KR20040070542A - reflective or transflective liquid crystal display device and operating method the same - Google Patents

Abstract

PURPOSE: An LCD(Liquid Crystal Display) having a reflection mode and a method for driving the LCD are provided to control luminance and color reproducibility in response to external environments. CONSTITUTION: An LCD includes red pixels(R), green pixels(G), blue pixels(B) and white pixels(W). The LCD controls the quantity of lights transmitting the white pixels in response to brightness of surrounding lights. When the brightness of surrounding lights is high, the lights transmitting the white pixels are shielded. When the brightness of surrounding lights is low, the quantity of the lights transmitting the white pixels is increased. The red, green, blue and white pixels have the same area. The transmissivity of each of the red, green and blue pixels is 0.25 to 0.35, and aperture ratio is 0.60 to 0.75.

Description

Liquid crystal display and driving method including reflective mode {reflective or transflective liquid crystal display device and operating method the same}

The present invention relates to a liquid crystal display device, and more particularly, to a liquid crystal display device including a reflection mode and a driving method thereof.

With the recent rapid development of the information society, a flat panel display with excellent characteristics such as thinning, light weight, and low power consumption has been developed, replacing the existing cathode ray tube (CRT) and replacing the display device. It forms the mainstream of display devices.

Flat panel display devices can be classified according to whether they have self-luminous ability or not. A light emitting display device displays an image by emitting light by itself, and there is no light emitting element to display an image using an external light source. This is called a light receiving display device.

The light emitting display includes a plasma display panel, a field emission display, an electroluminescence display, and the like. A light receiving display includes a liquid crystal display. Crystal displays are the most representative ones, and they are actively applied to laptop computers such as laptops and desktop monitors because of their excellent resolution, color display, and image quality.

The liquid crystal display device includes a liquid crystal display panel which displays an image viewed from the outside as the most essential part, which includes two substrates having electric field generating electrodes formed on each surface thereof. They are arranged to face each other and have a structure in which a liquid crystal material is interposed therebetween.

As is well known, liquid crystals have a thin and long molecular structure and have dielectric anisotropy and refractive anisotropy. Accordingly, the liquid crystal panel may arbitrarily adjust the arrangement direction of the liquid crystal molecules interposed therebetween by adjusting a voltage difference between two opposing field generating electrodes, and change transmittance according to polarization characteristics of light.

However, since the liquid crystal panel is a light receiving device that does not have a self-luminous element, a separate light source is required, and a light is incident to the liquid crystal panel by arranging a backlight on the rear of the liquid crystal panel. Various images can be displayed by adjusting the amount of permeation.

In this case, the two opposing field generating electrodes of the liquid crystal display should be made of a transparent conductive material, and the two substrates are also made of a transparent substrate.

The liquid crystal display device described above is called a transmission type liquid crystal display device. Since an artificial back light source such as a backlight is used, the liquid crystal display device has an advantage of realizing a bright image even in a dark external environment, but consumes power due to the backlight. ) Has a big disadvantage.

In order to compensate for this, a reflection type liquid crystal display device has been proposed.

The reflective liquid crystal display device uses ambient light such as natural light or artificial light instead of a separate light source such as a backlight, and has an advantage of lower power consumption than a transmissive liquid crystal display device.

Hereinafter, a general reflective liquid crystal display device will be described with reference to the accompanying drawings.

FIG. 1 is an exploded perspective view of a liquid crystal panel 1 for a general reflective liquid crystal display device, and FIG. 2 is a cross-sectional view taken along the line II-II thereof.

In the liquid crystal panel 1 of the general reflective liquid crystal display device, the first and second substrates 2 and 4 face each other with a predetermined distance therebetween with the liquid crystal 6 interposed therebetween.

The lower first substrate 2 is formed with a first insulating substrate 10 and a plurality of gate lines 11 made of a conductive material such as metal and a gate electrode 12 branched therefrom. A gate insulating film 14 made of a silicon nitride film (SiN _x ) or a silicon oxide film (SiO ₂ ) covers the entire surface.

An active layer 16 made of amorphous silicon is formed on the gate insulating layer 14 on the gate electrode 12, and an ohmic contact layer 18 made of amorphous silicon doped with impurities is formed thereon. In addition, a data line 20 made of a conductive material such as a metal and intersecting the gate line 11, a source electrode 22 branching therefrom and positioned above the ohmic contact layer 18, and the source electrode 22. Drain electrodes 24 spaced apart from each other are formed to form a thin film transistor (T).

