KR100670143B1 - Driving method of liquid crystal display - Google Patents

Abstract

According to the driving method of the liquid crystal display, one frame is sequentially driven to the first field, the second field, and the third field to which the first light, the second light, and the third light are respectively applied. In this case, the same data voltage of the same polarity is applied two or more times in at least one of the first to third fields. In this way, more accurate gradation can be expressed.

Liquid crystal display, field sequential method, data voltage, subfield

Description

Driving method of liquid crystal display {DRIVING METHOD OF LIQUID CRYSTAL DISPLAY}

1 is a driving waveform diagram of a conventional liquid crystal display.

FIG. 2 is a diagram illustrating a voltage applied to a liquid crystal in a pixel region defined by an i th scan line and a j th data line during one frame.

3 is a diagram illustrating a liquid crystal display according to an exemplary embodiment of the present invention.

4 is a pixel circuit diagram of a liquid crystal display according to an exemplary embodiment of the present invention.

5 is a driving timing diagram of a liquid crystal display according to an exemplary embodiment of the present invention.

FIG. 6 is a diagram illustrating a voltage applied to a liquid crystal in a pixel region defined by an i th scan line Si and a j th data line Dj during one frame.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of driving a liquid crystal display (LCD), and more particularly to a method of driving a liquid crystal display of a field sequential driving method.

Recently, display devices are also required to be lighter and thinner in accordance with light weight and thickness of personal computers and televisions, and flat panel displays such as LCDs are being developed instead of cathode ray tubes (CRTs).

The liquid crystal display applies an electric field to a liquid crystal material having an anisotropic dielectric constant injected between two substrates, and adjusts the intensity of the electric field to adjust the amount of light transmitted from an external light source (backlight) to the substrate. This is a display device which obtains a desired image signal.

Such LCDs are typical of portable flat panel displays, and among them, TFT-LCD using a thin film transistor (TFT) as a switching element is mainly used.

In the TFT-LCD, each pixel may be modeled as a capacitor having a liquid crystal as a dielectric, that is, a liquid crystal capacitor. In the LCD, pixel circuits are formed in a plurality of pixel regions defined by a plurality of data lines and a plurality of scan lines, and each pixel circuit includes a TFT connected between a source electrode and a gate electrode, and a drain voltage and a common voltage between the TFTs. And a liquid crystal capacitor connected thereto.

Such LCDs may be divided into two types, a color filter method and a field sequential driving method, according to a method of displaying a color image.

The color filter LCD forms a color filter layer consisting of three primary colors of red (R), green (G), and blue (B) on one of the two substrates, and displays the amount of light transmitted through the color filter layer. By adjusting, the R, G, and B colors are combined to display a desired image. As such, an LCD displaying an image using a single light source and a three-color color filter layer requires a corresponding unit pixel for each of R, G, and B regions, and thus requires three times as many pixels as those for displaying black and white. . Therefore, in order to obtain a high resolution image, sophisticated manufacturing technology of the panel is required. In addition, such LCDs are cumbersome in manufacturing a separate color filter layer on the substrate, and the luminance is low because the light transmittance of the color filter itself is low.

On the other hand, the LCD of field sequential driving method periodically turns on independent light sources of R, G, and B colors, and applies full color images by applying a color signal corresponding to each pixel in synchronization with the lighting cycle. Get That is, a field sequential driving LCD does not divide one pixel into R, G, and B unit pixels, but instead splits R, G, and B primary colors of light output from the R, G, and B backlights into one pixel. By sequentially displaying the images, images are displayed by using the afterimage effect of eyes.

The operation of the LCD of the field sequential driving method will be described with reference to FIGS. 1 and 2. 1 is a driving waveform diagram of a conventional field sequential driving type LCD, and FIG. 2 is a diagram showing a voltage applied to a liquid crystal in a pixel region defined by an i th scan line and a j th data line during one frame. Here, the liquid crystal corresponds to the liquid crystal capacitor.

