JP3737006B2 - Method for reducing residual image on liquid crystal display - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for controlling a liquid crystal display, and more particularly to a method for reducing a residual image on a discharge liquid crystal display by shortening a discharge time when the liquid crystal display is turned off.
[0002]
[Prior art]
The liquid crystal display (LCD) is a molecular arrangement that changes the liquid crystal molecules from the initial molecular arrangement to another molecular arrangement using the external electric field and heat quantity. The liquid crystal display is converted into a visual change by a change in optical properties such as birefringence optical rotation, dichroism, and light scattering. In addition, the LCD has the advantage of lower operating voltage and lower power consumption, and is suitable for driving by a large scale integrated circuit. Currently, with the development and advancement of thin film transistor (TFT) technology, it has become increasingly common to use TFTs as LCD display pixels.
[0003]
[Problems to be solved by the invention]
FIG. 1 shows a part of a general LCD structure. In the case of a TFT type LCD, a matrix is constituted by a plurality of TFTs (thin film transistors) on a transparent substrate (not shown). Share one pixel. Based on the characteristics of the TFT, the drain-source current ( _IDS discharge current) at the time of turning off is much smaller than that of a general MOSFET, and the general numerical value is 10 ⁻¹¹ to 10 ⁻¹² ampere (A) or less. It is. However, this also forms a drawback of TFT LCDs. That is, when the LCD is turned off, since the discharge current is small, the discharge time (discharge time = t _d ) of the voltage V _SD between the source and drain becomes longer, causing a phenomenon that an image remains on the LCD. It was.
[0004]
In FIG. 2, when the TFT type liquid crystal display of the prior art is turned off, the gate / drain voltage (V _GD ), the source / drain voltage (V _SD ), the common electrode voltage (V _COM ) of each pixel (that is, each TFT). ) And the discharge time (t _d ), the LCD is turned _off at time t = t _off . Then, it can be seen that the source / drain voltage V _SD becomes 0 V only after a very long discharge time t _d has elapsed. Therefore, the discharge current I _DS is turned if small enough as source-drain voltage V _SD of the discharge time is longer small, the time remaining in the image is long.
[0005]
Therefore, a first object of the present invention is to provide a residual image of a liquid crystal display that can reduce the discharge time of charges accumulated in the liquid crystal by applying a pulse voltage to the TFT electrode when the LCD is turned off. It is to provide a way to reduce.
[0006]
[Means for Solving the Problems]
In order to solve the above problems and achieve a desired object, a method of reducing a residual image of a liquid crystal display according to the present invention is to form a matrix composed of a plurality of transistors on a transparent substrate. Each transistor includes a gate, a drain, and a source, and the liquid crystal is connected between the source and the common electrode. When the transistor is turned off, a pulse voltage is applied to the drain or the common electrode in the liquid crystal, By shortening the discharge time of the source-drain voltage between the drain and the source of each transistor, the discharge time of the charge accumulated in the liquid crystal can be shortened, and thereby the image remaining time after the LCD is turned off Can be greatly shortened.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
Based on the above means, when the liquid crystal display is turned off, by applying a pulse voltage to one electrode of the thin film transistors constituting the liquid crystal display, the discharge current between the drain and the source of each thin film transistor is instantaneously changed. At the same time as increasing the voltage between the drain and source or between the gate and drain, the residual time of the image can be shortened by shortening the discharge time of the drain-source current when it is off It is.
[0008]
【Example】
Preferred embodiments according to the present invention will be described below with reference to the drawings.
FIG. 3 shows one transistor of the LCD pixel matrix, and one TFT has a gate, a drain, and a source. One liquid crystal LC is connected between the common electrode COM and the source. Also it is connected a liquid crystal LC and one capacitor C _ST in parallel. In general, the liquid crystal LC also has an equivalent capacitance value _CLC .
[0009]
A pulse voltage that achieves the object of the present invention is generated by a pulse generator 10. The pulse generator 10 generates a pulse signal when an LCD off signal is received. The purpose of this pulse signal can be achieved regardless of whether it is applied to the gate or drain of the TFT or the common electrode, so these three types of situations will be described below.