Subsequently, a passivation layer 26 made of a silicon nitride layer, a silicon oxide layer, or an organic insulating layer is formed on the source and drain electrodes 22 and 24, and the passivation layer 26 forms a contact hole 26a exposing the drain electrode 24. Have

A pixel electrode 28 made of an opaque conductive material such as metal is formed in the pixel region P on the passivation layer 26, and the pixel electrode 28 is connected to the drain electrode 24 through the contact hole 26a. )

On the other hand, the second substrate 4 is formed of a black matrix 32 as the second insulating substrate 30 and a lower surface thereof, which covers the edge of the pixel electrode 28 and is formed at a portion other than the pixel electrode 28. Prevent light leaks In addition, the black matrix 32 is formed at a position corresponding to the thin film transistor T, thereby preventing light from entering the channel of the thin film transistor T, thereby preventing photo current generation.

A color filter layer 34 is formed below the black matrix 32. The color filter layer 34 has red, green, and blue (R), green (G), and blue (B) colors, respectively. It consists of a repetitive arrangement of the filters 34a, 34b, 34c. In this case, the red, green, and blue color filters 34a, 34b, and 34c correspond one-to-one with the pixel electrode 28, respectively, and the three colors of red, green, and blue form one pixel. Therefore, the red, green, and auditory color filters form a sub-pixel.

The common electrode 36 made of a transparent conductive material is formed under the color filter layer 34.

Next, the liquid crystal layer 6 is positioned between the pixel electrode 28 and the common electrode 36.

In particular, the reflective liquid crystal display device described above uses a material such as a metal which is well reflected as the pixel electrode 28, and the light incident from the outside passes through the second substrate 4 and the liquid crystal layer 6, and thus the pixel. After reflecting by the electrode 28, it penetrates the liquid crystal layer 6 and the 2nd board | substrate 4 again, and goes out. Therefore, a separate light source can be omitted, thereby reducing power consumption.

However, in the reflection type liquid crystal display device, since the external light passes through the color filter layer 34 twice, the light efficiency remains at about 24%, which is much lower than that of the transmissive liquid crystal display device.

Since the light efficiency is composed of the product of the transmittance and the aperture ratio of the color filter, the color filter layer 34 may be reduced in thickness to increase the light efficiency by about 32%, but in this case, the color filter layer 34 becomes thinner, so the color purity is increased. Falling color shows a drawback of decreasing color reproducibility.

The present invention has been made to solve the above problems, an object of the present invention is to provide a method of driving a liquid crystal display device including a reflection mode that can adjust the brightness and color reproduction characteristics in accordance with the external environment in an optimal state will be.

1 is an exploded perspective view of a typical reflective liquid crystal display device

2 is a cross-sectional view taken along the line II-II of FIG.

3 is an exploded perspective view of a reflective liquid crystal display device according to the present invention;

4 is a cross-sectional view taken along the line IV-IV of FIG. 3.

5 is a chromaticity diagram by a CIE colorimetric system

6 is a block diagram of a liquid crystal panel and a circuit unit of the reflective liquid crystal display device according to the present invention.

7 is an exploded perspective view of a transflective liquid crystal display device according to the present invention;

<Description of the symbols for the main parts of the drawings>

101 liquid crystal panel 102 first substrate

104: second substrate 106: liquid crystal

110: first insulating substrate 111: gate line

120: data line 128: pixel electrode

130: second insulating substrate 132: black matrix

134: color filter layer 134a, 134b, 134c, 134d: red, green, blue, white color filter

136: common electrode T: thin film transistor

P: Pixel area R, G, B, W: Red, Green, Blue, White Subpixel

In order to achieve the above object, the present invention provides a liquid crystal display including a red subpixel, a green subpixel, a blue subpixel, and a white subpixel without color. Provided is a liquid crystal display device which controls the amount of light passing through a pixel. In this case, when the ambient light is bright, the light passing through the white subpixel is blocked, and when the ambient light is dark, the amount of light transmitted through the white subpixel is increased. In addition, the liquid crystal display is characterized in that the reflective or transflective type. In addition, the red, green, blue, and white subpixels each have substantially the same area, and the transmittance of the red, green, and blue subpixels is 0.25 to 0.35, respectively, and the aperture ratio is 0.60 to 0.75.

