Anti-blooming Shutter Control for CMOS Image Sensors
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Solution Overview
Problem
Conventional image sensors, particularly CMOS image sensors, suffer from blooming issues due to excess electron flow into adjacent pixels under high illumination, leading to decreased image quality, especially in shared pixel structures and electronic rolling shutter applications.
Innovation Solution
An anti-blooming shutter circuit that automatically recognizes exposure status of rows in the sensor and applies a shutter pulse to adjacent rows when they are not exposed, reducing blooming by selectively applying the anti-blooming shutter during non-integration time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If integration time is extended to capture more light in low illumination conditions, then image quality improves, but blooming risk increases due to continuous charge accumulation
Solution Approach 1:
The anti-blooming shutter is activated before the main integration period begins, preemptively emptying the photodiode of excess charge. This preliminary action prevents blooming during the subsequent integration time, allowing the system to safely extend integration time for improved light capture without the harmful effect of electron overflow into adjacent pixels.
2Object-affected harmful factors
If exposure time is shortened to avoid saturation under high illumination, then blooming is reduced, but image quality deteriorates due to insufficient light capture
Solution Approach 1:
The anti-blooming shutter opens before the main exposure period, pre-emptively removing excess charge that would cause saturation and blooming. This allows the integration time to be extended for improved light capture while the harmful blooming effect is prevented by the preliminary shutter action.
Solution Approach 2:
The anti-blooming shutter extracts or removes the harmful excess charge from the photodiode before it can overflow into adjacent pixels. By taking out the excess electrons during the non-integration time, the system can safely perform longer integration times without suffering from blooming artifacts.
3Productivity
If non-integration time is extended to allow charge transfer, then readout capability improves, but blooming risk increases due to continuous electron collection
Solution Approach 1:
The anti-blooming shutter is activated during the non-integration time period, preemptively emptying the photodiode before the next integration period begins. This preliminary action during NIT prevents continuous charge accumulation that would lead to saturation and blooming, while still allowing sufficient time for charge transfer and readout 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
Significantly reduces blooming effects across the image sensor, enhancing image quality by preventing electron overflow and saturation, even under varying illumination conditions without complex scanning schemes or hardware modifications.
Implementation Method 1
Each pixel includes a photo sensor that accumulates charge when illuminated by light
Implementation Method 2
the excess electrons may flow into adjacent pixels, which results in a halo effect around bright pixels
Data Source
AI summary
An image sensor includes a line driver, which further includes a transfer pulse generating circuit. The transfer pulse generating circuit is configured to determine an integration status of a first group of pixels, and to selectively apply the anti-blooming shutter to the first group of pixels based on the determined integration status of the first group of pixels.