Photodiode Sensitivity Control for Flickering LED Detection
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Solution Overview
Problem
Image sensors struggle to accurately capture light levels from flickering light sources, such as LEDs, due to their limited ability to detect pulsed light with varying frequencies, leading to high contrast scenes with horizontal black strips and potential misdetection of light levels, particularly in automotive environments.
Innovation Solution
A method involving gradual variations in the sensitivity of photodiodes, including stepwise increases and decreases, and stabilization of sensitivity, along with adjustable sub-period durations, to integrate light levels and reduce flickering effects, allowing for continuous transition and improved detection accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the exposure period is adjusted to a multiple of the LED period to decrease flickering effect, then the flickering effect is reduced, but the device complexity increases due to the need to detect and adapt to varying LED frequencies
Solution Approach 1:
The patent changes the parameter of photodiode sensitivity gradually over time, creating a triangular sensitivity profile that increases to a maximum and then decreases. This parameter change allows the sensor to integrate light from flickering sources more effectively without requiring frequency detection or adjustment mechanisms, thus reducing device complexity while decreasing flickering effect.
Solution Approach 2:
The patent introduces dynamic variation in photodiode sensitivity during the exposure period, making the sensitivity time-dependent rather than constant. This dynamic approach allows the sensor to adapt to flickering light sources in real-time without requiring external frequency detection or adjustment mechanisms.
2Device complexity
If conventional image sensors are used with pulsed LEDs, then the sensor structure remains simple, but the measurement precision deteriorates due to high contrast scenes with horizontal black strips
Solution Approach 1:
The patent modifies the sensitivity parameter of the photodiode over time during the exposure period, creating a triangular sensitivity profile. This allows the sensor to capture light from pulsed LEDs more accurately by integrating light during periods when the LED is active, thereby improving measurement precision without complicating the sensor structure.
Solution Approach 2:
The patent employs periodic variation in photodiode sensitivity that aligns with the exposure period, creating a triangular sensitivity profile that repeats for each exposure. This periodic action enables the sensor to consistently capture light from flickering sources across multiple exposure cycles, improving measurement precision while maintaining a simple sensor structure.
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 effectively attenuates flickering effects, enhancing the accuracy of light level detection and making image sensors more robust to frequency deviations of flickering light sources, thereby improving image capture quality in environments with pulsed LEDs.
Implementation Method 1
a matrix array of pixels each including a photodiode and a control circuit that is suitable for delivering an output signal representative of the light level received by its photodiode
Data Source
AI summary
An image sensor includes a plurality of pixels, where each of the plurality of pixels includes a photodiode. The image sensor is configured to capture images of a scene exposed with a flickering light source by for each of the plurality of pixels, acquiring a value representative of a light level at a corresponding pixel by gradually varying a value of sensitivity of the corresponding pixel.