JPH10282937A - Method of driving liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent flickering from being generated even when a liquid crystal display device displays a fixed pattern like a checker. SOLUTION: In this active matrix type of a liquid crystal display device, TFT 6 connected with pixel electrodes 7-22 are formed in the neighborhood of intersectional parts of gate bus lines 4 and data bus lines 5 which are formed on a substrate in a matrix form, and liquid crystal is held between the pixel electrodes and counter electrodes, and transmittance of the liquid crystal is controlled according to the voltage applied to the pixel electrodes 7-22. A gate bus line 4 is selected so that an interlace drive is performed on a screen, and there are limited up to such two successive pixels as the voltage applied on the horizontally adjacent pixel electrodes 7, 8 always has an opposite polarity to a counter electrode voltage and the voltage applied on the vertically adjacent pixel electrodes 7, 15 has a same polarity as the counter electrode voltage.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for driving a liquid crystal display device, and more particularly to a method for driving a thin film field effect transistor (hereinafter referred to as a thin film field effect transistor).
(Hereinafter referred to as TFT).

[0002]

2. Description of the Related Art In a conventional active matrix type liquid crystal display device, display flicker called "flicker" has been a problem. The principle of generation of flicker will be described with reference to FIGS.

FIG. 3 is a diagram showing a relationship between voltages applied to a liquid crystal display device, and shows a relationship between a pixel electrode voltage and a counter electrode voltage. In FIG. 3, the voltage 23 of the pixel electrode
Changes the waveform into a rectangle between the voltage values V1 and V2.
The voltage 24 of the counter electrode takes a constant value Vcom. Here, V1 is a voltage value when a positive voltage is applied to the pixel electrode with respect to the common electrode voltage, and V2 is a negative voltage applied to the pixel electrode with respect to the common electrode voltage. It is the voltage value in the case.

FIG. 4 is a diagram showing a polarity pattern of an applied voltage in a method of driving a liquid crystal display device according to a first conventional example. The voltage polarity of a pixel electrode with respect to a counter electrode voltage in a part of a display portion of the liquid crystal display device is shown. Shows a pattern. 4, a first frame is a pixel pattern when the voltage V1 shown in FIG. 3 is applied, and a second frame is a pixel pattern when the voltage V2 shown in FIG. 3 is applied.

[0005] In the driving method shown in FIG. 4, one cycle is composed of two frames of a first frame and a second frame.
First, in the first frame, a positive voltage is applied to all the pixel electrodes, and a voltage (V1−Vcom) is applied to the liquid crystal. Next, in the second frame, a negative voltage is applied to all the pixel electrodes, and a voltage (Vcom-V2) is applied to the liquid crystal. Hereinafter, by repeating this operation, the liquid crystal is driven by applying an AC voltage.

The transmittance of the liquid crystal corresponds to the applied voltage. In FIG. 3, | V1-Vcom | = | Vcom
-V2 |, the transmittance does not change between the periods t1 and t2 shown in FIG. However, in general, | V1−Vcom | and | Vcom−V2 due to the parasitic capacitance of the TFT for applying a voltage to the pixel electrode and the dielectric anisotropy of the liquid crystal itself.
The two potential differences | are rarely equal. For this reason, the voltage value applied to the liquid crystal is different between the first frame and the second frame, and the transmittance changes at half the frame frequency in the transmittance. When this frequency is high, a change in transmittance cannot be confirmed by human eyes, but the frame frequency of a liquid crystal display device which is usually used is about 60 Hz, which changes the transmittance to about 30 Hz. The eyes will see it as flicker.

To eliminate this phenomenon, for example, Nikkei BP
A method has been proposed as shown on page 121 of "Flat Panel Display 1993" issued by the company.

FIG. 5 is a diagram showing a polarity pattern of an applied voltage in a method of driving a liquid crystal display device according to a second conventional example, and shows an operation principle disclosed in the above-mentioned document. The driving method shown in FIG. 5 is also similar to the driving method shown in FIG.
It has a cycle. The difference from the method shown in FIG. 4 is that the voltage polarities of the pixel electrodes adjacent vertically and horizontally are inverted. As a result, when the display is viewed, the transmittance is averaged, and the same transmittance is obtained in either of the two frames, so that a flicker-free display can be obtained.

