KR102513678B1 - Liquid crystal display and method for driving the same - Google Patents

Abstract

Embodiments of the present invention relate to a liquid crystal display capable of preventing deterioration of image quality when implementing local dimming when an edge type backlight unit is used, and a method for driving the same. A liquid crystal display device according to an embodiment of the present invention includes a liquid crystal display panel including a plurality of pixels and a plurality of light sources to radiate light to the rear surface of the liquid crystal display panel, based on the dimming value of each of the local dimming blocks. A backlight unit that drives light sources for each local dimming block, a backlight control unit that analyzes digital video data for each local dimming block and determines a dimming value for each local dimming block, and is disposed between the liquid crystal display panel and the backlight unit and transmits light from the backlight unit for each transmittance control block. It includes a transmittance variable panel for adjusting the transmittance of light incident on the liquid crystal display panel, and a transmittance variable controller for determining the light transmittance for each transmittance control block by analyzing digital video data for each transmittance control block.

Description

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

The present invention relates to a liquid crystal display device and a driving method thereof.

A liquid crystal display of an active matrix driving method displays an image using a thin film transistor (hereinafter referred to as "TFT") as a switching element. Liquid crystal display devices can be miniaturized compared to cathode ray tubes (Cathode Ray Tubes, CRT), so they are applied not only to displays in portable information devices, office equipment, computers, etc., but also to televisions, rapidly replacing cathode ray tubes.

A liquid crystal display device displays an image by modulating light incident from a backlight unit by controlling an electric field applied to a liquid crystal layer. An image quality of a liquid crystal display device is greatly influenced by a contrast ratio. However, there is a limit to improving the contrast ratio only by modulating the light transmittance of the liquid crystal layer by controlling the data voltage applied to the liquid crystal layer.

In order to improve the contrast ratio of a liquid crystal display device, a backlight dimming method of adjusting the luminance of a backlight unit according to an image has been proposed. Backlight dimming methods include a global dimming method in which the luminance of the display surface is entirely adjusted, and a local dimming method in which the luminance of the display surface is partially adjusted. The global dimming method can improve dynamic contrast ratio. The local dimming method can improve a static contrast ratio, which is difficult to improve with the global dimming method, by partially controlling the luminance of the display surface within one frame period.

The liquid crystal display device can be divided into a direct type liquid crystal display device in which light sources are disposed on the rear surface of the liquid crystal display panel and an edge type liquid crystal display device in which light sources are disposed on the side surface of the liquid crystal display panel. The edge-type liquid crystal display can reduce the thickness compared to the direct-type liquid crystal display, but it is difficult to realize perfect local dimming because the light sources are arranged only on the side of the liquid crystal display panel. If local dimming is not properly implemented, there is a problem in that picture quality is deteriorated.

Embodiments of the present invention provide a liquid crystal display device capable of preventing deterioration of image quality when implementing local dimming when an edge type backlight unit is used, and a method for driving the same.

A liquid crystal display device according to an embodiment of the present invention includes a liquid crystal display panel including a plurality of pixels and a plurality of light sources to radiate light to the rear surface of the liquid crystal display panel, based on the dimming value of each of the local dimming blocks. A backlight unit that drives light sources for each local dimming block, a backlight control unit that analyzes digital video data for each local dimming block and determines a dimming value for each local dimming block, and is disposed between the liquid crystal display panel and the backlight unit and transmits light from the backlight unit for each transmittance control block. It includes a transmittance variable panel for adjusting the transmittance of light incident on the liquid crystal display panel, and a transmittance variable controller for determining the light transmittance for each transmittance control block by analyzing digital video data for each transmittance control block.

A method of driving a liquid crystal display according to an embodiment of the present invention includes determining a dimming value for each local dimming block by analyzing digital video data for each local dimming block, and determining a dimming value for each local dimming block for backlight for each local dimming block. Driving the light sources of the unit, determining the light transmittance for each transmittance control block by analyzing the digital video data for each transmittance control block, and transmittance of light input from the backlight unit for each transmittance control block according to the light transmittance determined for each transmittance control block. includes adjusting the

According to an exemplary embodiment of the present invention, transmittance of a variable transmittance block that does not need to be provided with high luminance light to display a dark image may be lowered. As a result, since the embodiment of the present invention properly implements local dimming even in the case of an edge type backlight unit, it is possible to prevent deterioration of image quality due to local dimming.

