KR100531478B1 - Liquid crystal display panel and method of dirving the same - Google Patents

Abstract

The present invention provides a liquid crystal display panel and a driving method thereof capable of minimizing the magnitude of the common voltage ripple when displaying a specific pattern by a dot inversion method.

A liquid crystal display panel according to the present invention includes a dot inversion liquid crystal display panel which drives a polarity of a data signal in a dot unit, the liquid crystal display panel comprising: a plurality of gate lines and data lines; Liquid crystal cells formed at intersections of the gate lines and the data lines; A plurality of common voltage lines formed in parallel with the gate lines; Each of the liquid crystal cells includes a liquid crystal capacitor comprising a pixel electrode and a common electrode interposed between liquid crystals; A first storage capacitor comprising a pixel electrode having an insulating film interposed therebetween and a previous gate line; And a second storage capacitor including a pixel electrode with an insulating film interposed therebetween, and a common voltage line included in an adjacent horizontal line.

Description

Liquid crystal display panel and its driving method {LIQUID CRYSTAL DISPLAY PANEL AND METHOD OF DIRVING THE SAME}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device, and more particularly, to a liquid crystal display panel and a driving method thereof, which can minimize a horizontal crosstalk phenomenon generated when a specific pattern is displayed by a dot inversion method.

Conventional liquid crystal display devices display an image by adjusting the light transmittance of the liquid crystal using an electric field. To this end, the liquid crystal display includes a liquid crystal display panel in which liquid crystal cells are arranged in a matrix, and a driving circuit for driving the liquid crystal display panel.

In the liquid crystal display panel, the gate lines and the data lines are arranged to cross each other, and the liquid crystal cells are positioned at the intersections of the gate lines and the data lines. Each of the liquid crystal cells is provided with pixel electrodes and a common electrode for applying an electric field. Each of the pixel electrodes is connected to one of the data lines via a thin film transistor which is a switching element. The gate terminal of the thin film transistor is connected to any one of the gate lines through which the pixel voltage signal is applied to the pixel electrodes of one line. Accordingly, the liquid crystal array between the pixel electrode and the common electrode is changed according to the pixel voltage signal for each liquid crystal cell, thereby adjusting the light transmittance so that the liquid crystal display panel displays an image.

The driving circuit includes a gate driver for driving the gate lines, a data driver for driving the data lines, and a common voltage generator for driving the common electrode. The gate driver sequentially supplies the scanning signal, that is, the gate signal to the gate lines, to sequentially drive the liquid crystal cells on the liquid crystal display panel by one line. The data driver supplies a pixel voltage signal to each of the data lines whenever a gate signal is supplied to any one of the gate lines. The common voltage generator supplies a common voltage signal to the common electrode.

Such liquid crystal display devices are roughly classified into twisted nematic (TN) mode in which a vertical electric field is applied and in plane switch (IPS) mode in which a horizontal electric field is applied according to the direction of the electric field driving the liquid crystal.

The TN mode is a mode in which a liquid crystal is driven by a vertical electric field between a pixel electrode and a common electrode disposed to face the upper and lower substrates, and has a large aperture ratio but a narrow viewing angle.

The IPS mode is a mode in which a liquid crystal is driven by a horizontal electric field between a pixel electrode and a common electrode arranged side by side on the lower substrate, and has a large viewing angle, but a small aperture ratio.

FIG. 1 is an equivalent plan view of a liquid crystal display panel in a general IPS mode.

The liquid crystal display panel of the IPS mode shown in FIG. 1 includes a thin film transistor TFT formed at each intersection of the data lines DL1 to DLm and the gate lines GL1 to GLn, and a thin film transistor TFT and a common voltage line. The liquid crystal cell connected between (VCOML1-VCOMLm) is provided.

The plurality of gate lines GL0 to GLn and the data lines DL1 to DLm are arranged to cross each other. The common voltage lines VCOML1 to VCOMLn are arranged side by side alternately with the gate lines GL0 to GLn-1. The gate lines GL1 through GLn supply a scan signal, and the data lines DL1 through DLm supply a data signal. The first gate line GL0 of the gate lines GL0 to GLn is for forming the second storage capacitor Cst2 unlike the other gate lines GL1 to GLn and supplies only a gate low voltage. The common voltage lines VCOML1 to VCOMLn supply a reference voltage of the liquid crystal cell Clc in common.