[0010]
The output signal of the pulse generator 10 in FIG. 3 is input to the common electrode COM. When selecting different electrodes, it is necessary to input the output signal of the pulse generator 10 to the gate or drain, respectively.
[0011]
<First embodiment>
3 and 4, the case where a pulse voltage is first applied to the common electrode will be described.
After the LCD is turned off, the pulse voltage V _P1 is applied to the common electrode COM. The pulse voltage _{V P1} is because they are electrically connected to the source of the TFT via the liquid crystal LC and capacitor _{C ST,} increases the source voltage _{V S.} As the source voltage V _S increases, the source / drain voltage V _SD also increases, and the drain / source current I _DS also increases, so that the discharge time t _d can be shortened. Thereby, the electric charge accumulated in the liquid crystal can be released in a short time. Therefore, it is possible to solve problems that due to the residual image conventional discharge time t _d is too long a.
[0012]
In FIG. 4, when the pulse voltage V _P1 is applied to the common electrode, the source / drain voltage V _SD also generates the corresponding pulse voltage V _P1 ′, but the pulse width of the pulse voltage V _P1 ′ is very small. The source / drain voltage V _SD is immediately reduced to 0V. That is, the charge accumulated in the liquid crystal LC can be instantaneously released. For example, if the width of the pulse voltage V _P1 is about 1 second, the drain-source current _IDS is also increased to 10 ⁻¹¹ or more or further increased at the time of OFF, so the discharge time t _d is shortened to 1 second or less. Can do.
[0013]
<Second embodiment>
Next, a case where a pulse voltage is applied to the gate of the TFT will be described.
In FIG. 5, after the LCD is turned off, a pulse voltage V _p2 (which can be a positive pulse) is applied to the gate. At this time, the gate-drain voltage V _GD and the source-drain voltage V _SD also increase, and the drain-source current I _DS also increases. That is, the discharge speed of the source / drain voltage _VSD is accelerated, and the discharge time is shortened. As a result, the charges accumulated in the liquid crystal LC are released in a short time. Therefore, it is possible to solve the problems of the prior art residual image which has been generated by the discharge time t _d is too long a.
[0014]
As shown in FIG. 5, when the pulse voltage V _p2 is applied to the gate, the corresponding pulse voltage V _p2 ′ is generated even in the gate-drain voltage V _GD . Therefore, the source / drain voltage V _SD is immediately reduced to 0 V, and the charge accumulated in the liquid crystal LC can be released.
[0015]
<Third embodiment>
Finally, a case where a pulse voltage is applied to the drain of the TFT will be described.
In FIG. 6, after the LCD is turned off, a pulse voltage V _p3 (which can be a negative pulse) is applied to the drain. As a result, the gate-drain voltage V _GD is increased, a corresponding pulse voltage V _p3 ′ (in this third embodiment, a positive pulse) is generated, and the drain-source current I _DS is also increased. That is, the discharge speed of the source / drain voltage _VSD is accelerated, and the discharge time is shortened. As a result, the charges accumulated in the liquid crystal LC are released in a short time. Therefore, it is possible to solve the problem of the residual image that has occurred due to the discharge time td of the prior art being too long. For example, if the width of the pulse voltage V _p3 is about 1 second, the drain-source current _IDS is also increased to 10 ⁻¹¹ or more at the time of OFF, so that the discharge time t _d can be shortened to 1 second or less. it can.
[0016]
As shown in FIG. 6, when a negative pulse voltage V _p3 is applied to the drain, the gate-drain voltage V _GD also generates a corresponding positive pulse voltage V _p3 ′. Therefore, the source / drain voltage V _SD is immediately reduced to 0 V, and the charge accumulated in the liquid crystal LC can be released.
[0017]
As can be seen from the above description, when the LCD is turned off, applying a pulse voltage to the common electrode or gate or drain of the TFT increases the source / drain voltage V _SD and the drain / source current I _DS. Thus, the discharge time of the source / drain voltage _VSD can be shortened. Therefore, since the charge accumulated in the liquid crystal LC can be immediately released, the problem that the image on the LCD remains can be solved. For example, if the width of the pulse voltage V _P1 is about 1 second, the drain-source current _IDS is also increased to 10 ⁻¹¹ or more or further increased at the time of OFF, so the discharge time t _d is reduced to 1 second or less. Can do.
