
4Object-affected harmful factors
If a rolling shutter process is used for charge binning, then read noise is reduced through simultaneous charge collection, but the imaging process becomes more complex
Solution Approach 1:
The rolling shutter process implements preliminary charge collection and binning in the common region before the readout operation. By simultaneously collecting charge from multiple photodiodes during the integration period and pre-binning it in the common region, the system prepares the charge signal in advance, reducing the need for complex post-readout processing and minimizing read noise through coordinated simultaneous transfer operations.
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 read noise and enhances low light level sensitivity and dynamic range by using charge binning in a common region, enabling detection in low light conditions with reduced geometric distortion and improved noise levels.
Implementation Method 1
An image sensor has a set of pixels making up the image sensor to capture an image. Two or more pixels in the set of pixels each have an architecture that includes multiple photodiodes... Each photodiode can have a transfer gate electrically coupled to that photodiode.
Implementation Method 2
A common region can hold or transfer charge at least during or after an integration time. A read gate electrically coupled to the common region and a sense node can supply charge from the common region through the read gate to the sense node.
Data Source
AI summary
An image sensor having a set of pixels making up the image sensor to capture an image. Two or more pixels in the set of pixels each have an architecture that includes multiple photodiodes configurable to form an individual pixel. A control system can cooperate with the multiple photodiodes to form the individual pixel. Each of the multiple photodiodes can have a transfer gate electrically coupled to that photodiode. A common region can hold or transfer charge at least during or after an integration time. A read gate electrically coupled to the common region and a sense node, can supply charge from the common region through the read gate to the sense node.