The thin film transistor TFT supplies a data signal from any one of the data lines DL1 to DLm to the liquid crystal cell in response to a scan signal from any one of the gate lines GL1 to GLn. The liquid crystal cell includes a liquid crystal capacitor Clc formed of a pixel electrode and a common electrode formed side by side with a liquid crystal interposed on a lower substrate. The pixel electrode is connected to the thin film transistor TFT, and the common electrode is connected to any one of the common voltage lines VCOML1 to VCOMLn. The liquid crystal cell includes a first storage capacitor Cst1 formed at an overlapping portion of the pixel electrode and the common electrode with an insulating film interposed therebetween, and a second formed at the overlapping portion of the pixel electrode with an insulating film and the previous gate line. The storage capacitor Cst2 is further provided. The first and second storage capacitors Cst1 and Cst2 help to stably maintain the data signal charged in the liquid crystal capacitor Clc during the turn-off period of the thin film transistor TFT. The liquid crystal cell realizes gray scale by controlling the light transmittance by varying the arrangement state of the liquid crystal having dielectric anisotropy according to the charged data signal.

Such a liquid crystal display device uses an inversion such as a frame inversion system, a line column inversion system, or a dot inversion system to drive liquid crystal cells on a liquid crystal display panel. Drive method is used.

The frame inversion scheme reverses the polarity of the data signal supplied to the liquid crystal cells whenever the frame is changed. The line inversion method inverts the polarities of the data signals supplied to the liquid crystal cells in line (low line or column line) units and in frame units. The dot inversion method inverts the data signals supplied to the liquid crystal cells in dot units and inverts them in frame units. Among the inversion driving methods, the dot inversion method has an advantage of providing an image of excellent image quality compared to other frame and line inversion methods. However, the dot inversion driving method has a disadvantage in that a horizontal crosstalk phenomenon occurs when a specific pattern is displayed as shown in FIG.

FIG. 2A is a view showing a specific pattern displayed by the dot inversion driving method, and FIG. 2B is a driving waveform diagram for the specific pattern shown in FIG. 2A.

Each of the liquid crystal cells illustrated in FIG. 2A corresponds to each of the red, green, and blue liquid crystal cells (R, G, and B). The red, green, and blue liquid crystal cells R, G, and B are arranged side by side in a stripe shape. As the liquid crystal cells R, G, and B are driven in a dot inversion method, polarities of the data signals are reversed as they progress in the horizontal direction and polarities of the data signals as they progress in the vertical direction.

In particular, in the normal black mode, the liquid crystal cells R, G, and B display a specific pattern, that is, a vertical stripe pattern, in which the middle gray (for example, 127 gray) and the black gray alternate in column line units.

To this end, the data signal Vd supplied to the i-th horizontal line Hi may correspond to the data signal Vd_127 corresponding to 127 gray and the black gray based on the common voltage Vcom as shown in FIG. 2B. The data signals Vd_0 are alternately supplied with different polarities. Also, as illustrated in FIG. 2B, the data signal Vd supplied to the i + 1th horizontal line Hi + 1 also corresponds to the data signal Vd_127 and black gray corresponding to 127 gray based on the common voltage Vcom. The corresponding data signals Vd_0 are alternately supplied with different polarities. Here, the data signal Vd supplied to the i + 1 th horizontal line Hi + 1 has a polarity opposite to that of the data signal Vd supplied to the i th horizontal line Hi.

In this case, since the average level of the data signal supplied to the i-th horizontal line Hi is greater than the negative level relative to the common voltage Vcom, the common voltage Vcom is shown in FIG. 3. It will rise with a relatively large peak in the positive direction. Subsequently, since the average level of the data signal supplied to the i + 1th horizontal line Hi + 1 is greater than the negative polarity level based on the common voltage Vcom, the common voltage (as shown in FIG. Vcom) goes down with a relatively large peak in the negative direction. When the data signal for displaying a specific pattern is supplied in horizontal units, the common voltage Vcom is in the positive and negative directions in the horizontal period H as shown in FIG. 3 according to the average level of the data signal. Ripple phenomenon will occur. The common voltage Vcom ripple also affects the peripheral screen extending in the horizontal direction as shown in FIG. 4, thereby generating horizontal crosstalk in the peripheral screen.

