Global Shutter Sensor Parasitic Light Mitigation
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Solution Overview
Problem
Global shutter image sensors face challenges with parasitic light sensitivity, which degrades images, especially at very fast exposure times, limiting their use in capturing motion-free images in outdoor and large area applications with uncontrolled lighting.
Innovation Solution
An imaging device combining a global shutter image sensor with a mechanical shutter, where the control system synchronizes the image sensor and the shutter to ensure the shutter closes before the readout of light-shielded storage units begins, effectively blocking parasitic light.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If global shutter image sensors are used to achieve ultra-short exposure times, then motion blur is reduced, but parasitic light sensitivity degrades image quality
Solution Approach 1:
A mechanical shutter is introduced as an intermediary component between the lens and the global shutter image sensor. The mechanical shutter physically blocks parasitic light from reaching the sensor during readout operations, while allowing full light transmission during the ultra-short exposure period. This mediator resolves the contradiction by selectively controlling light access based on operational phase.
Solution Approach 2:
The mechanical shutter closes before the readout phase begins, preemptively blocking parasitic light before it can contaminate the image data. By performing this protective action in advance, the system ensures that when readout occurs, no parasitic light can reach the sensor, thus eliminating image degradation while maintaining ultra-short exposure capability.
2Object-affected harmful factors
If mechanical shutter closing speed is increased to block parasitic light faster, then parasitic light sensitivity is reduced, but shutter lifetime is reduced
Solution Approach 1:
The mechanical shutter is designed to close before the readout phase begins, rather than during readout. This preliminary closing action blocks parasitic light effectively while allowing the shutter to operate at slower, more durable speeds. The timing strategy separates the shutter's protective function from the readout operation, enabling extended shutter lifetime.
Solution Approach 2:
The mechanical shutter closes slightly earlier than the minimum required time, providing a timing margin that ensures complete blockage of parasitic light. This excessive timing action guarantees that even with slower closing speeds, the shutter achieves sufficient blockage before readout begins, maintaining image quality while extending shutter operational life.
3Object-affected harmful factors
If mechanical shutter is used to block parasitic light, then image quality is improved, but device complexity increases
Solution Approach 1:
The mechanical shutter serves multiple functions: it blocks parasitic light during readout, maintains ultra-short exposure times, and can be synchronized with the global shutter sensor's operation cycles. By designing the shutter control system to integrate with existing sensor timing, the patent achieves multi-functionality that justifies the added complexity through enhanced versatility.
Solution Approach 2:
The control system synchronizes the mechanical shutter's closing action with the sensor's readout phase by monitoring timing signals. This feedback-based synchronization ensures that the shutter closes at the precise moment needed to block parasitic light, coordinating the additional mechanical component with the electronic sensor operations to maintain system efficiency.
4Object-affected harmful factors
If exposure time is extended to allow mechanical shutter to close, then parasitic light is blocked, but motion blur increases
Solution Approach 1:
The patent segments the image capture process into distinct phases: an ultra-short exposure phase for capturing motion-free images, followed by a readout phase during which the mechanical shutter blocks parasitic light. This segmentation allows the exposure time to remain extremely short for image quality, while the shutter operates during the separate readout phase to eliminate parasitic light contamination.
Solution Approach 2:
The mechanical shutter closes before the readout phase begins, preparing the system in advance to block parasitic light. This preliminary action ensures that when readout occurs, the shutter is already in position, eliminating the need to extend exposure time and maintaining ultra-short exposure capability while still achieving complete parasitic light blockage.
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 solution enables the use of ultra-short exposure times without streaks from parasitic light, extends the lifetime of mechanical shutters by operating them at slower speeds, and allows for larger aperture lenses, facilitating high-quality image capture in challenging conditions.
Implementation Method 1
a global shutter image sensor having an array of photoelectric conversion units and light-shielded storage units
Implementation Method 2
a shutter having an open state in which it allows incoming light to reach the image sensor and a closed state in which it prevents incoming light to reach the image sensor
Data Source
AI summary
In global shutter image sensors, the light shields are often not completely lightproof and incoming light causes continued exposure even after the global shutter is shut. This ‘parasitic light’ degrades the recorded image. Disclosed is a method, performed by an imaging device with a global shutter image sensor, for recording an image with reduced degrading effects from parasitic light in the image sensor. The disclosed device and related method combine the global shutter functionality of the global shutter image sensor with a shutter such as a mechanical shutter. A precise synchronization of the closing of the shutter means that the shutter can block all incoming light—and thus stop parasitic light in the image sensor—shortly after the exposure is stopped by the global shutter image sensor. This allows the imaging device to record very short exposure images without the detrimental effects of parasitic light.