Image Sensor Pixel Layout for LED Flicker-Free Capture
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Solution Overview
Problem
Conventional semiconductor image sensors experience flickering effects when capturing light from pulsing LED sources due to mismatched operating frequencies, leading to incomplete or inaccurate image capture, which can be visually displeasing and pose safety risks in applications like automotive systems.
Innovation Solution
The implementation of 'small' pixels with lower quantum efficiency than standard pixels, along with a microcontroller that controls their on and off times, ensures that at least one pixel is always active to capture LED light, reducing or eliminating the flickering effect by extending the integration time without overexposure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If standard pixels are used with conventional on/off cycling, then image capture is efficient for steady light sources, but flickering occurs when capturing pulsing LED light due to frequency mismatch
Solution Approach 1:
The pixel array is divided into multiple independently controllable pixel groups, each capable of being activated at different times. This segmentation allows the system to capture light from pulsing LED sources by activating different pixel groups during different phases of the LED pulse cycle, thereby eliminating flickering while maintaining efficient image capture for steady light sources.
2Reliability
If pixels are turned on continuously to capture all LED light, then flickering is reduced, but overexposure occurs with steady light sources
Solution Approach 1:
The system employs periodic activation of pixel groups synchronized with the expected pulse frequency of LED sources. By activating pixel groups in periodic intervals rather than continuously, the system captures sufficient LED light to eliminate flickering while preventing overexposure during steady light conditions through controlled exposure timing.
3Reliability
If pixel on/off frequency is increased to match high-frequency LED pulsing, then flickering is reduced, but power consumption increases
Solution Approach 1:
By segmenting the pixel array into multiple groups that can be activated sequentially rather than simultaneously, the system reduces the total number of pixels active at any given moment. This segmentation allows the system to match high-frequency LED pulsing effectively while minimizing overall power consumption through reduced simultaneous pixel activation.
Solution Approach 2:
The system activates only the necessary subset of pixel groups required to capture the pulsing LED light, rather than activating all pixels continuously. This partial action approach achieves effective flickering reduction by capturing sufficient light during pulse periods while significantly reducing power consumption compared to full-array continuous activation.
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 effectively reduces or eliminates the flickering effect, ensuring accurate image capture and enhancing safety in applications like self-driving vehicles by ensuring continuous capture of LED light, even when standard pixels miss the pulsing frequency.
Implementation Method 1
These devices utilize an array of pixels (which may include photodiodes and transistors) in a substrate to absorb (i.e., sense) radiation that is projected toward the substrate and convert the sensed radiation into electrical signals.
Data Source
AI summary
An image sensor device has a first number of first pixels disposed in a substrate and a second number of second pixels disposed in the substrate. The first number is substantially equal to the second number. A light-blocking structure disposed over the first pixels and the second pixels. The light-blocking structure defines a plurality of first openings and second openings through which light can pass. The first openings are disposed over the first pixels. The second openings are disposed over the second pixels. The second openings are smaller than the first openings. A microcontroller is configured to turn on different ones of the second pixels at different points in time.