 First, as shown in FIG. 1, the LCD of the conventional field sequential driving method is driven by dividing one frame into an R field, a G field, and a B field. In each field, scan signals are sequentially applied to the plurality of scan lines S1 to Sn, and when the TFT is turned on, the data voltage supplied to the corresponding data lines D1 to Dm is applied to each pixel electrode (not shown) through the TFT. do. Then, an electric field corresponding to the difference between the pixel voltage and the common voltage applied to the pixel electrode is applied to the liquid crystal capacitor to transmit light with a transmittance corresponding to the intensity of the electric field. In FIG. 1, a data voltage is applied to the j th data line Dj among the plurality of data lines D1 to Dm.

As described above, since the LCD of the field sequential driving type drives one frame into the R field, the G field, and the B field, the liquid crystal should have a higher response speed than the color filter type LCD. In general, the liquid crystal is a polymer material and does not respond quickly to changes in the electric field, and the liquid crystal molecules are in a stable state for a certain time. The delay of the response time is a problem in that the image quality is degraded when the moving image is implemented by leaving an afterimage on the screen. Therefore, a V-shape liquid crystal having a fast response speed is suitable for a field sequential driving LCD.

The V-Shape type liquid crystal has an ether introduced near the chiral center, and has a fast response speed of about several hundred microseconds that can realize a moving image. In addition, the contrast ratio is 300 or more, continuous gray scale representation, a wide viewing angle (70 degrees) is possible, and the orientation is excellent.

In general, in one pixel area, the liquid crystal must maintain a constant voltage for one frame or one field so that gray scale can be accurately realized. By the way, in the V-shape type liquid crystal, the liquid crystal rotates due to voltage inversion, and as shown in FIG. 2, the voltage holding ratio applied to the liquid crystal drops over time, so that accuracy in gray scale expression is degraded. There is a problem.

 It is an object of the present invention to provide a liquid crystal display and a driving method thereof capable of improving the accuracy of gradation representation.

According to an aspect of the present invention, there is provided a liquid crystal display device comprising a plurality of data lines for transmitting a data voltage representing an image, a plurality of scan lines for transmitting a scan signal, and a plurality of pixels defined by the data lines and the scan lines. A drive method is provided. The driving method sequentially drives one frame into a first field, a second field, and a third field to which the first light, the second light, and the third light are respectively applied, and at least one of the first to third fields. The field is divided into a plurality of subfields including first and second subfields, and at least one of the first to third fields is divided into the plurality of scan lines in the first subfield. Sequentially applying a first scan signal and applying a first data voltage to the data line in response to the first scan signal, and sequentially applying a second scan signal to the plurality of scan lines in a second subfield; And applying a second data voltage to the data line in response to the second scan signal. In this case, the first data voltage and the second data voltage are the same data voltage of the same polarity.

In the first to third fields, the first and second data voltages may be inverted for each field, and the first, second, and third lights may be red, green, and blue, respectively.

According to another aspect of the invention, a liquid crystal display device comprising a plurality of data lines for transmitting a data voltage representing an image, a plurality of scanning lines for transmitting a scanning signal, the data line and a plurality of pixels defined by the scanning lines A driving method of is provided. In this driving method, one frame is divided into a plurality of fields, and at least one of the plurality of fields is divided and driven into a plurality of sub-fields including first and second subfields. At least one field, sequentially applying a first scan signal to the plurality of scan lines in the first subfield and applying a first data voltage to the data line in response to the first scan signal; And sequentially applying a second scan signal to the plurality of scan lines in two subfields, and applying a second data voltage to the data line in response to the second scan signal.

The first and second data voltages may be inverted for each frame.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the present invention. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention. In the drawings, parts irrelevant to the description are omitted in order to clearly describe the present invention. Like parts are designated by like reference numerals throughout the specification.

Now, a method of driving a liquid crystal display according to an exemplary embodiment of the present invention will be described in detail with reference to the accompanying drawings.

First, a schematic structure of a liquid crystal display according to an exemplary embodiment of the present invention will be described in detail with reference to FIG. 3.

3 is a diagram illustrating a liquid crystal display according to an exemplary embodiment of the present invention.

