FFS LCD DC Bias Correction for Image Sticking
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Solution Overview
Problem
Liquid crystal display devices in FFS mode often experience image sticking, where a gray picture remains as a persistent image after displaying a monochrome checkered pattern, due to fluctuations in pixel electrode voltage and DC offset, leading to inconsistent brightness and gradation display.
Innovation Solution
A liquid crystal display device with a correcting circuit that adjusts pixel voltages by adding a predetermined DC bias based on gradation to cancel out DC shift and brightness deviation, ensuring consistent brightness across different gradations and reducing image sticking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If FFS mode is used to achieve large aperture ratio and high brightness, then aperture ratio and brightness are improved, but image sticking phenomenon occurs due to DC offset and voltage fluctuations
Solution Approach 1:
The patent applies parameter changes by introducing a DC bias voltage to the pixel electrode that varies according to the displayed gradation level. This modifies the voltage parameters dynamically to compensate for the DC offset caused by image sticking, thereby maintaining reliable display performance while preserving the high brightness characteristics of FFS mode.
Solution Approach 2:
The patent implements a feedback mechanism where the display control circuit monitors the displayed image content and adjusts the pixel electrode voltage by adding appropriate DC bias based on the gradation being displayed. This feedback loop continuously compensates for image sticking effects, ensuring that persistent images do not occur even when operating in high-brightness FFS mode.
2Reliability
If DC bias is added to pixel electrode to correct image sticking, then image sticking is reduced, but device complexity increases due to correcting circuit
Solution Approach 1:
The display control circuit is designed to perform multiple functions: it controls the normal display operation, manages the timing of voltage application, and simultaneously executes the image sticking correction by adding DC bias based on gradation. This multi-functionality reduces the need for separate dedicated correction hardware, thereby limiting the increase in device complexity while maintaining improved reliability.
3Illumination intensity
If pixel voltage is adjusted to stabilize brightness, then brightness consistency is improved, but manufacturing precision requirements increase
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing the appropriate DC bias values for each gradation level in the display control circuit. During operation, the circuit simply retrieves and applies the predetermined bias voltage corresponding to the current gradation, rather than requiring real-time calculation or high-precision analog adjustments. This approach achieves stable brightness consistency while reducing the actual manufacturing precision requirements during production.
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
The solution effectively reduces image sticking by stabilizing brightness and gradation display, improving the overall quality of the liquid crystal display device by minimizing fluctuations in brightness-VCOM characteristics curves.
Implementation Method 1
the direction of alignment of the liquid crystal molecule contained in the liquid crystal layer is controlled by electrical field impressed between the counter electrode and the pixel electrodes
Implementation Method 2
a liquid crystal layer is held between a counter electrode formed on an upper side substrate and pixel electrodes formed on a lower side substrate, and the direction of alignment of the liquid crystal molecule contained in the liquid crystal layer is controlled
Data Source
AI summary
A liquid crystal display device includes an array substrate, a counter substrate and a liquid crystal layer held between the array substrate and the counter substrate. A display portion having a plurality of pixels arranged in a matrix is formed of the substrates and the liquid crystal layer. Each of the pixels includes a pixel electrode and a counter electrode arranged opposing to the pixel electrode. A driving portion is formed on the array substrate to supply a pixel voltage to the pixel electrode. A correcting circuit is formed on the array substrate to correct the voltage supplied to the pixel electrode by adding a predetermined DC voltage to the voltage supplied to the pixel electrode corresponding to gradations to be displayed in the pixel.