KR100841327B1 - Liquid crystal display device and driving method for the same - Google Patents

Abstract

An LCD(Liquid Crystal Display) and a driving method for the same are provided to neutralize ions and electrons remaining in upper and lower substrates of the LCD, thereby preventing flickers and afterimages. An LC layer(150) is driven by a voltage difference between first and second electrodes(109,121). A first transistor(160) applies a data signal to the LC layer. A storage capacitor(140) is formed between the first and second electrodes, and maintains voltage applied to the LC layer. A correcting unit(170) conducts the first and second electrodes to be electrically neutral in a section where the first transistor applies no data signal to the LC layer.

Description

Liquid crystal display and its driving method {LIQUID CRYSTAL DISPLAY DEVICE AND DRIVING METHOD FOR THE SAME}

1 shows a cross-sectional view and an equivalent circuit of a conventional general liquid crystal display (LCD) device.

2 is a graph measuring the output of the liquid crystal display device over time using a photosensor.

3 is a circuit diagram schematically showing the configuration of a liquid crystal display device according to an embodiment of the present invention.

FIG. 4 shows an equivalent circuit diagram of the liquid crystal display device according to the embodiment of FIG. 3.

5 shows an embodiment of a method of driving the present liquid crystal display device.

Figure 6 is a graph comparing the flicker characteristics according to the present invention with the conventional invention.

<Description of Symbols for Major Parts of Drawings>

110: upper plate 101: polarizing plate

103: glass substrate 111: black mattress

105: culper filter 109: common electrode

120: lower plate 121: data electrode

123: insulating layer 125: common electrode

127: glass substrate 150: liquid crystal layer

160: the first transistor 170: the second transistor

The present invention relates to a liquid crystal display device, and more particularly, to a liquid crystal display device having a structure for removing flicker and afterimage of the liquid crystal display device.

Recently, a large screen display device has emerged as one of the most important issues. Until now, such a large screen display device has been developed and commercialized such as a direct view liquid crystal display, a plasma display, a projection TV, a projector, and the like. Among these, projection TVs and projectors commonly include a device called an optical engine, and within this optical engine, a cathode ray tube (CRT), a liquid crystal display (LCD), and a DMD, which display signal processed image information. Display devices such as (Digital Micro Device) and Liquid Crystal on Silicon (LCoS) are used. In particular, the projection type display device using liquid crystals such as a transmissive LCD (liquid crystal display device) and an LCoS element has been developed in recent years due to various advantages.

1 shows a cross-sectional view and an equivalent circuit of a conventional general liquid crystal display (LCD) device. Conventionally, the liquid crystal display device includes a liquid crystal 150 and a transistor 160 for driving the liquid crystal between the upper plate 110 and the lower plate 120 as shown in FIG. 113) and an adhesive portion 115 for coupling the upper plate and the lower plate. Specifically, the upper plate 110 includes a polarizing plate 101, a glass substrate 103, a black mattress 111, a culffer filter 105, and a common electrode 109. The lower plate 120 includes a data electrode 121, The insulating layer 123, the common electrode 125, and the glass substrate 127 are formed, and the transistor 160 is electrically connected between the source electrode and the drain electrodes 163 and 165 by the gate electrode 161. . The liquid crystal display displays an image by adjusting the amount of light output in the direction of the upper panel 110 by adjusting the liquid crystal according to the input data of the backlight (not shown) that emits light from the rear surface of the lower panel 120.

If such a circuit is simply represented as an equivalent circuit, it can be represented as shown in FIG. When the signal of the gate line is turned on, the signal input to the data line is applied to the liquid crystal and the capacitor. That is, a voltage equal to the difference between the applied image signal and the common voltage is applied to the liquid crystal, and the capacitor serves to maintain the applied voltage for a predetermined time even when the signal is turned off by the gate line.

However, such a liquid crystal display has a disadvantage in that an afterimage remains on the screen when a still image is used for a long time.

2 is a graph measuring the output of the liquid crystal display device over time using a photosensor. Although a normal liquid crystal display device should have a constant light output value as shown in FIG. 2 (a) even though time passes, the conventional liquid crystal display device has a time elapsed as shown in FIG. Depending on the light output is also repeated. This difference in output is called flicker, and the larger the flicker, the lower the image quality.

If an electric field in the same direction is continuously applied to the liquid crystal, the liquid crystal material deteriorates, thereby periodically inverting the polarity of the data signal with respect to the common voltage. That is, pixel voltages having positive polarity and negative polarity are alternately applied. In this case, the optimum common voltage is defined as the center value between the positive and negative pixel voltages, but a deviation occurs between the optimum common voltage and the actual common voltage applied to the actual common electrode. As a result, the levels of the positive pixel voltage and the negative pixel voltage are different, and as a result, flicker occurs on the screen. In addition, if the deviation persists, residual DC components are generated, and as a result, residual images due to liquid crystal fatigue are generated.