[0018]
<Fourth embodiment>
In FIG. 7, a circuit configuration according to the method of the present invention will be described. Note that the electrode to which the pulse voltage is applied should be determined by the LCD manufacturer or the user. A switch means 22 is provided between the pulse generator 20 and the TFT matrix 24, and the switch means 22 selects a pulse voltage to be applied to any one of the gate, the drain and the common electrode based on the selection signal SEL. Each of the gate and drain and the common electrode of the TFT matrix 24 described above is connected to the pulse generator 20 via the switch means 22, so that an optimum electrode is selected and a pulse voltage is applied to the LCD. The problem of the residual image after being turned off can be effectively solved.
[0019]
As described above, the present invention has been disclosed in the preferred embodiments. However, the present invention is not intended to limit the present invention, and is within the scope of the technical idea of the present invention so as to be easily understood by those skilled in the art. Since appropriate changes and modifications can be naturally made, the scope of protection of the patent right must be determined on the basis of the scope of claims and an area equivalent thereto.
[0020]
【The invention's effect】
With the above configuration, the method for reducing the residual image of the liquid crystal display according to the present invention is compared with the prior art by applying a pulse voltage to the gate or drain of the TFT or the common electrode when the LCD is turned off. The discharge time of the source / drain voltage of the TFT can be greatly shortened, and the residual image can be reduced. Therefore, the industrial utility value is high.
[Brief description of the drawings]
FIG. 1 is a circuit diagram showing a thin film transistor matrix constituting a pixel.
FIG. 2 is a coordinate diagram showing voltage changes between a gate / drain voltage, a source / drain voltage, and a common electrode voltage of a thin film transistor that is a pixel before and after turning off a liquid crystal display according to the prior art.
FIG. 3 is a circuit diagram showing a first embodiment according to the method of the present invention.
FIG. 4 is a coordinate diagram showing a first embodiment according to the present invention.
FIG. 5 is a coordinate diagram showing a second embodiment according to the present invention.
FIG. 6 is a coordinate diagram showing a third embodiment according to the present invention.
FIG. 7 is a circuit diagram showing a fourth embodiment according to the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Pulse generator 20 Pulse generator 22 Switch means 24 TFT matrix LC Liquid crystal

Claims (6)

In a liquid crystal display having a plurality of transistors, each transistor including a gate, a drain, a source, and a liquid crystal, and connecting the source to a common electrode,
When the liquid crystal display is turned off, a pulse voltage is applied to the common electrode in the liquid crystal to shorten the discharge time of the source / drain voltage between the drain and source of the plurality of transistors. A method for reducing the residual image of a liquid crystal display. 2. The method of reducing a residual image of a liquid crystal display according to claim 1, wherein the pulse voltage is a positive pulse voltage. In a liquid crystal display having a plurality of transistors, each transistor including a gate, a drain, a source, and a liquid crystal, and connecting the source to a common electrode,
When the liquid crystal display is turned off, a pulse voltage is simultaneously applied to the drains of the plurality of transistors, and a discharge time of the source / drain voltage between the drains and sources of the plurality of transistors is described. A method for reducing the residual image of a liquid crystal display. 4. The method of reducing a residual image of a liquid crystal display according to claim 3, wherein the pulse voltage is a negative pulse voltage. 4. The method of reducing a residual image of a liquid crystal display according to claim 1, wherein the plurality of transistors are thin film transistors. A pulse generator, a plurality of thin film transistors, in a liquid crystal display comprising a switch means for connecting said pulse generator to either all of the drain and shared electrode in said plurality of thin film transistors,
Generating an off signal when turning off the liquid crystal display; and
The pulse generator generates a pulse voltage based on the off signal, and the switch means is connected to any one of the drain and the common electrode, and the pulse voltage is converted to the pulse voltage. Applying to one of the drain and the common electrode of the plurality of thin film transistors, the discharge time of the source-drain voltage between the drain and the source of the plurality of thin film transistors is shortened. And a method for reducing a residual image of a liquid crystal display.

Images