Further, in an embodiment of the present invention, the transmittance of light incident from the backlight unit to the liquid crystal display panel can be controlled by disposing the variable transmittance panel between the liquid crystal display panel and the backlight unit. That is, in an embodiment of the present invention, since local dimming can be performed using a variable transmittance panel as well as a backlight unit, a static contrast ratio can be further increased.

In addition, the embodiment of the present invention can be simply designed without including a thin film transistor by setting the region where the first electrode and the second electrode of the variable transmittance panel overlap each other as a transmittance control block. Due to this, the embodiment of the present invention can reduce the manufacturing cost of the variable transmittance panel.

In addition, in an embodiment of the present invention, the size of the transmittance control block of the variable transmittance panel may be set to be larger than the size of the pixel. Due to this, since the embodiment of the present invention does not require precise alignment when attaching the liquid crystal display and the variable transmittance panel, manufacturing cost can be further reduced.

Furthermore, in an embodiment of the present invention, since the variable transmittance panel does not include a thin film transistor, formation of opaque metal lines on the variable transmittance panel can be minimized. It is possible to prevent moiré from occurring due to light interference caused by reflection or refraction in opaque metal lines of .

1 is a block diagram showing a liquid crystal display according to an exemplary embodiment of the present invention.
FIG. 2 is an exemplary diagram showing a pixel of FIG. 1 .
FIG. 3 is a cross-sectional view showing the liquid crystal display panel, the backlight unit, and the variable transmittance panel of FIG. 1 .
4 is a cross-sectional view showing an example of the variable transmittance panel of FIG. 3 .
5 is a cross-sectional view showing another example of the variable transmittance panel of FIG. 3 .
6 is a cross-sectional view showing another example of the variable transmittance panel of FIG. 3 .
7 is a cross-sectional view showing another example of the variable transmittance panel of FIG. 3 .
8 is a plan view illustrating an example of a first electrode and a second electrode of a variable transmittance panel.
9 is a plan view showing another example of the first electrode and the second electrode of the variable transmittance panel.
10A and 10B are exemplary views illustrating a local dimming block of a backlight unit and a transmittance control block of a variable transmittance panel.
11A and 11B are exemplary views showing an example of an output image when only backlight dimming is applied according to an input image and an example of an output image when both backlight dimming and transmittance variation are applied according to an input image.
12 is a flowchart illustrating a method of driving a liquid crystal display device according to an exemplary embodiment of the present invention.

Advantages and features of the present invention, and methods of achieving them, will become clear with reference to the detailed description of the following embodiments taken in conjunction with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but will be implemented in various different forms, only these embodiments make the disclosure of the present invention complete, and common knowledge in the art to which the present invention belongs. It is provided to fully inform the holder of the scope of the invention, and the present invention is only defined by the scope of the claims.

The shapes, sizes, ratios, angles, numbers, etc. disclosed in the drawings for explaining the embodiments of the present invention are illustrative, so the present invention is not limited to the details shown. Like reference numbers designate like elements throughout the specification. In addition, in describing the present invention, if it is determined that a detailed description of related known technologies may unnecessarily obscure the subject matter of the present invention, the detailed description will be omitted.

When 'includes', 'has', 'consists', etc. mentioned in this specification is used, other parts may be added unless 'only' is used. In the case where a component is expressed in the singular, the case including the plural is included unless otherwise explicitly stated.

In interpreting the components, even if there is no separate explicit description, it is interpreted as including the error range.

In the case of a description of a positional relationship, for example, 'on top of', 'on top of', 'at the bottom of', 'next to', etc. Or, unless 'directly' is used, one or more other parts may be located between the two parts.

In the case of a description of a temporal relationship, for example, 'immediately' or 'directly' when a temporal precedence relationship is described in terms of 'after', 'following', 'next to', 'before', etc. It can also include non-continuous cases unless is used.

Although first, second, etc. are used to describe various components, these components are not limited by these terms. These terms are only used to distinguish one component from another. Therefore, the first component mentioned below may also be the second component within the technical spirit of the present invention.

