Liquid Crystal Display Discharge Circuit for Residual Pattern Removal
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Solution Overview
Problem
Liquid crystal display (LCD) devices experience prolonged discharge times due to leakage currents through thin film transistors (TFTs) when power is removed, leading to residual patterns that take time to disappear.
Innovation Solution
A power supply unit outputs a constant gate-on voltage to TFTs, using a discharge unit with diodes, resistors, and transistors to rapidly discharge gradation display voltages from liquid crystal capacitors when power is removed, reducing discharge time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If ground voltage is applied to the gate of the TFT when power is removed, then the liquid crystal capacitor discharges through leakage current, but the discharge time becomes prolonged
Solution Approach 1:
Instead of applying ground voltage to discharge the capacitor through leakage current, the patent applies gate-on voltage to actively turn on the TFT and create a controlled discharge path. This inverts the conventional approach from passive leakage-based discharge to active voltage-based discharge, significantly reducing discharge time.
Solution Approach 2:
The patent changes the voltage parameter applied to the TFT gate from ground voltage (0V) to gate-on voltage (e.g., +20V). This parameter change transforms the TFT from a leakage discharge mode to an active conduction mode, enabling rapid controlled discharge of the liquid crystal capacitor through the data line.
2Device complexity
If leakage current through TFT channel is used for discharge, then simple structure is maintained, but discharge speed is slow
Solution Approach 1:
The patent prepares the discharge path in advance by storing the gate-on voltage in the discharge unit capacitor during normal operation. When power is removed, this pre-stored voltage is immediately available to turn on the TFT and initiate rapid discharge, eliminating the need for complex real-time voltage generation circuits.
Solution Approach 2:
The discharge unit acts as an intermediary component that bridges the power supply unit and the liquid crystal panel. It stores energy in its capacitor and provides the gate-on voltage to the TFT, enabling controlled discharge without requiring direct modification of the main display circuitry.
3Reliability
If threshold voltage distribution or increase occurs due to long driving time, then TFT reliability decreases, but discharge time becomes unpredictable
Solution Approach 1:
The patent applies gate-on voltage to the TFT gate, which provides a feedback mechanism that compensates for threshold voltage variations. The gate-on voltage ensures the TFT conducts sufficiently to enable discharge, counteracting the effect of increased threshold voltage due to aging or distribution variations.
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 significantly reduces discharge time by actively discharging gradation display voltages through TFTs, ensuring patterns disappear quickly and maintaining desirable discharge quality characteristics.
Implementation Method 1
a discharge unit which charges a charging voltage when a supply voltage at the first level is input to the discharge unit and outputs the charged charging voltage as a discharge signal when a supply voltage at the second level is input to the discharge unit
Implementation Method 2
the data signal voltage applied to the liquid crystal capacitor is discharged by a leakage current through a channel of the TFT
Data Source
AI summary
A liquid crystal display device includes: a power supply unit which outputs a supply voltage at a first level when an outside power is supplied and outputs the supply voltage at a second level when the outside power is removed; a discharge unit which outputs a discharge signal when the supply voltage at the second level is input; and a liquid crystal panel including a gate discharge line, a plurality of gate lines connected to the gate discharge line, a plurality of thin film transistors connected to the plurality of gate lines, and a plurality of liquid crystal capacitors connected to the thin film transistors and which charges to a gradation display voltage. The thin film transistor is turned on to discharge the gradation display voltage charged in the plurality of liquid crystal capacitors when the discharge signal is provided to the gate discharge line.