As shown in FIG. 3, the liquid crystal display according to the exemplary embodiment of the present invention includes a liquid crystal display panel 100, a scan driver 200, a data driver 300, a timing controller 400, and a gray voltage generator 500. , Light source controller 600 and light emitting diodes 700a, 700b, 700c.

The liquid crystal display panel 100 includes a plurality of data lines D1 to Dm extending in the vertical direction, a plurality of scan lines S1 to Sn extending in the horizontal direction, and a plurality of pixel circuits 110. The scan lines S1 to Sn transmit a scan signal for selecting the pixel circuit to the pixel circuit 110. The data lines D1 to Dm transfer the data voltage corresponding to the grayscale data to the pixel circuit. The pixel circuit 110 is formed in the pixel region defined by the data lines D1 to Dm and the scan lines S1 to Sn.

 The scan driver 200 sequentially applies a scan signal to the plurality of scan lines S1 to Sn.

The data driver 300 applies a data voltage to the plurality of data lines D1 to Dm.

The timing controller 400 receives the grayscale data signals R, G, and B data, the horizontal sync signal Hsync, and the vertical sync signal Vsync from an external or graphic controller (not shown), and controls necessary signals Sg and Sd. , Sb is transmitted to the scan driver 200, the data driver 300, and the light source controller 600, and the grayscale data R, G, and B DATA are transferred to the grayscale voltage generator 500.

The gray voltage generator 500 generates a data voltage having a magnitude corresponding to gray data and transmits the data voltage to the data driver 400.

The light source controller 600 controls the lighting timing of the light emitting diodes 800a, 800b, and 800c.

The light emitting diodes 700a, 700b, and 700c respectively output light corresponding to R, G, and B to the liquid crystal display panel 100. In the embodiment of the present invention, the light emitting diodes 700a, 700b, and 700c are used as the backlight, but the present invention is not limited thereto.

4 is a pixel circuit diagram of a liquid crystal display according to an exemplary embodiment of the present invention. In FIG. 4, only the pixel circuit connected to the j th data line Dj and the i th scan line Si is illustrated for convenience of description.

As shown in FIG. 4, the pixel circuit 110 according to the exemplary embodiment includes a TFT 10 and a liquid crystal capacitor C1.

The source electrode and the gate electrode of the TFT 10 are respectively connected to the data line Dj and the scan line Si, and apply the data voltage Vd supplied to the data line Dj to the pixel electrode (not shown). do.

The liquid crystal capacitor C1 is connected between the drain electrode of the TFT 10 and the common voltage Vcom, and thus the intensity of the electric field corresponding to the difference between the pixel voltage Vp and the common voltage Vcom applied to the liquid crystal capacitor C1. The light transmits at a transmittance corresponding to.

Next, an operation of the liquid crystal display according to the exemplary embodiment of the present invention will be described in detail with reference to FIG. 5.

5 is a driving timing diagram of a liquid crystal display according to an exemplary embodiment of the present invention.

As shown in FIG. 5, the liquid crystal display according to the exemplary embodiment of the present invention is driven by dividing one frame into an R field, a G field, and a B field. run with -filed). In FIG. 4, each field is divided into two subfields.

First, the scan signals are sequentially applied to the plurality of scan lines in the R1 subfield of the R field so that the TFT 10 is turned on. Then, the corresponding data voltage is applied to the data line and applied to the pixel electrode through the TFT 10. When the scan signal is applied to the last scan line of the R1 subfield, the scan signals are sequentially applied to the plurality of scan lines in the R2 subfield of the R field so that the TFT 10 is turned on. Then, the corresponding data voltage is applied to the data line and applied to the pixel electrode through the TFT 10.

Subsequently, a scan signal is sequentially applied to the plurality of scan lines in the G1 subfield of the G field, and the corresponding data voltage is applied to the pixel electrode through the TFT 10. Subsequently, a scan signal is sequentially applied to the plurality of scan lines in the G2 subfield, and the corresponding data voltage is applied to the TFT 10 to the pixel electrode. In this case, a data voltage having a polarity opposite to that of the R field is applied to the G field.