"X-axis direction", "Y-axis direction", and "Z-axis direction" should not be interpreted only as a geometric relationship in which the relationship between each other is made upright, and may be broader within the range in which the configuration of the present invention can function functionally. It can mean having a direction.

The term “at least one” should be understood to include all possible combinations from one or more related items. For example, "at least one of the first item, the second item, and the third item" means not only the first item, the second item, or the third item, respectively, but also two of the first item, the second item, and the third item. It may mean a combination of all items that can be presented from one or more.

Each feature of the various embodiments of the present invention can be partially or entirely combined or combined with each other, technically various interlocking and driving are possible, and each embodiment can be implemented independently of each other or can be implemented together in a related relationship. may be

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a block diagram showing a liquid crystal display according to an exemplary embodiment of the present invention. Referring to FIG. 1 , a liquid crystal display device according to an embodiment of the present invention includes a liquid crystal display panel 100, a backlight unit 200, a variable transmittance panel 300, a data driver 110, a gate driver 120, It includes a timing controller 130, a backlight driver 140, and a variable transmittance panel driver 150.

The liquid crystal display panel 100 includes an upper substrate 101, a lower substrate 102, and a liquid crystal layer LC interposed therebetween. On the lower substrate of the liquid crystal display panel 100, data lines D1 to Dm and gate lines G1 to Gn are disposed to cross each other. Pixels P are arranged in a matrix form on the liquid crystal display panel 100 by the cross structure of the data lines D1 to Dm and the gate lines G1 to Gn. Each of the pixels P may be connected to one of the data lines D1 to Dm and one of the gate lines G1 to Gn. Accordingly, the pixel P receives the data voltage of the data line when the gate signal is supplied to the gate line, and emits light with a predetermined brightness according to the supplied data voltage.

For example, each of the pixels P may include a transistor T, a pixel electrode PE, a common electrode CE, and a storage capacitor Cst, as shown in FIG. 2 . The transistor T may be a thin film transistor formed by a semiconductor process. The transistor T responds to the gate signal of the kth (k is a positive integer satisfying 1≤k≤n) gate line Gk (j is a positive integer satisfying 1≤j≤m). The data voltage of the data line Dj is supplied to the pixel electrode PE. Accordingly, each of the pixels P drives the liquid crystal of the liquid crystal layer LC by an electric field generated by a potential difference between the data voltage supplied to the pixel electrode PE and the common voltage supplied to the common electrode CE. A transmission amount of light incident from the backlight unit may be adjusted. The common electrode CE receives a common voltage from the common line CL. In addition, the storage capacitor Cst is provided between the pixel electrode PE and the common electrode CE to maintain a constant voltage difference between the pixel electrode PE and the common electrode CE.

A black matrix and color filters may be formed on the upper substrate 112 of the liquid crystal display panel 100 . However, when the liquid crystal display device is formed in a color filters on tft array (COT) method, the black matrix and color filters may be formed on the lower substrate.

The common electrode CE may be formed on the upper substrate 112 in the case of a vertical electric field driving method such as a TN (Twisted Nematic) mode and a VA (Vertical Alignment) mode. Alternatively, the common electrode CE may be formed on the lower substrate 111 together with the pixel electrode PE in the case of a horizontal electric field driving method such as an in-plane switching (IPS) mode and a fringe field switching (FFS) mode. there is. The liquid crystal display of the present invention may be implemented in any liquid crystal mode as well as TN mode, VA mode, IPS mode, and FFS mode.

As shown in FIG. 3 , a first polarizing plate 103 is attached to the upper substrate 101 of the liquid crystal display panel 100 and a second polarizing plate 104 is attached to the lower substrate 102 . The light transmission axis of the first polarizer 103 intersects or is orthogonal to the light transmission axis of the second polarizer 104 . In addition, an alignment layer for setting a pre-tilt angle of the liquid crystal may be formed on inner surfaces of the upper substrate 101 and the lower substrate 102 in contact with the liquid crystal.

The data driver 110 is connected to data lines D1 to Dm. The data driver 110 receives the modulated digital data DATA' and the data control signal DCS from the timing controller 130, and converts the modulated digital data DATA' to analog data voltages according to the data control signal DCS. convert to The data driver 110 supplies data voltages to the data lines D1 to Dm.