SUMMARY OF THE INVENTION An object of the present invention is to provide a high-quality liquid crystal display device that does not generate flicker and afterimage and a method of preventing flicker and afterimage by overcoming the problems of the liquid crystal display device.

In order to achieve the above object, a liquid crystal display device according to the present invention comprises: a liquid crystal layer driven by a voltage difference between a first electrode and a second electrode; A first transistor for applying a data signal to the liquid crystal layer; A sustain capacitor formed between the first electrode and the second electrode to hold a voltage applied to the liquid crystal layer; And a correction unit configured to electrically conduct the first electrode and the second electrode in a section in which the first transistor does not apply a data signal to the liquid crystal layer.

The correction unit may include a second transistor for conducting the first electrode and the second electrode of the liquid crystal layer according to a control signal.

The first electrode of the liquid crystal is connected to the common electrode, and the second electrode is connected to the first transistor. Preferably, a data voltage inverted from the common voltage applied to the common electrode is applied to the second electrode.

In addition, the present invention for achieving the above object is a driving method of a liquid crystal display device for driving a liquid crystal layer by the voltage difference between the first electrode and the second electrode, the display step of applying an data signal to the liquid crystal layer to display an image Wow; And a correction step of electrically conducting the first electrode and the second electrode to conduct electrical neutrality in a section in which the data signal is not applied to the liquid crystal layer.

In the display step, a common voltage is applied to the first electrode of the liquid crystal layer, and a data signal is applied to the second electrode. Preferably, a data voltage inverted from the common voltage is applied to the second electrode.

In addition, the liquid crystal display device according to the present invention for achieving the above object comprises a top plate formed with a first electrode; A lower plate on which a second electrode is formed; A liquid crystal layer formed between the upper plate and the lower plate and driven by a voltage difference between the first electrode and the second electrode; A first transistor formed between the upper plate and the lower plate to apply a data signal to the second electrode; And a second transistor for electrically conducting the first electrode and the second electrode to be electrically neutral.

At least one of the first transistor and the second transistor may be a thin film transistor (TFT).

A data voltage inverted from the voltage applied to the first electrode may be applied to the second electrode.

It is preferable that a sustain capacitor is further formed between the upper plate and the lower plate to maintain the voltage of the liquid crystal layer.

The second transistor may be formed on the first transistor.

Other objects, features and advantages of the present invention will become apparent from the following detailed description of embodiments taken in conjunction with the accompanying drawings.

Hereinafter, the configuration and operation of the present invention will be described in detail with reference to embodiments of the liquid crystal display device according to the present invention.

3 is a circuit diagram schematically showing the configuration of a liquid crystal display device according to an embodiment of the present invention.

3 illustrates a minimum unit of pixels in the liquid crystal display panel. According to FIG. 3, the liquid crystal display device according to the present exemplary embodiment includes a liquid crystal layer 150, a first transistor 160, and a second transistor 170 between the upper plate 110 and the lower plate 120. It features.

In detail, the upper plate 110 includes a polarizing plate 101, a glass substrate 103, a black mattress 111, a culffer filter 105, and a common electrode 109. The lower plate 120 includes a data electrode 121. ), An insulating layer 123, a common electrode 125, a glass substrate 127, and the like.

The liquid crystal display displays an image by controlling the amount of light output in the direction of the upper panel 110 by adjusting the voltage of the liquid crystal layer according to the input data of the backlight (not shown) that emits light from the rear of the lower panel 120. do.

The liquid crystal layer 150 varies the transmittance of light emitted from the backlight according to the voltage difference between the common electrode 109 and the data electrode 121.

The first transistor 160 applies an image signal input in the same manner as a conventional liquid crystal display panel to the data electrode 121 according to a control signal. At this time, when the gate electrode 161 of the first transistor 160 is in an on state, an external data signal is transferred from the source electrode 163 to the data electrode 121 through the drain electrode 165. In this case, the source electrode 163 and the drain electrode 165 may be interchanged.

The second transistor 170 is formed between the common electrode 109 and the data electrode 121 to electrically conduct the two electrodes by a control signal so that the upper and lower plates are electrically neutral.

In addition, the lower plate 120 further includes a common electrode 125 under the data electrode 121. The common electrode 125 of the lower plate is electrically connected to the common electrode 109 of the upper plate to have the same voltage. A dielectric, which is an insulating layer, is formed between the common electrode 125 and the data electrode 121 to operate as a single capacitor as a whole. When the voltage of the capacitor 140 is applied to the data electrode 121 through the first transistor 160 to form a voltage difference with the common electrode 109 of the upper plate, the same voltage is also applied to the capacitor 140. After that, even when the voltage applied to the gate electrode of the first transistor 160 is turned off, the voltage is maintained in the capacitor 140 to maintain the voltage of the liquid crystal layer for a predetermined time. Therefore, such a capacitor is also called a holding capacitor.

The liquid crystal display panel configured as described above operates as follows.

