Light Source Control Apparatus for Phosphorescent LED Backlight Afterglow Reduction
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Solution Overview
Problem
Liquid crystal display devices using white LEDs that emit phosphorescence face image quality degradation due to afterglow issues, particularly when high-speed objects are displayed, as phosphorescence remains visible after the object has moved, affecting brightness control and dynamic characteristics.
Innovation Solution
A light source control apparatus that generates drive pulses with constant amplitude and pulse width for dark and bright portions, respectively, based on lighting values, to stabilize brightness and reduce afterglow effects by employing area control strategies for the backlight, ensuring optimal PWM and current control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If PWM control with decreased pulse width is used to decrease brightness, then brightness control precision is improved, but afterglow of phosphorescence occurs causing image quality degradation
Solution Approach 1:
The patent dynamically switches between two drive modes (PWM control and current control) based on the brightness level. For dark portions requiring precise brightness control, PWM control is used. For bright portions where phosphorescence afterglow becomes problematic, current control with fixed pulse width is used. This dynamic adaptation resolves the contradiction by selecting the appropriate control method for each operating condition.
Solution Approach 2:
The patent changes the control parameter from PWM duty cycle to drive current when transitioning from dark to bright portions. By switching the controlled parameter based on brightness level, the system achieves precise brightness control in dark areas while avoiding phosphorescence afterglow in bright areas, thus resolving the technical contradiction.
2Stability of the object's composition
If current control is used in dark portions, then brightness stability is improved, but afterglow occurs in bright portions degrading image quality
Solution Approach 1:
The patent applies different control strategies to different brightness regions: current control is applied locally to dark portions where brightness stability is needed, while PWM control is applied to bright portions where phosphorescence afterglow must be avoided. This localized application of different control methods resolves the contradiction between brightness stability and afterglow prevention.
Solution Approach 2:
The patent segments the brightness range into dark portions and bright portions, applying different control methods to each segment. This segmentation allows the system to optimize for brightness stability in dark areas while preventing afterglow in bright areas, resolving the technical contradiction.
3Object-affected harmful factors
If PWM control is used in bright portions, then afterglow is reduced, but brightness control precision deteriorates
Solution Approach 1:
The patent dynamically selects the control method based on the brightness level. In bright portions, PWM control is used to minimize phosphorescence afterglow. In dark portions, current control is used to achieve precise brightness control. This dynamic selection resolves the contradiction by using the appropriate control method for each brightness level.
4Illumination intensity
If the pulse width is decreased to decrease brightness, then brightness control is improved, but PWM control stability deteriorates due to timing relationship issues
Solution Approach 1:
The patent changes the control parameter from PWM duty cycle to drive current when operating in dark portions. By using current control instead of PWM control for dark portions, the system achieves precise brightness control without the timing-related stability issues that plague narrow pulse width PWM control, thus resolving the technical contradiction.
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 minimizes afterglow effects and maintains good dynamic characteristics by adjusting PWM and current control according to lighting value ranges, enhancing image quality and reducing hold blur in liquid crystal display devices.
Implementation Method 1
Light-emitting diodes (LEDs) may be used for the light sources of liquid crystal display devices... A white LED prepared by combining fluorescent elements emitting green light and red light with blue light having a short wavelength as an excitation light source is used. A white LED may use a phosphorescent element which emits phosphorescence as well as fluorescence to realize a wide gamut. Fluorescence disappears at once (in approximately one billionth of a second to one hundred-thousandth of a second). However, phosphorescence disappears in approximately one thousandth of a second to several seconds.
Data Source
AI summary
According to one embodiment, a light source control apparatus controls a light source emitting phosphorescence. The light source control apparatus includes a driver configured to supply a drive pulse to the light source. The driver is configured to generate a first drive pulse comprising constant amplitude and a pulse width based at least in part on the lighting value and a second drive pulse comprising a constant pulse width and amplitude based at least in part on the lighting value. The driver is configured to supply the first drive pulse or the second drive pulse to the light source in accordance with the lighting value.