KSF LED Backlight Dimming for Red Afterimage and Gray Levels
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Solution Overview
Problem
The use of KSF phosphor in LED backlights for liquid crystal displays leads to red afterimages due to excitation of red luminance during the duty-off interval of the PWM signal, and increasing the driving frequency to mitigate this issue results in reduced gray level expression and image resolution.
Innovation Solution
A display device with a liquid crystal panel and a backlight system that includes KSF phosphor LEDs, where a controller determines the duty of the light source driving signal based on global and local dimming values, adjusting the constant current to maintain gray level expression even with increased driving frequency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the driving frequency of the PWM signal is increased to prevent red afterimages, then the red afterimage problem is improved, but the gray level expression power is reduced and image resolution is reduced
Solution Approach 1:
The backlight is divided into multiple independently controllable backlight blocks, each with its own PWM duty cycle control. This segmentation allows different regions to have different dimming values, enabling the system to maintain sufficient gray level expression in regions where PWM frequency is increased while avoiding red afterimages only where necessary.
Solution Approach 2:
Different regions of the backlight are assigned different quality characteristics through local dimming control. Some regions use higher PWM frequencies to eliminate red afterimages, while others maintain lower frequencies to preserve gray level expression, with each region optimized independently based on its specific requirements.
2Object-affected harmful factors
If the driving frequency of the PWM signal is increased to prevent red afterimages, then the red afterimage problem is improved, but the image resolution is reduced
Solution Approach 1:
The backlight is divided into multiple independently controllable backlight blocks, each with its own PWM duty cycle control. This segmentation allows different regions to have different dimming values, enabling the system to maintain sufficient gray level expression in regions where PWM frequency is increased while avoiding red afterimages only where necessary.
Solution Approach 2:
Different regions of the backlight are assigned different quality characteristics through local dimming control. Some regions use higher PWM frequencies to eliminate red afterimages, while others maintain lower frequencies to preserve gray level expression, with each region optimized independently based on its specific requirements.
3Measurement precision
If the duty of the light source driving signal is determined only with the local dimming value, then the gray level expression is maintained, but the overall brightness control is reduced
Solution Approach 1:
The patent merges global dimming control and local dimming control into a unified system. The global dimming value provides overall brightness control for the entire backlight, while local dimming values provide region-specific adjustments. Both control mechanisms work together to determine the final PWM duty cycle, maintaining both overall brightness control and gray level expression.
Solution Approach 2:
The backlight control system is designed with multi-functionality, serving both global brightness adjustment and local gray level expression needs. The same PWM control mechanism handles both global and local dimming requirements, making the system versatile in meeting different display requirements simultaneously.
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
Prevents red afterimages and maintains gray level expression by optimizing the light source driving signal duty, ensuring improved image quality without reducing resolution.
Implementation Method 1
KSF phosphor is a phosphor that emits Deep Red light and is used for excellent color reproduction
Implementation Method 2
each LED is formed of KSF (Kalium Silicon Floride) phosphor
Data Source
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AI summary
A display device comprises a liquid crystal display panel; a backlight configured to output a light to the liquid crystal display panel, wherein the backlight includes a plurality of backlight blocks and a light source driving circuit configured to generate a light source driving signal for controlling a light output of the backlight block, each backlight block has one or more LEDs (Light Emitting Diodes); and each LED is formed of KSF (Kalium Silicon Floride) phosphor; and a controller configured to: obtain a global dimming value and a local dimming value (S1401), determine a duty of the light source driving signal as the local dimming value (S1405) if the global dimming value is less than a certain value (S1403), and reduce a constant current applied to the backlight block based on the global dimming value (S1407).