In addition, the present invention and the first substrate; A plurality of gate lines and data lines crossing each other on an upper surface of the first substrate to define pixel regions; A thin film transistor formed at an intersection point of the gate line and the data line; A pixel electrode connected to the thin film transistor and positioned in each pixel region; A second substrate facing the first substrate; A black matrix formed on the lower surface of the second substrate; A color filter layer corresponding to each pixel area below the black matrix, the color filter layer including a red color filter, a green green color filter, a blue blue color filter, and a repetitive arrangement of a white color filter having no color; A common electrode formed under the color filter layer; A liquid crystal display device including a liquid crystal interposed between the pixel electrode and the common electrode and controlling the amount of light passing through the white subpixel according to the brightness of ambient light is provided. In this case, when the ambient light is bright, the light passing through the back color filter is blocked, and when the ambient light is dark, the amount of light passing through the back color filter is increased. The pixel electrode is a reflective liquid crystal display device made of an opaque metal material, or the pixel electrode is divided into a transparent part made of a transparent conductive material and a reflective part made of an opaque conductive material. The pixel electrode is disposed under the first substrate. It is a semi-transmissive liquid crystal display device further comprising a backlight for emitting light toward one substrate. In addition, the red, green, blue, and white color filters have substantially the same area, respectively, the transmittance of the red, green, blue color filter is 0.25 to 0.35, characterized in that the aperture ratio is 0.60 to 0.70.

The present invention also includes a liquid crystal panel comprising a plurality of gate lines and data lines crossing each other to define respective pixel regions, and red, green, blue, and white subpixels formed corresponding to the pixel regions; An interface which is externally input and receives an image signal source including an RGB signal; A data signal changing unit which converts the RGB signal into an RGBW signal; A timing controller generating a gate control signal and a data control signal through an image signal source including the RGBW signal; A gamma power supply unit which selects an image signal through the RGBW signal; A data driver configured to transmit the data control signal and the image signal and to connect one end of the plurality of data lines; The gate control signal is transmitted and includes a gate driver connecting one end of the plurality of gate lines to provide a liquid crystal display device for controlling the amount of light passing through the white subpixel according to the brightness of ambient light. In this case, the data signal changing unit lowers the brightness of the W signal when the ambient light is bright, and increases the brightness of the W signal when the ambient light is dark.

In another aspect, the present invention provides a method of driving a liquid crystal display device comprising a red subpixel, a green subpixel, a blue subpixel, and a white subpixel having no color, which transmits the white subpixel when the ambient light is bright. The present invention provides a method of driving a liquid crystal display device that blocks light and increases the amount of light transmitted through the white subpixel when the ambient light is dark. At this time, the liquid crystal display is characterized in that the reflective or transflective type. In addition, the red, green, blue, and white subpixels each have substantially the same area, and the transmittance of the red, green, and blue subpixels is 0.25 to 0.35, respectively, and the aperture ratio is 0.60 to 0.75. With reference to the accompanying drawings, it will be described in detail an embodiment of the present invention.

3 is an exploded perspective view of a reflective liquid crystal display device, in particular, a liquid crystal panel 101, and FIG. 4 is a cross-sectional view taken along the line IV-IV of FIG. 3.

Referring to these, the reflective liquid crystal display device 101 according to the present invention has a structure in which the first and second substrates 102 and 104 are arranged to face each other, and the liquid crystal 106 is interposed therebetween.

First, the lower first substrate 102 has a first insulating substrate 110, and a gate line 111 and a data line 120 vertically and horizontally define a pixel region P, and each pixel region P In this case, the thin film transistor T and the pixel electrode 128 are arranged.

In more detail, a gate line 111 made of a conductive material such as a metal and a gate electrode 112 branched therefrom are formed on the first insulating substrate 110, and a gate insulating film made of a silicon nitride film or a silicon oxide film is formed thereon. 114 is covered on the front of the substrate. An island-like active layer 116 made of amorphous silicon is formed on the gate insulating layer 114 on the gate electrode 112, and an ohmic contact layer 118 made of amorphous silicon doped with impurities is formed thereon. have. In addition, the ohmic contact layer 118 may include a data line 120 made of a conductive material such as a metal, a source electrode 122 branched therefrom, and a drain electrode 124 spaced apart from the source electrode 122. ) Is formed to form a thin film transistor (T).

