LCD Backlight PWM Control for KSF Red Afterimage Suppression
Find Innovative SolutionsGenerate Solutions
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 duty-off intervals of the PWM signal, and increasing the driving frequency to mitigate this issue reduces gray level expression and image resolution.
Innovation Solution
A display device with a liquid crystal panel and a backlight system that includes multiple backlight blocks and a light source driving circuit, where a controller determines the duty of the light source driving signal based on global and local dimming values to maintain gray level expression even with increased PWM 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 and image resolution are reduced
Solution Approach 1:
The patent applies dynamics by making the PWM driving frequency variable rather than fixed. The controller dynamically adjusts the PWM frequency based on the brightness level of the displayed image: using high frequency (e.g., 480Hz) when brightness is low to prevent red afterimages, and switching to low frequency (e.g., 60Hz) when brightness is high to maintain adequate gray level expression. This dynamic frequency adjustment resolves the contradiction by adapting the driving parameters to actual display conditions.
Solution Approach 2:
The patent changes the PWM driving frequency parameter based on brightness conditions. By monitoring the brightness level and adjusting the frequency parameter accordingly, the system optimizes both afterimage prevention and gray level expression. Additionally, the patent adjusts the duty cycle parameter to compensate for frequency changes, ensuring that the combination of frequency and duty cycle maintains appropriate gray level resolution across different operating conditions.
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 patent applies dynamics by making the PWM driving frequency variable rather than fixed. The controller dynamically adjusts the PWM frequency based on the brightness level of the displayed image: using high frequency (e.g., 480Hz) when brightness is low to prevent red afterimages, and switching to low frequency (e.g., 60Hz) when brightness is high to maintain adequate gray level expression. This dynamic frequency adjustment resolves the contradiction by adapting the driving parameters to actual display conditions.
Solution Approach 2:
The patent changes the PWM driving frequency parameter based on brightness conditions. By monitoring the brightness level and adjusting the frequency parameter accordingly, the system optimizes both afterimage prevention and gray level expression. Additionally, the patent adjusts the duty cycle parameter to compensate for frequency changes, ensuring that the combination of frequency and duty cycle maintains appropriate gray level resolution across different operating conditions.
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 while maintaining gray level expression by adjusting the duty of the light source driving signal, 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. Due to its own characteristics, the KSF phosphor generates a phenomenon in which red luminance is excited compared to green and blue in the duty-off interval of the PWM signal.
Data Source
AI summary
According to an embodiment of the present disclosure, a display device may comprise 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 (Potassium fluorosilicate) phosphor; and a controller configured to: obtain a global dimming value and a local dimming value, determine a duty of the light source driving signal as the local dimming value if the global dimming value is less than a certain value, and reduce a constant current applied to the backlight block based on the global dimming value.