Next, when the G field ends, the scan signals are sequentially applied to the plurality of scan lines in the B1 subfield of the B field, and the corresponding data voltage is applied to the pixel electrode through the TFT 10. Subsequently, the scan signal is sequentially applied to the plurality of scan lines in the B2 subfield, and the corresponding data voltage is applied to the TFT 10 to the pixel electrode. In this case, a data voltage having a polarity opposite to that of the G field is applied to the B field.

In this way, by sequentially displaying the images corresponding to the R, G, and B color components in the R, G, and B fields, the images of the R, G, and B color components are synthesized by human visual afterimage. The color image for one frame is displayed.

In general, the liquid crystal of the liquid crystal display device has a characteristic that the molecular arrangement of the liquid crystal is changed along the direction of the electric field when a voltage is applied. Accordingly, the liquid crystal display displays an image by using the property of the liquid crystal. When the data voltage of the same polarity is continuously applied, as shown in FIG. 1, the image quality is deteriorated because an electric field is formed in one direction and the liquid crystal deteriorates. The lifetime of the liquid crystal is shortened. Therefore, in the exemplary embodiment of the present invention, deterioration of the liquid crystal is prevented by applying a data voltage having an inverted polarity for each field.

FIG. 6 is a diagram illustrating a voltage applied to a liquid crystal in a pixel region defined by an i th scan line Si and a j th data line Dj during one frame.

As shown in FIG. 6, when the data voltage for expressing the gray scale is applied to the liquid crystal capacitor C1 in one field, and then the same data voltage is applied again, more accurate gray scale can be expressed. Will be.

In the embodiment of the present invention, the same data voltage having the same polarity is applied twice in one field, but may be applied more than once.

Although the preferred embodiment of the present invention has been described in detail above, the scope of the present invention is not limited thereto, and various modifications and variations are possible. For example, the present invention can be applied to not only a field sequential liquid crystal display but also a color filter liquid crystal display. In this case, in the color filter type liquid crystal display, one frame may be divided into a plurality of subfields, and a plurality of identical data voltages may be applied and driven in one frame as described above.

According to the present invention, more accurate gradation is expressed by applying the same voltage of the same polarity two or more times in one field.

Claims (7)

A driving method of a liquid crystal display device comprising a plurality of data lines for transmitting a data voltage representing an image, a plurality of scanning lines for transmitting a scanning signal, and a plurality of pixels defined by the data lines and the scanning lines. A frame is sequentially driven to a first field, a second field, and a third field to which the first light, the second light, and the third light are respectively applied, wherein each field of the first to third fields is the first and second fields. Divided into a plurality of subfields including sub-fileds, In each of the first to third fields, Applying a first scan signal to the plurality of scan lines in the first subfield, and applying a first data voltage to the data line in response to the first scan signal; and Applying a second scan signal to the plurality of scan lines in the second subfield, and applying a second data voltage having the same polarity as the first data voltage to the data line in response to the second scan signal; Including; And a polarity of the first and second data voltages is inverted for each field of the first to third fields. The method of claim 1, And the first data voltage and the second data voltage are the same data voltage. delete The method according to claim 1 or 2, And the first, second and third lights are red, green and blue, respectively. A driving method of a liquid crystal display device comprising a plurality of data lines for transmitting a data voltage representing an image, a plurality of scanning lines for transmitting a scanning signal, and a plurality of pixels defined by the data lines and the scanning lines. A frame is divided into a plurality of fields, at least one of the plurality of fields is driven by being divided into a plurality of subfields including first and second sub-fields, The at least one field is Sequentially applying a first scan signal to the plurality of scan lines in the first subfield, and applying a first data voltage to the data line in response to the first scan signal; and Sequentially applying a second scan signal to the plurality of scan lines in the second subfield, and applying a second data voltage having the same polarity as the first data voltage to the data line in response to the second scan signal. Including; And a polarity of the first and second data voltages is inverted for each frame. The method of claim 5, And the first data voltage and the second data voltage are the same data voltage. delete

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