A protective film 126 made of a silicon nitride film, a silicon oxide film, or an organic insulating film is formed thereon, and the protective film 126 has a contact hole 126a exposing the drain electrode 124.

In the pixel region P above the passivation layer 126, a pixel electrode 128 made of an opaque conductive material such as metal is formed in each pixel, and the pixel electrode 128 is formed through the contact hole 126a. It is connected to the drain electrode 124.

The second substrate 104 facing each other with the first substrate 102 and the liquid crystal 106 interposed therebetween has a second insulating substrate 130 and a black matrix 132 formed thereunder. The black matrix 132 covers the edges of the pixel electrodes 128 of the first substrate 102 to prevent light leakage from portions other than the pixel electrodes 128 and to fill in the gaps between the color filters described below. Have In addition, the black matrix 132 is formed at a position corresponding to the thin film transistor T to prevent photocurrent generation.

The color filter layer 134 is formed under the black matrix 132. In particular, the color filter layer 134 according to the present invention has substantially the same area, and has red, green, and green colors corresponding to each pixel area P. FIG. It is characterized by consisting of a repeating arrangement of blue and white color filters (134a, 134b, 134c, 134d).

In this case, the red, green, and blue color filters 134a, 134b, and 134c have red, green, and blue colors, respectively, and the back color filter 134d does not have color. In particular, the back color filter 134d is made of a separate material. Rather, it may consist of a thicker overcoat layer or a buffer layer of a transparent insulating material to compensate for the steps of other red, green, and blue color filters (134a, 134b, 134c).

This back color filter 134d will be used in a consistent sense herein below.

Therefore, the three colors of red, green, blue, and white form one pixel. In the reflective LCD according to the present invention, the red, green, blue, and white color filters 134a, 134b, 134c, 134d) forms red, green, blue, and white subpixels (R, G, B, and W), respectively.

A common electrode 136 made of a transparent conductive material is formed under the color filter layer 134.

The liquid crystal panel for the reflective liquid crystal display according to the present invention is characterized by the subpixels R, G, and B composed of red, green, blue, and white color filters 134a, 134b, and 134c corresponding to each pixel area P. FIG. When the ambient light is bright, in particular, the white sub-pixel (W) does not output light, whereas when the ambient light is dark, red, green, blue sub-pixel (R, G, B) In addition to the light from the white sub-pixel (W) is characterized in that the output.

That is, the reflective LCD according to the present invention includes a white sub-pixel W whose light transmittance is adjusted according to the brightness of the ambient light. When the ambient light is strong, the liquid crystal array corresponding to the pixel area P is strong. By controlling the condition, light emitted through the white subpixels (W) is blocked. Therefore, the amount of light incident into the liquid crystal panel 101 is increased than usual, but since the light is output through only the color filters 134a, 134b, and 134c of red, green, and blue which have good color reproducibility, an image with improved color reproducibility is obtained. Can be.

On the other hand, when the ambient light is weak, the brightness of the light output through the white subpixel W is controlled by adjusting the liquid crystal array state corresponding to the pixel area P. In this case, the gray value of the white subpixel W may be determined according to the gray values of red, green, and blue subpixels R, G, and B, and the gray value of the gray of the white subpixel W is gray. Although color purity may be reduced due to the component, the color reproducibility may be somewhat reduced, but the light efficiency is improved by the light transmittance in the white subpixel W.

In particular, considering that the brightness of the image is more important than the color characteristics because the ambient light is dark, a more improved image can be obtained.

In general, the color reproduction range can be expressed as a chromaticity diagram by a CIE colorimeter, which is based on the measured values by the spectrophotometer. All the colors are represented by the mixing ratio of the amount stimulating the optic nerve) and Z (the amount stimulating the optic nerve that feels blue).

It is expressed by the integral of the product of the spectrum of light from the backlight, the spectrum of light passing through the color filter, and the color matching function.

Therefore, the tristimulus value

Φ (λ) is the spectrum of the object to be measured and represents the spectral wavelength distribution energy of the light source.

