Liquid Crystal Display Polarity Control for DC Image Sticking
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Solution Overview
Problem
Active matrix liquid crystal displays suffer from direct current (DC) image sticking, flicker, and stains due to prolonged application of DC voltage, which degrade display quality and alignment characteristics, and existing solutions either require long development times or reduce drive characteristics.
Innovation Solution
A liquid crystal display system with a data drive circuit that inverts the polarity of the data voltage and a timing controller that extends the logic inverting period of the polarity control signal during specific frame periods, time-dividing liquid crystal cells to charge them with alternating polarities and dispersing accumulated voltage across multiple frames, thereby preventing DC image sticking and flicker.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Extent of automation
If data voltage is supplied in an interlaced manner to liquid crystal cells, then the liquid crystal display can operate with active matrix control, but DC image sticking occurs due to dominant positive polarity voltage accumulation
Solution Approach 1:
The patent applies periodic polarity inversion to the data voltage supplied to liquid crystal cells. Instead of maintaining a dominant positive polarity in interlaced mode, the system periodically inverts the polarity between frames, ensuring that odd and even horizontal lines receive alternating polarities. This periodic action prevents the accumulation of DC offset and eliminates image sticking while preserving active matrix control capabilities.
2Reliability
If polarity is inverted every frame period, then DC offset components are reduced, but image sticking still occurs when the same image is displayed for extended periods
Solution Approach 1:
The patent segments the display into different scanning modes (interlaced and progressive) and applies different polarity inversion strategies to each. In interlaced mode, polarity inversion is extended to cover multiple frames (e.g., 4 frames) rather than just one frame, creating a segmented approach where the inversion period adapts to the scanning mode. This segmentation allows the system to maintain DC offset reduction while preventing image sticking through extended polarity alternation.
3Ease of operation
If the liquid crystal display uses conventional polarity inversion, then basic display function is maintained, but stains appear due to ion accumulation from prolonged DC voltage application
Solution Approach 1:
The patent implements dynamic polarity control that adapts to different display conditions and scanning modes. The system dynamically adjusts the polarity inversion period based on whether interlaced or progressive scanning is used, and modifies the inversion pattern to ensure that no region receives prolonged DC voltage of the same polarity. This dynamic approach maintains basic display functionality while preventing ion accumulation and stain formation through adaptive polarity management.
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 reduces DC image sticking and flicker, improving display quality by ensuring alternating polarities are maintained across multiple frames, thus preventing the accumulation of ions and reducing stain formation.
Implementation Method 1
a liquid crystal display and a method of driving the same capable of preventing DC image sticking, flicker, and stains by extending a logic inverting period of a polarity control signal during specific frame periods
Implementation Method 2
Active matrix type liquid crystal displays display a moving picture using a thin film transistor (TFT) as a switching element
Data Source
AI summary
A liquid crystal display and a method for driving the same are disclosed. The liquid crystal display includes a timing controller generating a polarity control signal. A logic inverting period of the polarity control signal during frame periods ranging from an Nth frame period among M frame periods to 2 to 4 frame periods following the Nth frame period is longer than a logic inverting period of the polarity control signal in the other frame periods, where N is an integer equal to or larger than 4 and M is larger than N. The liquid crystal cells in one frame period of the M frame periods are charged to the data voltage whose a polarity is opposite to a polarity of the data voltage in a previous frame period of one frame period.