The data driver 110 may include one or more source drive ICs. The source drive IC may be manufactured as a driving chip and mounted on a flexible source film. The source flexible films may be attached on the lower substrate in a tape automated bonding (TAB) method using an anisotropic conductive film, and thus the source drive ICs may be connected to the data lines D1 to Dm. . The source flexible film may be implemented as a tape carrier package or a chip on film. The chip-on film may include a base film such as polyimide and a plurality of conductive lead wires provided on the base film. Each of the source flexible films may be bent or bent.

Alternatively, the source drive IC may be mounted on a lower substrate in a Chip on Glass (COG) method or a Chip on Plastic (COP) method.

The gate driver 120 receives the gate control signal GCS from the timing controller 130 . The gate driver 120 generates gate signals according to the gate control signal GCS and supplies them to the gate lines G1 to Gn.

The gate driver 120 may include a plurality of gate drive integrated circuits (hereinafter referred to as “ICs”). Each of the gate drive ICs may be manufactured as a driving chip. Each of the gate drive ICs may be mounted on a gate flexible film. The gate flexible films may be attached on the lower substrate by a tape automated bonding (TAB) method using an anisotropic conductive film, and thus the gate drive ICs may be connected to the gate lines G1 to Gn. Each of the gate flexible films may be bent or bent.

Alternatively, the gate driver 120 may be formed in the non-display area of the liquid crystal display panel 110 in a gate driver in panel (GIP) method. The non-display area is a peripheral portion of the display area PA and refers to an area in which an image is not displayed.

The timing controller 130 receives digital video data DATA and timing signals. The timing signals include a vertical sync signal to define one frame period, a horizontal sync signal to define one horizontal period, and a data enable signal to indicate valid data. ), and a dot clock, which is a clock signal having a predetermined period.

As shown in FIG. 1 , the timing controller 130 includes an IC ( It may be implemented as an integrated circuit) chip, but is not limited thereto. That is, some or all of the backlight controller 131, the transmittance variable controller 132, and the digital data modulator 133 may not be included in the timing controller 130 and may be implemented as a separate IC chip.

The backlight controller 131 analyzes the digital video data DATA to determine dimming values for each local dimming block. The backlight controller 131 may output backlight control data BCD to the backlight driver 140 to control the light sources to be driven for each local dimming block.

The transmittance variable controller 132 analyzes the digital video data and determines light transmittance for each transmittance control block. The transmittance variable control unit 132 may output transmittance control data TCD to the transmittance variable driving unit 150 to control light transmittance for each transmittance control block. The transmittance control block may be set the same as or different from the local dimming block.

The digital data modulator 133 up-modulates the digital video data DATA to compensate for reduced luminance due to local dimming of the backlight controller. Then, the digital data modulator 133 generates modulated digital data DATA′ by down-modulating the digital video data of blocks whose light transmittance is controlled to be low among the transmittance control blocks in order to increase the effect of local dimming.

The data driving control unit 134 generates a data control signal DCS for controlling the operation timing of the data driving unit 110 . The data driving control unit 134 outputs the modulated digital video data DATA′ and the data control signal DCS to the data driving unit 110 .

The gate driving control unit 135 generates a gate control signal GCS for controlling the operation timing of the gate driving unit 120 . The gate driving controller 135 outputs the gate control signal GCS to the gate driver 20 .

A detailed description of the backlight controller, the transmittance variable controller, and the digital data modulator of the timing controller 130 will be described later with reference to FIGS. 10A, 10B, 11A, 11B, and 12 .

The backlight unit 200 is disposed on the rear surface of the liquid crystal display panel 100 as shown in FIG. 3 and emits uniform light to the rear surface of the liquid crystal display panel 100 . The backlight unit 200 may be implemented as an edge type. The edge type backlight unit 200 has a structure in which a plurality of optical sheets and a light guide plate are disposed under the liquid crystal display panel 100 and a plurality of light sources are disposed on a side surface of the light guide plate. Accordingly, the thickness of the edge-type backlight unit 200 can be reduced compared to a direct-type backlight unit in which light sources are disposed under the liquid crystal display panel 100 .

