LCD Panel Counter-Voltage Compensation for Luminance Uniformity
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Solution Overview
Problem
Existing liquid-crystal display apparatuses suffer from luminance non-uniformity and flicker due to varying pull-in voltages across the panel, causing the optimum counter voltage to deviate and leading to uneven brightness, especially at the edges and center of the screen.
Innovation Solution
A liquid-crystal display apparatus with a matrix arrangement of pixels, where each row receives a scan signal applied to a control electrode, and a signal is raised on the signal line when the scan signal falls, canceling out the pull-in voltage effects by matching the voltage push-down and push-up across the panel.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a scan signal is applied to the gate of TFT in conventional liquid-crystal display apparatus, then the data signal can be written in the pixel electrode, but a pull-in voltage occurs due to parasitic capacitance between gate and drain, causing the pixel electrode voltage to drop below the data signal voltage
Solution Approach 1:
The patent applies a preliminary counter-voltage to the counter electrode before the scan signal falls, which counteracts the pull-in voltage effect. By anticipating the voltage drop caused by parasitic capacitance discharge, the system pre-applies an opposing voltage to maintain the pixel electrode voltage at the correct level, preventing display defects like white spots or lines.
2Speed
If the scan signal waveform deforms with distance from the driving end due to distributed constant line characteristics, then signal propagation occurs across the panel, but the pull-in voltage magnitude varies with position, causing luminance non-uniformity
Solution Approach 1:
The patent implements position-dependent counter-voltage compensation by dividing the display panel into multiple regions along the scan-signal line direction. Each region receives a specifically tailored counter-voltage waveform that accounts for the local signal deformation characteristics at that position, ensuring uniform luminance across the entire panel despite varying signal propagation effects.
Solution Approach 2:
The patent changes the counter-voltage parameters (amplitude, timing, duration) based on the position along the scan-signal line. By adjusting these parameters locally for different panel regions, the system compensates for position-dependent signal deformation and maintains consistent display quality across the entire screen.
3Speed
If the scan signal falls rapidly at the panel edge, then the TFT turns off quickly, but the pull-in voltage causes significant voltage drop in the pixel electrode, whereas at the panel center the slow fall causes delayed TFT turn-off and recharging effects
Solution Approach 1:
The patent applies the counter-voltage to the counter electrode in advance before the scan signal falls, regardless of position. This preliminary action prepares the pixel electrode voltage to resist the impending pull-in voltage effect, ensuring consistent voltage maintenance at both panel edges and center where TFT switching behavior differs.
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 configuration maintains a consistent counter voltage across the panel, preventing luminance non-uniformity and flicker, ensuring uniform brightness and reducing the occurrence of burn-in from DC components.
Implementation Method 1
it is known that when the driving voltage for the gate rises, a feed-through voltage (so-called pull-in voltage) occurs due to the influence of the parasitic capacitance between the gate and the drain of the TFT
Data Source
AI summary
A liquid-crystal display apparatus and a method for driving liquid-crystal display apparatus are provided. Pixels arrayed in a form of a matrix are each defined so as to include an electrode pair consisting of a pixel electrode and a counter electrode facing one another via a liquid-crystal layer, and a scan signal is applied, from a scan-signal line for each line, to a control electrode of a TFT for applying a data signal to the pixel electrode included in the pixel. A signal to be raised when the scan signal for each line falls is applied to a signal line arranged between a pixel in each line and a pixel adjacent to the pixel at one side in the line direction.