4 illustrates horizontal crosstalk due to a specific pattern in a liquid crystal display panel driven by a dot inversion method.

Referring to FIG. 4, when a window 12 displaying a vertical stripe pattern 14, which is a specific pattern, is displayed on a portion of the liquid crystal display panel image display unit 10, the peripheral screen extending in the horizontal direction of the window 12 is also displayed. It can be seen that the horizontal crosstalk pattern 16 in the form of a vertical stripe occurs. This is because the common voltage fluctuates toward the positive polarity or the negative polarity by the vertical stripe pattern 14 displayed in the window 12 in accordance with the average level of the data signal in units of horizontal periods even in the peripheral screen.

For example, when the average level of the data signal in the i-th horizontal line Hi is large due to the vertical stripe pattern 14 displayed in the window 12, the common voltage is shaken with a peak toward the positive polarity. . This ripple phenomenon of the common voltage level is affected as shown in FIG. 5A in the i-th horizontal line Hi extending to the outside of the window 12. In FIG. 5A, the voltage difference between the positive data signal Vdo and the common voltage Vcom is relatively reduced by the common voltage Vcom that is charged toward the positive polarity in the AOD liquid crystal cell charged with the positive data signal Vdo. This makes it look darker in normal black mode. In contrast, the even liquid crystal cell in which the negative data signal Vde is charged is further increased as the voltage difference between the negative data signal Vde and the common voltage Vcom is relatively increased due to the common voltage Vcom shaking toward the positive polarity. It will look bright.

In addition, when the average level of the data signal is negative in the i + 1th horizontal line Hi + 1 due to the vertical stripe pattern 14 displayed in the window 12, the common voltage is shaken with a peak toward the negative polarity. Will be lost. This ripple phenomenon of the common voltage level also affects the i + 1 th horizontal line Hi + 1 extending to the outside of the window 12 as shown in FIG. 5B. In FIG. 5B, the voltage difference between the negative data signal Vdo and the common voltage Vcom is relatively reduced due to the common voltage Vcom that is charged toward the negative polarity of the AOD liquid crystal cell charged with the negative data signal Vdo. This makes it look darker in normal black mode. On the contrary, in the even liquid crystal cell in which the positive data signal Vde is charged, the voltage difference between the positive data signal Vde and the common voltage Vcom is relatively increased due to the common voltage Vcom shaking toward the negative polarity. It will look brighter.

As the common voltage ripple phenomenon caused by the vertical stripe pattern 14 displayed on the window 12 affects the peripheral screen of the window 12, the luminance difference between the odd liquid crystal cell and the even liquid crystal cell as described above is increased. Will occur. As a result, as shown in FIG. 4, horizontal crosstalk patterns 16 such as vertical stripes are generated in the peripheral screen of the window 12, thereby degrading image quality.

Accordingly, an object of the present invention is to provide a liquid crystal display panel and a driving method thereof capable of minimizing the magnitude of the common voltage ripple when displaying a specific pattern in a dot inversion method.

In order to achieve the above object, the liquid crystal display panel according to the present invention is a dot inversion liquid crystal display panel for driving the polarity of the data signal in the unit of a dot, comprising: a plurality of gate lines and data lines; Liquid crystal cells formed at intersections of the gate lines and the data lines; A plurality of common voltage lines formed in parallel with the gate lines; Each of the liquid crystal cells includes a liquid crystal capacitor comprising a pixel electrode and a common electrode interposed between liquid crystals; A first storage capacitor comprising a pixel electrode having an insulating film interposed therebetween and a previous gate line; And a second storage capacitor including a pixel electrode with an insulating film interposed therebetween, and a common voltage line included in an adjacent horizontal line.