As shown in FIG. 3 , the backlight unit 200 includes light sources 310 , a light source circuit board 320 , a light guide plate 330 , a reflective sheet 340 , and optical sheets 350 . The backlight unit 200 converts light from the light sources 210 into a uniform surface light source through the light guide plate 220 and the optical sheets 250 and radiates light to the liquid crystal display panel 100 .

The light sources 210 may be implemented as light emitting diodes. The light sources 210 are disposed on at least one side of the light guide plate 220 to emit light to the side of the light guide plate 220 . The light sources 210 are mounted on the light source circuit board 220 and are turned on and off by receiving driving current from the backlight driver 140 . The light source circuit board 220 is connected to the backlight driver 140 .

The light guide plate 220 converts light from the light sources 210 into a surface light source and radiates the light to the liquid crystal display panel 100 . The reflective sheet 240 is disposed on the rear surface of the light guide plate 230 to reflect light from the light guide plate 230 downward toward the light guide plate 230 toward the light guide plate 230 .

Optical sheets 250 are disposed between the light guide plate 230 and the liquid crystal display panel 100 . The optical sheets 250 include one or more prism sheets and one or more diffusion sheets to diffuse the light incident from the light guide plate 230 and to emit light at an angle substantially perpendicular to the light incident surface of the liquid crystal display panel 100. It refracts the propagation path of light so that it is incident. In addition, the optical sheets 250 may include a dual brightness enhancement film.

The case member includes a bottom cover 410 , a support frame 420 , and a top case 430 . When the liquid crystal display device according to the embodiment of the present invention is implemented in a borderless manner, the upper case 430 may be deleted.

The bottom cover 410 is made of metal with a square frame and covers the side and bottom surfaces of the backlight unit 200 as shown in FIG. 3 . The bottom cover 410 may be made of high-strength steel, for example, electro-galvanized steel (EGI), stainless (SUS), galvalume (SGLC), aluminum-plated steel (aka ALCOSTA), tin-plated steel (SPTE), etc. can be made with

The support frame 420 supports a part of the lower surface of the liquid crystal display panel 100 . The support frame 420 may be fixed by being coupled with the bottom cover 410 by a fixing member. The support frame 420 may be made of a square frame in which glass fibers are mixed in a synthetic resin such as polycarbonate, plastic, or made of stainless steel (Steel Use Stainless, SUS). Meanwhile, in order to protect the lower substrate 102 of the liquid crystal display panel 100 from being impacted by the support frame 420, as shown in FIG. 3, a buffer member 440 is interposed between the lower substrate 102 and the support frame 420. ) can be provided.

The upper case 430 covers a portion of the top surface of the liquid crystal display panel 100 , the top and side surfaces of the support frame 420 , and the side surface of the bottom cover 410 . The upper case 430 may be made of electro-galvanized steel (EGI) or stainless steel (SUS). The upper case 430 may be fixed to the bottom cover 410 with hooks or screws.

The backlight driver 140 receives the backlight control data BCD in which dimming values are determined for each local dimming block from the backlight controller 131 of the timing controller 130 . The backlight driver 140 supplies driving current DC to the light sources 210 for each local dimming block. Accordingly, the light sources 210 emit light with a predetermined luminance for each local dimming block. As a result, in the liquid crystal display panel 100, high luminance light is provided to a block displaying a bright image, and light of low luminance is provided to a block displaying a dark image, thereby realizing local dimming properly. Accordingly, in case of using the edge type backlight unit, deterioration in image quality due to implementation of local dimming may be prevented.

The transmittance variable panel 300 is disposed between the liquid crystal display panel 100 and the backlight unit 200 as shown in FIG. 3 . The transmittance variable panel 300 adjusts the transmittance of light incident from the backlight unit 200 to the liquid crystal display panel 100 for each transmittance control block.

The transmittance variable driving unit 150 supplies the first driving voltage DV1 to the first electrode 330 provided on the first substrate 310 of the variable transmittance panel 300 and supplies the second driving voltage DV1 provided on the second substrate 320. The second driving voltage DV2 is supplied to the electrodes 340 .

