CMOS Image Sensor LED Flicker Mitigation via Dual Shutter Modes
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Solution Overview
Problem
Image sensors, particularly CMOS image sensors, face challenges in accurately capturing images of objects under LED lighting due to flickering, which can lead to incomplete object recognition and poor image quality.
Innovation Solution
The implementation of a CMOS image sensor with a pixel array and an ADC circuit that operates in two modes: a rolling shutter mode for LED environments to mitigate flicker and a global shutter mode for non-LED environments, allowing for synchronized photocharge accumulation and conversion across all pixel rows, enabling effective image capture under LED lighting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a mechanical shutter method is used to control exposure time, then the exposure time can be physically controlled, but the device complexity increases due to mechanical components
Solution Approach 1:
The patent replaces the mechanical shutter system with an electrical shutter method implemented in the CMOS image sensor. The exposure time is controlled electrically by controlling the integration time during which photocharges are generated and accumulated, eliminating the need for mechanical moving parts while achieving the same exposure control function.
2Ease of operation
If a rolling shutter method is used to control integration time in units of rows, then the integration time can be electrically controlled, but image quality deteriorates under LED lighting due to flicker
Solution Approach 1:
The patent applies periodic action by synchronizing the exposure timing with the LED flicker frequency. The integration time is set to be an integer multiple of the LED flicker period, ensuring that photocharges are accumulated during periods when the LED is emitting light, thereby eliminating flicker artifacts and improving image quality under LED lighting conditions.
3Ease of operation
If a global shutter method is used to control integration time uniformly across all rows, then the integration time can be uniformly controlled, but the ability to mitigate LED flicker is reduced
Solution Approach 1:
The patent implements a dynamic shutter method that combines elements of both rolling and global shutter approaches. The integration time is controlled uniformly across all rows (global shutter characteristic), but the timing is dynamically adjusted to synchronize with LED flicker cycles, enabling both uniform control and effective flicker mitigation by adapting the exposure timing to the periodic LED operation.
4Device complexity
If the image sensor operates in standard mode without LED flicker consideration, then the device complexity remains low, but object recognition accuracy deteriorates under LED lighting
Solution Approach 1:
The patent implements a dual-mode operating system that provides both standard operation and LED flicker mitigation modes. The image sensor can automatically detect LED lighting conditions and switch between operating modes, making the device universally applicable to both LED and non-LED environments without requiring separate dedicated hardware for each condition.
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 accurate object recognition and high-quality image capture even under flickering LED lighting conditions by adjusting the sensor's operating mode to account for LED flicker, improving image fidelity and frame rate.
Implementation Method 1
a first photoelectric conversion element operably connected to the floating diffusion node, and a second photoelectric conversion element operably connected to the floating diffusion node via the first photoelectric conversion element
Data Source
AI summary
Disclosed are an image sensor having a light-emitting diode (LED) flicker mitigation function and an image processing system including the image sensor. The image processing system includes an image sensor including a plurality of pixels, the plurality of pixels configured to respectively generate pixel signals corresponding to photocharges, and configured to perform analog-to-digital conversion (ADC) on the pixel signals to generate digital pixel signals; and an image signal processor configured to process the digital pixel signals to generate image data. The image sensor operates in a first operating mode in a situation in which a light-emitting diode (LED) light is provided, and operates in a second operating mode in a general situation in which the LED light is not provided.