The present invention is characterized in that it further comprises a thin film transistor formed at each intersection of the gate line and the data line to drive the liquid crystal cell.

The present invention may further include a third storage capacitor including a pixel electrode having an insulating film interposed therebetween and a common voltage line of the corresponding horizontal line.

In particular, the second storage capacitor may include a pixel electrode having an insulating layer interposed therebetween, and a common voltage line included in the next horizontal line.

In contrast, the second storage capacitor may include a pixel electrode having an insulating layer interposed therebetween and a common voltage line included in the horizontal line of the previous stage.

The second storage capacitor may cancel the common voltage ripple by supplying a common voltage ripple having a polarity opposite to that of the common voltage ripple generated according to the average level of the data signal supplied to the corresponding horizontal line.

A driving method of a liquid crystal display panel according to the present invention is a dot inversion liquid crystal display panel driving method in which a polarity of a data signal is inverted in a dot unit. Supplying a plurality of data signals having; Causing the magnitude of the common voltage ripple generated according to the average level of the data signals to be attenuated by a storage capacitor formed between the common voltage line included in the horizontal line adjacent to the pixel electrode in each of the liquid crystal cells of the corresponding horizontal line. Characterized in that.

Here, the storage capacitor may be attenuated by supplying a common voltage ripple having a polarity opposite to that of the common voltage ripple.

In particular, the storage capacitor is formed between the pixel electrode and the common voltage line included in the next horizontal line to supply a common voltage ripple having opposite polarities.

On the other hand, the storage capacitor is formed between the pixel electrode and the common voltage line included in the previous horizontal line to supply a common voltage ripple of opposite polarity.

In addition, the common voltage ripple is characterized in that the polarity is inverted according to the average level of the data signal supplied to the corresponding horizontal line in units of horizontal periods.

Other objects and advantages of the present invention in addition to the above objects will become apparent from the detailed description of the embodiments with reference to the accompanying drawings.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to FIGS. 6 to 9B.

6 is a plan view equivalently showing a liquid crystal display panel in an IPS mode according to an embodiment of the present invention.

The LCD panel of the IPS mode shown in FIG. 6 includes a thin film transistor TFT formed at each intersection of the data lines DL1 to DLm and the gate lines GL1 to GLn, and a thin film transistor TFT and a common voltage line. The liquid crystal cell connected between (VCOML1-VCOMLm) is provided.

The plurality of gate lines GL0 to GLn and the data lines DL1 to DLm are arranged to cross each other. The common voltage lines VCOML1 to VCOMLn are arranged side by side alternately with the gate lines GL0 to GLn-1. The gate lines GL1 through GLn supply a scan signal, and the data lines DL1 through DLm supply a data signal. The first gate line GL0 of the gate lines GL0 to GLn is for forming the second storage capacitor Cst2 unlike the other gate lines GL1 to GLn and supplies only a gate low voltage. The common voltage lines VCOML1 to VCOMLn supply a reference voltage of the liquid crystal cell Clc in common.

The thin film transistor TFT supplies a data signal from any one of the data lines DL1 to DLm to the liquid crystal cell in response to a scan signal from any one of the gate lines GL1 to GLn.

The liquid crystal cell includes a liquid crystal capacitor Clc formed of a pixel electrode and a common electrode formed side by side with a liquid crystal interposed on a lower substrate. The pixel electrode is connected to the thin film transistor TFT, and the common electrode is connected to any one of the common voltage lines VCOML1 to VCOMLn. The liquid crystal cell realizes gray scale by controlling the light transmittance by varying the arrangement state of the liquid crystal having dielectric anisotropy according to the charged data signal.

