Scanning Backlight PWM Control for LCD Flicker and Motion Blur
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Solution Overview
Problem
Existing scanning backlight driving technologies for liquid crystal displays (LCDs) are not effective for 60 Hz models, causing perceived flicker and motion blur, and fail to maintain screen luminance due to turn-off times during frame periods.
Innovation Solution
A liquid crystal display system that uses a scanning backlight controller and light source driver to calculate and adjust the turn-on duty ratio of a PWM signal, synchronizing its frequency with 60 Hz, and varying the amplitude to minimize flicker and maintain luminance, by comparing the duty ratio with a critical value and adjusting the driving current and timing of light sources.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If scanning backlight driving technology is applied to 60 Hz LCD models, then motion blur is reduced, but flicker is perceived by users
Solution Approach 1:
The patent implements periodic backlight scanning synchronized with the 60 Hz frame rate, dividing each frame into multiple scanning periods where light sources are sequentially activated. This periodic action reduces motion blur by creating impulsive drive effects while maintaining synchronization to eliminate flicker perception.
Solution Approach 2:
The patent dynamically adjusts the turn-on duty ratio of the PWM signal based on the scanning position and frame timing. By making the backlight drive dynamic rather than static, the system can optimize motion blur reduction while maintaining perceived luminance and eliminating flicker at 60 Hz.
2Speed
If light sources are turned off for predetermined time in each frame period, then motion blur is reduced, but screen luminance decreases
Solution Approach 1:
The patent changes the duty ratio parameter of the PWM signal controlling the light sources. By adjusting the turn-on duty ratio to optimize values during scanning periods, the system achieves motion blur reduction while compensating for luminance loss through parameter optimization rather than fixed timing.
Solution Approach 2:
The patent ensures continuous useful action by overlapping scanning periods across frames and maintaining appropriate duty ratios. This continuity ensures that while individual light sources are turned off temporarily for motion blur reduction, the overall backlight illumination remains sufficient to maintain screen luminance.
3Illumination intensity
If turn-off time of light sources is controlled based on screen brightness, then luminance is maintained, but motion blur reduction effect is reduced
Solution Approach 1:
The patent segments the backlight control into distinct scanning periods within each frame, where different light sources are activated sequentially. This segmentation allows motion blur reduction through selective timing while the aggregate effect across all segments maintains overall luminance, resolving the contradiction between luminance maintenance and motion blur reduction.
Data Source
AI summary
A liquid crystal display includes a scanning backlight controller, that calculates a turn-on duty ratio of a pulse width modulation (PWM) signal for controlling turn-on and turn-off operations of light sources, and a light source driver, that synchronizes a frequency of the PWM signal with a frame frequency or synchronizes the frequency of the PWM signal with the frame frequency, changes the calculated turn-on duty ratio of the PWM signal to a maximum value, and adjusts an amplitude of the PWM signal based on a changed degree of the turn-on duty ratio of the PWM signal, based on the result of a comparison between the turn-on duty ratio of the PWM signal and a previously determined critical value, and then sequentially drive the light sources along a data scanning direction of the liquid crystal display panel.