Dynamic Scanning Backlight Color Control Loop
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Solution Overview
Problem
Existing LED backlighting systems for LCD matrix displays face challenges in motion blur due to finite response time and lack of contrast, especially in ambient light, as they cannot rapidly adjust color balance and luminance on a frame-by-frame basis, leading to suboptimal image quality.
Innovation Solution
A color control loop that generates a correction to the PWM value of the LED responsive to the sensed LED output prior to a change in the target value, allowing for at least one cycle to complete between target value changes, enabling rapid adjustment of color balance and luminance to match changing video signal requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the color control loop completes at least one cycle between target value changes, then the accuracy of color balance and luminance adjustment is improved, but the response time to changing video signal requirements increases
Solution Approach 1:
The control loop generates corrections in advance based on predicted LED output changes, allowing the system to prepare adjustment values before the actual LED state changes. This preliminary computation enables faster response while maintaining accuracy by having correction values ready to be applied immediately when target values change.
Solution Approach 2:
The system continuously monitors actual LED output and compares it with target values, generating correction signals that are applied to PWM duty cycles. This feedback mechanism ensures accurate color balance and luminance adjustment by constantly refining the output based on real measurements, resolving the contradiction between speed and precision.
2Measurement precision
If PWM frequency is increased to improve luminance control precision, then the luminance control precision is improved, but the complexity of the control system increases
Solution Approach 1:
The system adjusts PWM duty cycle values based on color and luminance corrections derived from feedback measurements. By modifying the duty cycle parameters dynamically rather than increasing fundamental PWM frequency, the system achieves precise luminance control without proportionally increasing control system complexity.
Solution Approach 2:
The patent replaces complex high-frequency PWM control mechanisms with a simplified feedback-based correction system. Instead of relying solely on high-frequency switching, the system uses intelligent control algorithms that calculate and apply corrections to duty cycles, reducing the mechanical complexity of the control system while maintaining precision.
3Illumination intensity
If the backlight is illuminated for a longer duration, then the illumination intensity is improved, but the motion blur increases
Solution Approach 1:
The scanning backlight illuminates different zones of the display in sequential periods, with each zone receiving light for a specific duration synchronized with the video signal refresh rate. This periodic illumination pattern ensures sufficient light intensity for each zone while minimizing overall illumination time to reduce motion blur effects.
Solution Approach 2:
The system dynamically adjusts the illumination duration and timing of the backlight based on the current video signal and detected scene conditions. By making the illumination parameters adaptive rather than fixed, the system optimizes the balance between providing sufficient light intensity and limiting exposure time to minimize motion blur.
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 rapid and accurate adjustment of color balance and luminance, improving contrast and reducing motion blur by ensuring that the LED output matches the desired target values within a single cycle, thereby enhancing the overall image quality and responsiveness to changing scene conditions.
Implementation Method 1
Light emitting diodes (LEDs) and in particular high intensity and medium intensity LED strings are rapidly coming into wide use for lighting applications
Implementation Method 2
the white LEDs typically comprising a blue LED with a phosphor which absorbs the blue light emitted by the LED and emits a white light
Data Source
AI summary
A method of controlling the output of a luminaire by receiving a first target signal associated with a first frame; generating a first light output control signal for an on time portion of the first frame, the light output control signal responsive to the received first target signal; sampling a light output during the on time portion of the first frame, the light output being responsive to the first light output control signal; receiving a second target signal associated with a second frame, the second frame following the first frame; comparing the received second target signal with the sampled light output of the on time portion of the first frame; and generating an error signal responsive to the comparing.