[0009]

The driving method shown in FIG. 5 has a high flicker canceling effect in the case of uniform gray display over the entire surface. However, in the case of a fixed display pattern corresponding to a point where the polarity of the pixel electrode voltage is inverted as shown in FIG. 5, for example, there is a problem that the effect of reducing flicker is significantly reduced. Such a fixed display pattern hardly appears when displaying a moving image, but when a liquid crystal display device is used as an output device of a personal computer employing Windows as an operating system whose demand has been rapidly increasing in recent years. Since the background graphics have become more complicated than the display of solid black when the previous MS-DOS was used, there is a high possibility that such a fixed display pattern is displayed.
Accordingly, the possibility of occurrence of flicker is increased accordingly.

In view of the above, the present invention is applicable not only when displaying the entire surface of the liquid crystal display device in black or gray, which is the same halftone display, but also when displaying a fixed pattern such as a checkered pattern. An object is to prevent the occurrence of flicker.

[0011]

According to a method of driving a liquid crystal display device of the present invention, a plurality of gate bus lines and a plurality of data bus lines parallel to each other are formed in a matrix on a substrate. A thin-film field-effect transistor is formed near each intersection of the gate bus line and the data bus line, and a pixel electrode is connected to each of the thin-film field-effect transistors. An active matrix type liquid crystal display device in which liquid crystal is sandwiched between the liquid crystal display device and the transmissivity of the liquid crystal is controlled in accordance with a voltage applied to the pixel electrode, wherein interlaced driving is performed on a screen of the liquid crystal display device. The gate bus lines are selected such that the voltage applied to the pixel electrodes arranged in the horizontal direction and adjacent to the pixel bus lines is selected. The polarities with respect to the voltage of the counter electrode are always opposite to each other, and the polarities of the voltages applied to the adjacent pixel electrodes arranged in the vertical direction with respect to the voltage of the counter electrode are the same. 2 pixels or less.

The driving method of the liquid crystal display device according to the present invention is as follows.
The horizontal direction may be a direction parallel to the gate bus line, and the vertical direction may be a direction parallel to the data bus line.

By using such a driving method, it is possible to change the pattern in which the polarity of the pixel electrode voltage is inverted and its position at the cycle of the frame frequency.

[0014]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram showing a polarity pattern of an applied voltage in a method of driving a liquid crystal display device according to an embodiment of the present invention, and shows a voltage polarity of a pixel electrode with respect to a counter electrode voltage in a part of a display portion of the liquid crystal display device. Is shown. In the display unit shown in FIG. 1, the pixels in the vertical direction are the k-th (k is a positive integer) to (k + 3) region from the upper side, and the pixels in the horizontal direction are the m-th (m is (Positive integer) to (m + 3) th region.

In the first frame shown in FIG. 1A, the hatched pixel electrode 1 indicates a pixel electrode to which a gate bus line is selected and a voltage is applied during the frame period. The positive pixel electrode 2 (+) is a pixel in which the pixel electrode voltage is positive with respect to the counter electrode voltage. The negative pixel electrode 3 (-) is a pixel in which the pixel electrode voltage is negative with respect to the counter electrode voltage.

FIG. 1A shows a state in which the k-th and (k + 2) -th pixel electrodes in the vertical direction are selected in the first frame period, and the voltages of the pixels are inverted. Numbers in FIG. 1A indicate the order in which the voltage supplied from the data bus line is applied to the pixel electrode in the illustrated area, and, and are synchronized with each other. Writing has been performed. When writing to the next pixel electrode is performed, the pixel voltage polarity is always inverted.

Similarly, FIG. 1 (b) shows the vertical direction (k +) not selected in FIG. 1 (a) during the second frame period.
This shows a state in which the 1) th and (k + 3) th pixel electrodes are selected, and the voltages of the pixel electrodes are inverted.
At this time, the order of writing to the pixel electrodes is also shown in FIG.
Is the same as

FIG. 1C shows the state of FIG. 1 during the third frame period.
The state where the voltage polarity of the pixel electrode selected in (a) is inverted is shown. FIG. 1D shows a state in which the voltage polarity of the pixel electrode selected in FIG. 1B is inverted during the fourth frame period.

Thus, the odd frames (first and third frames) and the even frames (second and fourth frames)
The voltage applied to the pixel is such that the polarity of the pixel electrode voltage adjacent in the horizontal direction is always reversed, and the voltage of the pixel electrode voltage adjacent in the vertical direction that has the same polarity is up to two consecutive pixels.

That is, the voltage polarity applied to each pixel is 4
One cycle in a frame, one pixel in the horizontal direction and two pixels in the vertical direction
A set of checkered patterns is formed with the pixels. Then, a voltage is applied such that the polarity and position of each set are different in each frame.

[0022]

Next, an embodiment in which the present invention is applied to a VGA panel having 480 pixels in the vertical direction and 1920 pixels in the horizontal direction (640 × RGB =) will be described in detail with reference to the drawings.

