Image Sensor Shared Node for Low-Light Noise Reduction
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Solution Overview
Problem
CMOS image sensors face limitations in achieving low-light performance with reduced noise, particularly in applications requiring high-speed image capture and motion artifact minimization, as existing shutter modes and binning techniques are not optimized for simultaneous operation.
Innovation Solution
The implementation of an image sensing circuit with a shared node that allows pixels to combine their outputs in the charge domain, enabling both pipeline and global shutter modes while enhancing low-light performance through binning, thereby reducing noise and improving image capture efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If pixels use traditional separate readout circuits, then each pixel can be read independently, but the device complexity increases and low-light performance deteriorates due to higher noise levels
Solution Approach 1:
Multiple pixel readout circuits share a common floating diffusion node and readout amplifier, combining previously separate circuits into a shared infrastructure. This reduces overall device complexity while enabling binning operations that improve low-light performance by summing charges from multiple pixels at the shared node before amplification and readout.
2Productivity
If pixels operate in pipeline shutter mode for high-speed capture, then frame rate increases, but motion artifacts increase compared to global shutter mode
Solution Approach 1:
The shared floating diffusion node dynamically switches between receiving charges from different pixels at different times, enabling the system to adapt between pipeline shutter mode (higher frame rate) and global shutter mode (lower motion artifacts) by controlling the timing and sequence of charge transfers to the shared node.
3Measurement precision
If pixels are binned together to reduce noise, then low-light performance improves, but the ability to resolve fine spatial details decreases
Solution Approach 1:
The shared readout circuit enables dynamic binning where pixels can be selectively combined or kept separate based on scene requirements. The system can switch between binned mode (improving low-light performance by summing charges at the shared node) and unbinned mode (preserving spatial resolution) without requiring separate hardware paths.
4Speed
If each pixel has its own dedicated readout circuit, then readout speed is maximized, but power consumption increases and device area expands
Solution Approach 1:
Multiple pixels share a common readout amplifier and floating diffusion node, reducing the total number of active circuit elements. This sharing approach reduces power consumption while maintaining high readout speed through the shared high-performance readout path, and reduces the area required for readout circuitry compared to fully dedicated circuits for each pixel.
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 enables CMOS image sensors to achieve high-speed image capture with reduced motion artifacts and enhanced low-light performance by allowing pixels to operate in multiple shutter modes and binning configurations, resulting in improved image quality and noise reduction.
Implementation Method 1
a first pixel comprising a first photo diode... a second pixel comprising a second photo diode
Data Source
AI summary
In accordance with an embodiment of the present invention, an image sensor comprises a plurality of pixel sensing circuits. Each pixel sensing circuit includes a photodiode and a storage node. Each pixel sensing circuit further includes a first transistor coupled between the photodiode and the storage node and a second transistor coupled between the photodiode and a shared node. The shared node is coupled to the plurality of pixel sensing circuits. The image sensor may include a reset transistor and/or a read-out circuit coupled to the shared node.