Liquid Crystal Display Local Dimming via Average Picture Level
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Solution Overview
Problem
Liquid crystal displays using LED backlight units struggle to partially emphasize image brightness due to dimming signal generation based on a fixed dimming curve, leading to reduced power consumption and potential side effects like screen darkening or flashing, especially with abrupt or slow gray level variations in input data.
Innovation Solution
A liquid crystal display system that generates dimming signals based on the average picture level (APL) of input video data, using a timing controller with an APL detector and lookup tables to provide pulse width modulation (PWM) control signals to LED arrays partitioned across the display, allowing for dynamic adjustment of light transmittance to match image content.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a fixed dimming curve is used to generate dimming signals for LED backlight units, then the control system is simple, but the display cannot partially emphasize image brightness and may cause screen darkening or flashing
Solution Approach 1:
The patent divides the LED backlight unit into multiple independently controllable LED arrays (first LED array and second LED array). Each array can be controlled by separate dimming signals, allowing different brightness levels in different regions. This segmentation enables partial emphasis of image brightness without requiring complex overall dimming curves, resolving the contradiction between control simplicity and display quality.
Solution Approach 2:
The patent applies different dimming signals to different LED arrays based on local image characteristics. The timing controller generates first and second dimming signals with different duty ratios according to the average picture level (APL) of different regions, enabling local brightness adjustment. This local quality approach maintains simple overall control while improving display quality through region-specific optimization.
2Use of energy by moving object
If LED backlight units are used instead of fluorescent lamps, then power consumption is reduced and brightness is improved, but the ability to dynamically adjust brightness based on image content is limited
Solution Approach 1:
The patent implements dynamic brightness adjustment by having the timing controller continuously monitor the APL of input video signals and dynamically adjust the duty ratios of dimming signals sent to different LED arrays. This dynamic adaptation maintains low power consumption through LED efficiency while adding versatility through real-time content-based brightness control, resolving the contradiction between energy efficiency and adaptability.
Solution Approach 2:
The patent introduces feedback mechanisms where the timing controller analyzes the APL of video content and uses this information to generate appropriate dimming signals. The system continuously adapts LED backlight brightness based on feedback from image content analysis, enabling dynamic brightness adjustment that maintains low power consumption while improving adaptability to different display scenarios.
3Device complexity
If a single dimming signal is applied to all LED arrays, then the control structure is simple, but gray scale-based dimming range is limited and image representation is poor
Solution Approach 1:
The patent segments the backlight control into multiple independent LED arrays, each receiving tailored dimming signals. This segmentation enables precise gray scale control for different regions without requiring complex overall control structures, as each array can be independently optimized based on local image requirements.
Solution Approach 2:
The patent changes the duty ratio parameter of PWM dimming signals differently for different LED arrays based on their respective APL values. This parameter adjustment enables precise gray scale control across different regions, improving image representation while maintaining relatively simple control structures through systematic parameter variation.
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 reduces power consumption and improves display quality by optimizing dimming based on real-time APL, minimizing side effects like screen darkening or flashing, and enhancing the gray scale-based dimming range for better image representation.
Implementation Method 1
a liquid crystal panel having a plurality of liquid crystal cells formed respectively in a plurality of pixel areas
Implementation Method 2
a light emitting diode (LED) backlight unit for partitioning the liquid crystal panel into a plurality of areas and supplying appropriate pulse width modulation (PWM) control signals
Data Source
AI summary
Disclosed herein is a liquid crystal display capable of reducing a side effect during local LED dimming to reduce power consumption and improve display quality. The liquid crystal display includes a liquid crystal panel having a plurality of liquid crystal cells formed respectively in a plurality of pixel areas defined by intersections of a plurality of gate lines and a plurality of data lines, a data driver for supplying data voltages to the data lines, a gate driver for supplying scan signals to the gate lines, a timing controller for controlling the data driver and gate driver and outputting a plurality of dimming signals based on an average picture level (APL) detected based on video data supplied to the liquid crystal panel, and a light emitting diode (LED) backlight unit for partitioning the liquid crystal panel into a plurality of areas and supplying appropriate pulse width modulation (PWM) control signals based on the dimming signals to a plurality of LED arrays installed to correspond respectively to the partitioned areas, to supply light to the liquid crystal panel.