The liquid crystal cell includes a first storage capacitor Cst1 formed at an overlapping portion of the pixel electrode and the common electrode with an insulating film interposed therebetween, and a second formed at the overlapping portion of the pixel electrode with an insulating film and the previous gate line. A storage capacitor Cst2 and a third storage capacitor Cst3 are formed on an overlapping portion of the pixel electrode and the next (or previous) common voltage line. The first and second storage capacitors Cst1 and Cst2 help to stably maintain the data signal charged in the liquid crystal capacitor Clc during the turn-off period of the thin film transistor TFT. The third storage capacitor Cst3 reduces the magnitude of the common voltage Vcom ripple generated due to an average level effect of the data signal supplied to the pixel electrode. In other words, the third storage capacitor Cst3 supplies the common voltage Vcom ripple of an adjacent horizontal line having a polarity opposite to that of the current stage common voltage Vcom ripple to the current stage liquid crystal cell. This will significantly reduce the size of the ripple. This is because the polarity of the common voltage Vcom ripple generated in each of the common voltage lines VCOML1 to VCOMLn in the horizontal line unit always has a polarity opposite to that of the adjacent common voltage line.

As described above, the liquid crystal display panel according to the present invention further includes a third storage capacitor Cst3 in which each of the liquid crystal cells is formed between the common voltage line included in the horizontal line adjacent to the pixel electrode. The third storage capacitor Cst3 can suppress horizontal crosstalk due to the common voltage ripple by supplying a common voltage Vcom ripple having opposite polarities to reduce the magnitude of the common voltage Vcom ripple in each of the liquid crystal cells. Will be.

FIG. 7 illustrates a ripple phenomenon of the common voltage Vcom generated according to the average level of the data signal in the horizontal line unit when the vertical stripes pattern is displayed by the dot inversion driving method as illustrated in FIG. 2A.

Referring to FIG. 7, in the liquid crystal display panel according to the present invention, the common voltage Vcom is shaken according to the average level of the data signal in each horizontal period, so that the magnitude of the common voltage Vcom ripple generated in the horizontal period H is zero. It can be seen that the reduction effect of the storage capacitor Cst3, that is, the neutralization action, is significantly reduced compared to the conventional one.

FIG. 8 illustrates a case in which a window 22 displaying a vertical stripe pattern is floated on the liquid crystal display panel illustrated in FIG. 6.

Referring to FIG. 8, when a window 22 displaying a vertical stripe pattern 24 is floated on a portion of the liquid crystal display panel image display unit 20 illustrated in FIG. 6, a peripheral screen extending in the horizontal direction of the window 22 is displayed. It can be seen that the horizontal crosstalk phenomenon does not occur at. This is because the size of the common voltage Vcom ripple generated by the vertical stripes pattern 24 in the window 22 is significantly reduced due to the offset effect of the third storage capacitor Cst3 and thus does not affect the peripheral screen.

For example, even if the average level of the data signal in the i-th horizontal line Hi is large due to the vertical stripe pattern 24 displayed on the window 22, it shakes toward the positive polarity as shown in FIG. 9A. The magnitude of the common voltage Vcom ripple is significantly attenuated by the third storage capacitor Cst3. Accordingly, the ODD liquid crystal cell in which the positive data signal Vdo is charged in the i-th horizontal line Hi extending to the outside of the window 22 and the even liquid crystal cell in which the negative data signal Vde is charged are charged. There is almost no voltage difference.

Further, even when the average level of the data signal is large in the i + 1th horizontal line Hi + 1 due to the vertical stripe pattern 24 displayed in the window 22, as shown in FIG. 9B, the negative polarity is negative. The magnitude of the common voltage Vcom ripple shaking toward the side is significantly attenuated by the third storage capacitor Cst3. Accordingly, an even liquid crystal cell in which an odd liquid crystal cell in which the negative data signal Vdo is charged and a positive data signal Vde in the i + 1 th horizontal line Hi + 1 extending to the outside of the window 22 are charged. There is almost no difference in charging voltage in the cell.

As described above, in the liquid crystal display panel according to the present invention, the size of the common voltage Vcom ripple is remarkably reduced by the third storage capacitor Cst supplying the common voltage Vcom ripples having opposite polarities. Accordingly, horizontal crosstalk due to the common voltage Vcom ripple can be suppressed.

