LCD Discharging Unit for Afterimage Prevention
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Solution Overview
Problem
Liquid crystal display devices experience afterimages when the power source is turned off due to slow discharge of electric charges from pixel cells, causing temporary image retention on the screen.
Innovation Solution
A liquid crystal display device with a discharging unit that controls the output of a gate driver to simultaneously drive all gate lines or drive them in a phased manner when the power source is turned off, using clock pulses with phase differences and an RC time constant-based delay to rapidly discharge voltage from pixels, preventing afterimages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the power source is turned off normally, then energy consumption is reduced, but afterimages occur on the screen due to slow discharge of electric charges from pixels
Solution Approach 1:
The patent applies preliminary action by initiating a discharge process before the pixel completely loses its stored charge. When power is turned off, the gate driver continues to output gate voltages for a predetermined period, actively discharging the pixel cells through the liquid crystal capacitors and auxiliary capacitors. This pre-discharge action prevents afterimages from forming in the first place, rather than waiting for natural discharge to occur.
2Device complexity
If gate lines are driven sequentially during normal operation, then pixel addressing is simplified, but voltage discharge from pixels is slow when power is turned off
Solution Approach 1:
The patent applies periodic action by using alternating high and low gate voltages to drive the gate lines during the discharge period. The gate driver outputs gate voltages that switch between high and low states in a periodic manner, creating oscillating electric fields that accelerate the discharge of charge from the pixel cells. This periodic voltage application forces the liquid crystal and auxiliary capacitors to repeatedly charge and discharge, significantly speeding up the overall discharge process compared to a single static voltage level.
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 prevents afterimages by rapidly discharging voltage from all pixels when the power source is turned off, ensuring a clear screen upon power-off.
Implementation Method 1
using clock pulses with phase differences and an RC time constant-based delay
Implementation Method 2
The light transmittance of liquid crystal layer is controlled based on an intensity of electric field generated between the pixel electrode and the common electrode
Data Source
AI summary
A liquid crystal display device and driving method thereof is disclosed, which is capable of removing afterimages from a screen when a power source is turned-off, the liquid crystal display device comprising a liquid crystal panel including a plurality of pixels defined by a plurality of gate and data lines crossing each other; a gate driver for driving the gate lines; a data driver for charging the pixels with analog video signals through the data lines; and a discharging unit for discharging voltage from the pixels by controlling the output of gate driver to make all the gate lines being divisionally driven or to make all the gate lines being driven at the same time when a power source is turned-off.