When a voltage difference occurs between the data electrode 121 applied by the first transistor and the common electrode 109 to which the common voltage of the upper plate is applied, an electromagnetic field is formed in the liquid crystal layer 150, so that transmittance of the liquid crystal layer is changed. As such, when a voltage difference occurs between the two electrodes, electrons and ions in the panel move to electrodes of different poles. At this time, reverse driving is performed to prevent afterimage caused by deterioration. That is, a data voltage inverted at a predetermined cycle based on the common voltage is applied to the data electrode through the first transistor. In this case, flicker occurs when the potentials of the upper and lower plates are not symmetrical due to an asymmetric accumulation of ions and electrons in the upper and lower plates, and thus the data voltage is not symmetrical with respect to the common electrode. The present invention solves the flicker problem by allowing the upper and lower plates to conduct with the second transistor. That is, when the gate of the second transistor is turned on, the common electrode 109 and the data electrode 121 become conductive so that the ions or electrons accumulated in the electrode and the surrounding insulating layer are electrically neutral. This can significantly reduce the flicker phenomenon caused by the bias of electrons and ions.

4 is an equivalent circuit diagram of the liquid crystal display device according to the embodiment of FIG. 3. As illustrated, the liquid crystal display device according to the present invention includes a liquid crystal layer 150 driven by a voltage difference between a first electrode and a second electrode, a first transistor 160 for applying a data signal to the liquid crystal layer 150, and the And a second transistor 170 that electrically conducts the first electrode and the second electrode to be electrically neutral, and is formed between the first electrode and the second electrode to maintain a voltage applied to the liquid crystal layer for a predetermined time. The capacitor 140 further includes. In this case, the first electrode represents the common electrode and the second electrode represents the data electrode.

5 shows an embodiment of a method of driving the present liquid crystal display device.

The common voltage Vcom is alternately applied to the common electrode 109, and the image signal is applied to the data electrode 121 through the first transistor 160 to display an image in synchronization with the common electrode 109. In this case, when the common voltage Vcom is inverted, the data voltage is also inverted and applied. A predetermined off period Ta exists between the image display section Tb and the image display section Tb. The off period Ta refers to an area where a potential difference does not occur between the common voltage and the video signal. During the off period Ta, the gate of the second transistor 170 is turned on to electrically connect the common electrode and the data electrode to be electrically neutral, thereby preventing flicker.

Figure 6 is a graph comparing the flicker characteristics according to the present invention with the conventional invention. As described above, the present invention can include the second transistor in the liquid crystal display device to significantly reduce flicker generation.

This principle can be applied to all the pixels of the liquid crystal display R, G, and B.

Those skilled in the art will appreciate that various changes and modifications can be made without departing from the technical spirit of the present invention.

Therefore, the technical scope of the present invention should not be limited to the contents described in the embodiments, but should be defined by the claims.

As described above, according to the present invention, there is an effect of providing a liquid crystal display device and a method of driving a liquid crystal display that prevent flicker or an afterimage by neutralizing ions and electrons remaining on the upper and lower plates of the liquid crystal display device.

Claims (13)

A liquid crystal layer driven by a voltage difference between the first electrode and the second electrode; A first transistor for applying a data signal to the liquid crystal layer; A sustain capacitor formed between the first electrode and the second electrode to maintain a voltage applied to the liquid crystal layer; And And a corrector configured to electrically conduct the first electrode and the second electrode so that the first transistor does not apply a data signal to the liquid crystal layer, thereby electrically neutralizing the liquid crystal display device. delete The method of claim 1, wherein the correction unit And a second transistor for conducting the first electrode and the second electrode in response to a control signal. The method of claim 1, Wherein the first electrode of the liquid crystal is connected to the common electrode, and the second electrode is connected to the first transistor. The method of claim 4 And a data voltage inverted from the common voltage applied to the common electrode. In the driving method of the liquid crystal display device for driving the liquid crystal layer by the voltage difference between the first electrode and the second electrode, A display step of displaying an image by applying a data signal to the liquid crystal layer; And And a correction step of electrically conducting the first electrode and the second electrode in a section in which the data signal is not applied to the liquid crystal layer, to thereby electrically neutralize the liquid crystal display device. The method of claim 6, In the displaying step, the common voltage is applied to the first electrode and the data voltage is applied to the second electrode. The method of claim 7, And a data voltage inverting the common voltage to the second electrode. A top plate on which a first electrode is formed; A lower plate on which a second electrode is formed; A liquid crystal layer formed between the upper plate and the lower plate and driven by a voltage difference between the first electrode and the second electrode; A first transistor formed between the upper and lower plates to apply a data signal to the second electrode; And And a second transistor for electrically conducting the first electrode and the second electrode to electrically neutralize the first and second electrodes. The method of claim 9, And at least one of the first transistor and the second transistor is a thin film transistor (TFT). The method of claim 9, And a data voltage inverting the voltage applied to the first electrode to the second electrode. The method of claim 9, And a sustain capacitor for maintaining the voltage of the liquid crystal layer between the upper and lower plates. The method of claim 9, And the second transistor is formed on the first transistor.

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