The ratio of the three stimulus values is defined as chromaticity coordinates. The chromaticity coordinate values x, y, and z satisfy the relationship of x + y + z = 1,

It is expressed as

By using this, all colors can be represented by three values of x, y, and Y. Here, Y is a luminance value, x and y represent chromaticity as a set, and it is the property of the color except brightness.

The chromaticity diagram by the CIE color system is shown in FIG. 5, where all the colors can be represented by a point inside the saddle shape.

Here, the areas denoted by reference numerals A and B indicate the color reproduction range of the image represented by the reflective liquid crystal display device according to the present invention when the external light is bright and dark, respectively. When the light is bright, that is, when the light passing through the white subpixel (W: see FIG. 3) is blocked, the area B inside thereof is dark when the ambient light is dark, that is, the white subpixel (W: see FIG. 3). Indicates the transmission of light.

In this case, preferably, in the reflective LCD according to the present invention, the transmittances of the color filters 134a, 134b, and 134c of the red, green, and blue subpixels R, G, and B are about 0.3, respectively. It is preferable that the aperture ratio is about 0.65. Therefore, since the transmittance of the white subpixel is about 1, the light efficiency may be about 31%.

Meanwhile, the circuit structure of the reflective liquid crystal display according to the present invention is shown in FIG. 6, which is a block diagram showing the liquid crystal panel 101 and the circuit unit connected to the reflective liquid crystal display.

As illustrated, the liquid crystal panel 101 includes a plurality of gate lines 111 and data lines 120 that cross each other to define the pixel region P. Referring to FIG.

The circuit unit includes an interface 210, a data signal changer 220, a timing controller 230, a gamma power supply 240, a gate driver 250, and a data driver 260.

Here, the interface 210 is a portion in which a video signal source is initially transmitted from the outside, and the video signal source includes various clock signals and RGB signals.

Next, the data signal changing unit 220 converts the input RGB signal into an RGBW signal, and the RGBW signal is adjusted according to external light as mentioned above.

Next, the timing controller 230 generates a timing-synchronized gate control signal and a data control signal through the various clock signals and the RGBW signal, and the gate control signal is the gate driver 250, and the data control signal is the data. Output to the driver 260.

Next, the gamma power supply unit 240 appropriately selects an image signal to be transmitted to each pixel region P through the RGBW signal and transmits the image signal to the data driver 260.

In this case, the gate driver 250 is positioned at one edge of the liquid crystal panel 101 to connect one end of the plurality of gate lines 111, and scans the gate signal for each frame into the plurality of gate lines 111 through the gate control signal. (scan) pass.

On the other hand, the data driver 260 is located at the other side edge of the liquid crystal panel 101 adjacent to the gate driver 250 to connect one end of the plurality of data lines 120, and corresponds to each gate signal through the data control signal and the image signal. The data signal is transmitted to the plurality of data lines 120.

In the reflective liquid crystal display according to the present invention, the data driver 260 is increased by 1/3.

On the other hand, the reflective liquid crystal display device according to the present invention can be applied to a transflective liquid crystal display device, the transflective liquid crystal display device refers to a liquid crystal display device that can be used in the reflection mode and the transmission mode.

FIG. 7 is an exploded perspective view of a liquid crystal panel for a transflective liquid crystal display according to the present invention. In this case, the structure of the liquid crystal panel for a transflective liquid crystal display according to the present invention is mostly similar to the reflective liquid crystal display as described above. The same reference numerals are given to the same parts, and duplicate description thereof will be omitted.

In the case of the transflective liquid crystal display device according to the present invention, a backlight is provided on the rear surface of the liquid crystal panel 101. In particular, the pixel electrode 128 includes a transparent part of the transparent material 300a and a transparent part of the transparent material 300b The light transmitting unit 300a allows the light emitted from the backlight to pass through, and the reflecting unit 300b blocks the light emitted from the backlight, but may reflect external ambient light.

In addition, the transflective liquid crystal panel 101 also includes red, green, blue, and white color filters 134a, 134b, 134c, and 134d corresponding to each pixel area P. It forms a white subpixel (R, G, B, W). Therefore, when the ambient light is bright, the light passing through the white subpixel W is blocked to pass only the color filters 134a, 134b, and 134c of red, green, and blue which have good color reproducibility. The light efficiency can be improved by allowing light to pass through the white subpixel (W).