As described above, the liquid crystal display panel and the driving method thereof according to the present invention further include a third storage capacitor Cst3 formed between the pixel electrode and the common voltage line included in the horizontal line adjacent to the common electrode (Vcom) of opposite polarity. Due to the ripple effect, the magnitude of the common voltage Vcom ripple in each of the liquid crystal cells can be reduced. Accordingly, the liquid crystal display panel and the driving method thereof according to the present invention can improve the image quality by suppressing horizontal crosstalk in the peripheral screen as the magnitude of the common voltage ripple is significantly reduced even when a window displaying a specific pattern is displayed. Will be.

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 detailed description of the specification but should be defined by the claims.

1 is a view showing a liquid crystal display panel of a conventional IPS mode.

FIG. 2A illustrates a specific pattern displayed in a dot inversion scheme on the liquid crystal display panel illustrated in FIG. 1, and FIG. 2B illustrates a driving waveform diagram for displaying the specific pattern illustrated in FIG. 2A.

3 is a diagram illustrating a common voltage ripple phenomenon due to the specific pattern shown in FIG. 2A;

4 is a diagram illustrating a horizontal crosstalk phenomenon in a peripheral screen due to a specific pattern displayed in a window of a liquid crystal display panel.

5A and 5B are driving waveform diagrams for specifically explaining the horizontal crosstalk phenomenon shown in FIG. 4;

6 illustrates a liquid crystal display panel according to an exemplary embodiment of the present invention.

FIG. 7 is a diagram illustrating a common voltage ripple phenomenon attenuated when a specific pattern is displayed on the liquid crystal display panel shown in FIG. 6; FIG.

FIG. 8 is a diagram illustrating a case in which a specific pattern is displayed on a window of the liquid crystal display panel shown in FIG.

9A and 9B are driving waveform diagrams of specific liquid crystal cells included in the peripheral screen of the window shown in FIG. 9;

<Description of Symbols for Main Parts of Drawings>

DL1 to DLm: data line GL0 to GLn: gate line

VCOML0 to VCOMLn: Common voltage line TFT: Thin film transistor

Clc: Liquid Crystal Capacitors Cst1, Cst2, Cst3: Storage Capacitors

Hi, Hi + 1: Horizontal line Vcom: Common voltage signal

Vd: pixel voltage signal Vdo: odd pixel voltage signal

Vde: Even pixel voltage signal 10: Image display unit

12: Windows 14: vertical stripes pattern

16: horizontal crosstalk pattern

Claims (11)

In the dot inversion liquid crystal display panel which drives the polarity of the data signal to be inverted in the dot unit, A plurality of gate lines and data lines; Liquid crystal cells formed at intersections of the gate lines and the data lines; A plurality of common voltage lines formed parallel to the gate lines; Each of the liquid crystal cells, A liquid crystal capacitor comprising a pixel electrode and a common electrode with a liquid crystal interposed therebetween; A first storage capacitor comprising the pixel electrode with an insulating film interposed therebetween and a previous gate line; And a second storage capacitor including the pixel electrode with the insulating layer interposed therebetween, and a common voltage line included in a horizontal line before or next to the pixel electrode. The method of claim 1, And a thin film transistor formed at each intersection of the gate lines and the data lines to drive the liquid crystal cell. The method of claim 1, And a third storage capacitor comprising a pixel electrode sandwiching the insulating film and a common voltage line of the horizontal line. delete delete The method of claim 1, The second storage capacitor And canceling the common voltage ripple by supplying a common voltage ripple having a polarity opposite to that of the common voltage ripple generated according to the average level of the data signal supplied to the horizontal line. In a driving method of a dot inversion liquid crystal display panel in which the polarity of the data signal is inverted in the dot unit, Supplying a plurality of data signals having polarities opposite to data signals adjacent in the horizontal direction in any horizontal period; The magnitude of the common voltage ripple generated according to the average level of the data signals is attenuated by the storage capacitor formed between the pixel electrode and the common voltage line included in the previous or next horizontal line in each of the liquid crystal cells of the corresponding horizontal line. And driving the liquid crystal display panel. The method of claim 7, wherein And the storage capacitor is attenuated by supplying a common voltage ripple having a polarity opposite to that of the common voltage ripple. delete delete The method of claim 8, And wherein the common voltage ripple is inverted in polarity according to an average level of a data signal supplied to a corresponding horizontal line in units of horizontal periods.