Synchronized LED Driver for Rolling Shutter Imagers
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Solution Overview
Problem
CMOS imagers with rolling shutter exposure architecture face challenges with traditional PWM-controlled LED light sources, as they result in undesirable exposure regions due to asynchronous light exposure across lines, leading to image quality issues and safety concerns.
Innovation Solution
A lighting system with a drive circuit and lamp control circuit that synchronizes the LED light source with the horizontal line rate of the imager, using a line timing signal to energize the lamp in a pulse-width modulated manner, allowing for variable pulse width and PWM control to achieve exposures shorter than typical readout times without causing exposure effects in the video image.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If traditional PWM-controlled LED light sources are used with rolling shutter imagers, then light output intensity can be controlled, but undesirable exposure regions and motion distortion occur due to asynchronous light exposure across lines
Solution Approach 1:
The patent applies periodic action by synchronizing the LED light source pulsing with the horizontal line rate of the rolling shutter imager. The control circuit pulses the LED at the same frequency as the line exposure rate, ensuring that light is emitted during each line exposure period. This periodic synchronization eliminates the exposure uniformity problem while maintaining PWM intensity control capability.
2Duration of action of moving object
If PWM control is used to achieve variable pulse width for shorter exposures, then exposure duration can be reduced, but exposure variations and image quality issues arise without proper synchronization
Solution Approach 1:
The patent implements feedback by using the horizontal line timing signal from the imager as a reference input to the PWM control circuit. The control circuit receives this timing signal and uses it to synchronize the LED pulsing, ensuring that the variable pulse width is always aligned with the actual line exposure periods. This feedback mechanism maintains exposure control precision even with variable duration.
3Ease of operation
If frame-rate based PWM control is used, then light intensity control is simple, but it is unsuitable for rolling shutter imagers causing beating and flickering effects
Solution Approach 1:
The patent applies parameter changes by switching from frame-rate based PWM control parameters to line-rate based PWM control parameters. Specifically, the PWM frequency is changed to match the horizontal line rate, and the timing reference is changed from frame synchronization signals to line timing signals. This parameter change maintains control simplicity while eliminating the beating and flickering effects that occur with frame-rate control.
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 precise control of light output, reducing exposure variations and eliminating motion distortion, allowing for shorter exposure durations and improved image quality while maintaining safety by synchronizing the LED light source with the imager's line rate.
Implementation Method 1
the lamp control circuit synchronously energizing the lamp with the line timing signal via the drive circuit... energizing the lamp in a pulse-width modulated manner
Implementation Method 2
Adoption of high power Light-Emitting Diode (LED) technologies is becoming common in many fields and industries, including medical endoscopy
Data Source
AI summary
A lighting system adapted for use with a rolling shutter imagers. The system uniquely provides synchronous operation of a light source in the context of an imager with a “rolling-shutter”-type exposure architecture. The preferred embodiment comprises a lamp such as a LED, a drive circuit coupled to the lamp capable of energizing the lamp for switching the lamp on and off, and a lamp control circuit coupled to the drive circuit with a means for receiving a timing signal from an imaging system, the lamp control circuit synchronously energizing the lamp with the timing signal via the drive circuit, the timing signal being a line timing signal for a PWM system based on a multiple of lines, a signal indicating a pause in the imager readout, or a signal indicating a portion of the imager readout time when the lamp may safely be flashed on without corrupting the desired active imager lines.