The present invention provides a liquid crystal display device including a white subpixel whose transmittance of light is adjusted according to ambient light, and a method of driving the same. A color reproduction characteristic and a color transmittance may be determined by determining a maximum transmittance of a white subpixel according to ambient light intensity. It has the advantage of optimizing the light efficiency.

The present invention is particularly effective when applied to a reflective or transflective type. When the ambient light is bright, color reproduction close to the transmissive liquid crystal display device is possible. On the contrary, when the ambient light is dark, the conventional reflection is performed. The luminance close to the mold can be obtained, and thus an improved image can be obtained.

Claims (14)

A liquid crystal display device comprising a red subpixel, a green subpixel, a blue subpixel, and a white subpixel having no color. A liquid crystal display for adjusting the amount of light passing through the white subpixel according to the brightness of the ambient light The method according to claim 1, A liquid crystal display device that blocks the light passing through the white subpixel when the ambient light is bright and increases the amount of light transmitted through the white subpixel when the ambient light is dark. The method according to claim 1, The liquid crystal display device is characterized in that the reflection type or transflective liquid crystal display device The method according to claim 1, The red, green, blue, and white subpixels have substantially the same area, and the transmittance of the red, green, and blue subpixels is 0.25 to 0.35, respectively, and the aperture ratio is 0.60 to 0.75. A first substrate; A plurality of gate lines and data lines crossing each other on an upper surface of the first substrate to define pixel regions; A thin film transistor formed at an intersection point of the gate line and the data line; A pixel electrode connected to the thin film transistor and positioned in each pixel region; A second substrate facing the first substrate; A black matrix formed on the lower surface of the second substrate; A color filter layer corresponding to each pixel area below the black matrix, the color filter layer including a red color filter, a green green color filter, a blue blue color filter, and a repetitive arrangement of a white color filter having no color; A common electrode formed under the color filter layer; Including a liquid crystal interposed between the pixel electrode and the common electrode, A liquid crystal display for adjusting the amount of light passing through the white subpixel according to the brightness of the ambient light The method according to claim 5, A liquid crystal display for blocking the light passing through the back color filter when the ambient light is bright, and increasing the amount of light passing through the back color filter when the ambient light is dark The method according to claim 5, The pixel electrode is a reflective liquid crystal display device made of an opaque metal material. The method according to claim 5, The pixel electrode is divided into a transmission part made of a transparent conductive material and a reflection part made of an opaque conductive material. A backlight disposed under the first substrate to emit light toward the first substrate Liquid crystal display device comprising a transflective liquid crystal display device further comprising The method according to claim 5, The red, green, blue, and white color filters have substantially the same area, and the transmittances of the red, green, and blue color filters are respectively 0.25 to 0.35, and the aperture ratio is 0.60 to 0.70. A liquid crystal panel including a plurality of gate lines and data lines crossing each other to define each pixel area, and red, green, blue, and white subpixels formed corresponding to each pixel area; An interface which is externally input and receives an image signal source including an RGB signal; A data signal changing unit which converts the RGB signal into an RGBW signal; A timing controller generating a gate control signal and a data control signal through an image signal source including the RGBW signal; A gamma power supply unit which selects an image signal through the RGBW signal; A data driver configured to transmit the data control signal and the image signal and to connect one end of the plurality of data lines; A gate driver for transmitting the gate control signal and connecting one end of the plurality of gate lines; Including, the liquid crystal display for adjusting the amount of light passing through the white sub-pixel according to the brightness of the ambient light The method according to claim 10, The data signal changing unit lowers the brightness of the W signal when the ambient light is bright, and increases the brightness of the W signal when the ambient light is dark. A driving method of a liquid crystal display device comprising a red subpixel, a green subpixel, a blue subpixel, and a white subpixel having no color. A method of driving a liquid crystal display device that blocks light passing through the white subpixel when the ambient light is bright and increases the amount of light transmitted through the white subpixel when the ambient light is dark. The method according to claim 12, The liquid crystal display device is a method of driving a liquid crystal display device, characterized in that the reflective or transflective type The method according to claim 12, The red, green, blue, and white subpixels have substantially the same area, and the transmittance of the red, green, and blue subpixels is 0.25 to 0.35, respectively, and the aperture ratio is 0.60 to 0.75.