FIG. 2 is a plan view showing the structure of the liquid crystal display device according to one embodiment of the present invention, and shows a plan view of a substrate on which TFTs are formed. The substrate shown in FIG. 2 includes a gate bus line 4, a data bus line 5,
It has an FT 6 and pixel electrodes 7 to 22. In FIG. 2, the VGA
The M-th and (M + 1) -th data bus lines 4, the N-th to (N + 7) -th gate bus lines 5, and the intersections of the data bus lines 4 and the gate bus lines 5 in the panel. TFT 6 and pixel electrodes 7 to 2
Only the portion 2 is enlarged.

In the first frame period, the Nth, (N +
The (1) -th, (N + 4) -th and (N + 5) -th gate bus lines 4 are sequentially selected. Correspondingly, M
From the data bus line 5 to the pixel electrodes 7, 8, 9, 1
A voltage is applied in the order of 0, and a voltage is applied in the order of the pixel electrodes 11, 12, 13, and 14 from the (M + 1) -th data bus line 5. At this time, the polarity of the pixel electrode with respect to the counter electrode voltage is set to be positive, negative, positive, and negative.

In the second frame period, the (N + 2) th,
The (N + 3) -th, (N + 6) -th, and (N + 7) -th gate bus lines 4 are sequentially selected. Correspondingly, from the M-th data bus line 5 to the pixel electrodes 15, 1
The voltages are applied in the order of 6, 17, and 18, and the (M + 1) -th data bus line 5 to the pixel electrodes 19, 20, 2
Voltages are applied in the order of 1 and 22. At this time, the polarity of the pixel electrode with respect to the counter electrode voltage is set in the order of negative, positive, negative, and positive.

In the third frame period, voltages are written to the pixels in the same order as in the first frame period, but the voltage polarities of all the pixel electrodes are inverted from those in the first frame period.

In the fourth frame period, voltages are written to the pixels in the same order as in the second frame period, but the voltage polarities of all the pixel electrodes are inverted from those in the second frame period.

[0028]

As described above, the effect of the present invention is not only when the entire surface of the liquid crystal display device displays black or gray such as the same halftone display, but also when a fixed pattern such as a checkered pattern is displayed. This means that flicker can be prevented even when displaying.

The reason for this is that, assuming that two pixels are one set, the polarity of the voltage applied to the adjacent set of pixels is inverted, and the set of pixels having the same polarity is different in each frame period.

[Brief description of the drawings]

FIG. 1 is a diagram showing a polarity pattern of an applied voltage in a driving method of a liquid crystal display device according to an embodiment of the present invention.

FIG. 2 is a plan view showing a configuration of a liquid crystal display device according to one embodiment of the present invention.

FIG. 3 is a diagram illustrating a relationship between voltages applied to a liquid crystal display device.

FIG. 4 is a diagram showing a polarity pattern of an applied voltage in a method of driving a liquid crystal display device according to a first conventional example.

FIG. 5 is a diagram showing a polarity pattern of an applied voltage in a method of driving a liquid crystal display device according to a second conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Selected pixel electrode (hatched part) 2 Positive pixel electrode 3 Negative pixel electrode 4 Gate bus line 5 Data bus line 6 TFT 7-22 Pixel electrode 23 Pixel electrode voltage 24 Counter electrode voltage

Claims (2)

[Claims] 1. A plurality of gate bus lines parallel to each other and a plurality of data bus lines parallel to each other are formed in a matrix on a substrate, and a plurality of gate bus lines and a plurality of parallel data bus lines are formed at intersections of the gate bus lines and the data bus lines. A thin-film field-effect transistor is formed in the vicinity, a pixel electrode is connected to each of the thin-film field-effect transistors, and a liquid crystal is sandwiched between the pixel electrode and the counter electrode, and is applied to the pixel electrode. In the active matrix type liquid crystal display device in which the transmittance of the liquid crystal is controlled according to the applied voltage, the gate bus lines are selected so that interlace driving is performed on the screen of the liquid crystal display device, and the gate bus lines are arranged in a horizontal direction. The polarity of the voltage applied to the adjacent pixel electrode with respect to the voltage of the counter electrode is always opposite to each other. A liquid crystal display characterized in that the polarity of the voltage applied to the adjacent pixel electrodes arranged in the vertical direction with respect to the voltage of the counter electrode is two or less pixels having the same polarity continuously. How to drive the device. 2. The method according to claim 1, wherein the horizontal direction is a direction parallel to the gate bus line, and the vertical direction is a direction parallel to the data bus line.