Liquid Crystal Display Kickback Prevention via Floating Common Electrode
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Solution Overview
Problem
In liquid crystal display devices, potential variation (kickback) induced by parasitic capacitance when a transistor changes from an on state to an off state can cause a DC voltage to be applied across a pixel, leading to image sticking and flickering, especially in devices with good off-state characteristics that suppress self-discharge.
Innovation Solution
A liquid crystal display device configuration that includes a data signal line, a scan signal line, a pixel electrode, and a common electrode, where the transistor is turned on during the power-off sequence by changing the electric potential of the scan signal line, and the common electrode is placed in an electrically floating state at a specific timing, allowing the pixel electrode to discharge electric charge and preventing DC voltage application.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the transistor is turned on during power-off sequence to discharge electric charge at the pixel electrode, then image sticking and flickering are prevented, but potential variation (kickback) is induced by parasitic capacitance when the transistor changes from on state to off state, causing DC voltage to be applied across the pixel
Solution Approach 1:
A capacitor is introduced as an intermediary component connected between the pixel electrode and the common electrode. This capacitor acts as a mediator that provides an alternative discharge path for electric charge, thereby preventing kickback-induced DC voltage from appearing across the pixel when the transistor switches from on to off state during power-off sequence.
Solution Approach 2:
The capacitor is pre-charged to a specific potential before the transistor switches off. This preliminary charging ensures that when the transistor turns off and kickback occurs, the capacitor can immediately provide a discharge path, preventing DC voltage from being applied across the pixel electrode and common electrode.
2Duration of action of moving object
If the transistor has good off-state characteristics to suppress self-discharge, then charge retention is improved, but DC voltage is applied across the pixel for an extended period of time
Solution Approach 1:
The capacitor serves as a mediator that becomes active specifically during the power-off sequence. It provides a controlled discharge path that operates independently of the transistor's off-state characteristics, ensuring that even when the transistor has excellent charge retention properties, the capacitor can still prevent prolonged DC voltage application by offering an alternative discharge mechanism.
3Loss of energy
If the transistor is turned on during power-off sequence, then electric charge is discharged from the pixel electrode, but image sticking and flickering occur due to DC voltage application
Solution Approach 1:
The capacitor acts as an intermediary that enables safe charge discharge. By providing an alternative discharge path through the capacitor, the harmful effects of direct discharge through the transistor (kickback and DC voltage application) are avoided, while still achieving the beneficial effect of charge removal from the pixel electrode.
Solution Approach 2:
The harmful DC voltage component is extracted from the discharge path by introducing the capacitor as a separate parallel path. This allows the useful charge discharge function to continue while the harmful DC voltage application is removed from the system.
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 effectively prevents the application of DC voltage across the pixel even when kickback occurs, enhancing the reliability of the liquid crystal display device by ensuring no prolonged DC voltage is applied.
Implementation Method 1
potential variation (kickback) is induced by surrounding parasitic capacitance when the transistor is changed from an on state to an off state
Implementation Method 2
Liquid crystal display device includes a liquid crystal panel
Data Source
AI summary
A liquid crystal display device includes: a data signal line; a scan signal line; a pixel electrode; a transistor connected to (i) the data signal line, (ii) the scan signal line, and (iii) the pixel electrode; and a common electrode, the liquid crystal display device being configured to turn on the transistor during a power-off sequence by causing a change in an electric potential of the scan signal line, the electric potential of the scan signal line reaching a first electric potential at a first timing after the change is initiated, and the common electrode being in an electrically floating state at a second timing which comes after the first timing. This, in a case where the transistor is turned on in preparation for an operation to turn off a power source of the liquid crystal display device, makes it unlikely for a DC voltage to be applied across a pixel even if potential variation (kickback) occurs at the pixel electrode in reaction to a change in status of the transistor from an on state to an off state.