For example, the first and second driving voltages DV1 and DV2 are not applied to the first and second electrodes 330 and 340 of the variable transmittance panel 300 or supplied to the first electrode 330. When the voltage difference between the first driving voltage DV1 and the second driving voltage DV2 supplied to the second electrode 340 is equal to or less than the reference value, the light transmittance of the variable transmittance panel 300 may be controlled to be the first transmittance. In addition, when the voltage difference between the first driving voltage DV1 supplied to the first electrode 330 of the variable transmittance panel 300 and the second driving voltage DV2 supplied to the second electrode 340 is greater than the reference value, the transmittance rate Light transmittance of the variable panel 300 may be controlled to a second transmittance lower than the first transmittance.

In the case of the edge type backlight unit 200, since the light sources 210 are disposed only on the side surface of the light guide plate 230, there may be blocks in which high luminance light is provided even when a dark image is displayed. Due to this, since local dimming is not properly implemented, image quality degradation may occur. However, in the embodiment of the present invention, by using the variable transmittance panel 300 to lower the light transmittance of a block provided with low luminance light, it is possible to eliminate a block provided with high luminance light even though a dark image is displayed. A detailed description thereof will be described later in conjunction with FIGS. 11A and 11B. Further, a detailed description of the variable transmittance panel 300 will be described later in conjunction with FIGS. 4 to 9 .

4 is a cross-sectional view showing an example of the variable transmittance panel of FIG. 3 . 4 illustrates that the transmittance variable panel 300 varies transmittance in a polarization control method.

Referring to FIG. 4 , the variable transmittance panel 300 includes a first substrate 310, a second substrate 320, a first electrode 330, second electrodes 340, a first alignment layer 350, a first 2 includes an alignment layer 360 , a liquid crystal layer 370 , and a third polarizing plate 380 .

The first and second substrates 310 and 320 are disposed to face each other. Each of the first and second substrates 310 and 320 may be a glass substrate or a plastic film. When each of the first and second substrates 310 and 320 is a plastic film, it is preferable that the third polarizing plate 380 is easily attached to polycarbonate, but is not limited thereto.

At least one first electrode 330 is provided on one surface of the first substrate 310 facing the second substrate 320, and on one surface of the second substrate 320 facing the first substrate 310, the first electrode 330 is provided. Two electrodes 340 are provided. Each of the first and second electrodes 330 and 340 may be a transparent electrode.

The first alignment layer 350 is disposed on the first electrode 330 to cover the first electrode 330, and the second alignment layer 360 covers the second electrodes 340. can be placed on top.

The liquid crystal layer 370 is interposed between the first substrate 310 and the second substrate 320 . The liquid crystal layer 370 may include liquid crystals for driving in a vertical electric field driving method such as a TN (Twisted Nematic) mode and a VA (Vertical Alignment) mode. It is illustrated that the liquid crystal layer 370 includes TN mode liquid crystals.

A third polarizer 360 may be disposed on the other surface opposite to one surface of the second substrate 320 . The light absorption axis of the third polarizer 360 intersects or is orthogonal to the light absorption axis of the second polarizer 104 of the liquid crystal display panel 100 .

That is, in an embodiment of the present invention, the variable transmittance panel 300 may be implemented as a TN mode liquid crystal panel, and thus the first and second driving voltages applied to the first and second electrodes 330 and 340 The light transmittance of the variable transmittance panel 300 may be adjusted by adjusting (DV1, DV2).

For example, in TN mode liquid crystals, the first and second alignment layers 350 and 360 are formed even when the first and second driving voltages DV1 and DV2 are not applied to the first and second electrodes 330 and 340 . It can be arranged in the vertical direction (Y-axis direction) by In this case, the first and second driving voltages DV1 and DV2 are not applied to the first and second electrodes 330 and 340 or the first driving voltage DV1 supplied to the first electrode 330 and When the voltage difference between the second driving voltages DV2 supplied to the second electrode 340 is equal to or less than the reference value, the TN mode liquid crystals may be arranged in a vertical direction (Y-axis direction). In this case, most of the light incident on the variable transmittance panel 300 is absorbed by the second polarizer 104 of the liquid crystal display panel 100 because the polarization direction of light is not modulated by the TN mode liquid crystals. Accordingly, the variable transmittance panel 300 may block most of light incident from the backlight unit 200 .

In addition, a vertical electric field is applied to the TN mode liquid crystals by a voltage difference between the first driving voltage DV1 supplied to the first electrode 330 and the second driving voltage DV2 supplied to the second electrode 340. In this case, the TN mode liquid crystals are twisted according to the vertical electric field and can change the polarization direction of the incident light. That is, the polarization direction of most of the light incident on the variable transmittance panel 300 is modulated by the TN mode liquid crystals, and thus can pass through the second polarizer 104 of the liquid crystal display panel 100 . Accordingly, the variable transmittance panel 300 may adjust transmittance of incident light according to a vertical electric field.

As described above, the vertical electric field can be controlled by adjusting the first and second driving voltages DV1 and DV2 applied to the first and second electrodes 330 and 340, and the variable transmittance panel ( 300) can adjust the light transmittance according to the vertical electric field.

5 is a cross-sectional view showing another example of the variable transmittance panel of FIG. 3 . 5 illustrates that the transmittance variable panel 300 varies transmittance in an optical shutter method.

Referring to FIG. 5 , the variable transmittance panel 300 includes a first substrate 310, a second substrate 320, a first electrode 330, a second electrode 340, an electrochromic layer 390, and a barrier rib. (400).

The first and second substrates 310 and 320 are disposed to face each other. Each of the first and second substrates 310 and 320 may be a glass substrate or a plastic film. When each of the first and second substrates 310 and 320 is a plastic film, it is preferably polyethylene terephthalate (PET), but is not limited thereto.

A first electrode 330 is provided on one surface of the first substrate 310 facing the second substrate 320, and a second electrode 330 is provided on one surface of the second substrate 320 facing the first substrate 310 ( 340) are provided. Each of the first and second electrodes 330 and 340 may be a transparent electrode.

The electrochromic layer 390 is interposed between the first substrate 310 and the second substrate 320 . In the electrochromic layer 390, an electrochemical redox reaction occurs according to the first and second driving voltages DV1 and DV2 applied to the first and second electrodes 330 and 340, thereby causing electrochromic coloration. The color of layer 390 is changed.

For example, when a negative voltage is applied to the first electrode 330 and a positive voltage is applied to the second electrode 340, the electrochromic layer 390 may change to a predetermined color by a reduction reaction. In addition, when a positive voltage is applied to the first electrode 330 and a negative voltage is applied to the second electrode 340, the electrochromic layer 390 may become transparent by an oxidation reaction.

That is, the electrochromic layer 390 of the variable transmittance panel 300 is formed according to voltages applied to the first and second driving voltages DV1 and DV2 applied to the first and second electrodes 330 and 340 . Light transmittance can be adjusted.

The electrochromic layer 390 may be partitioned by the barrier rib 400 . The barrier rib 400 may be omitted. The barrier rib 400 may be an organic film that transmits light.

6 is a cross-sectional view showing another example of the variable transmittance panel of FIG. 3 . 6 illustrates that the transmittance variable panel 300 varies the transmittance in an optical shutter method.

Referring to FIG. 6 , the variable transmittance panel 300 includes a first substrate 310, a second substrate 320, a first electrode 330, a second electrode 340, and a polymer dispersed liquid crystal layer. crystal layer, 500), and barrier ribs 400.

Since the first substrate 310, the second substrate 320, the first electrode 330, and the second electrode 340 are substantially the same as those described in connection with FIG. 5, a detailed description thereof will be omitted.

The polymer dispersed liquid crystal layer 500 is interposed between the first substrate 310 and the second substrate 320 . The polymer dispersed liquid crystal layer 500 includes a plurality of droplets. A plurality of droplets are dispersed by a polymer, and each of the plurality of droplets may include liquid crystals and dichroic dyes. As the ratio of dichroic dyes increases, black expression may be increased, but light transmittance may be reduced and response speed may be slowed. Therefore, the ratio of the dichroic dyes may be appropriately determined through prior experiments in consideration of black expression ability, light transmittance, and response speed.

That is, in an embodiment of the present invention, the variable transmittance panel 300 can be implemented using the polymer dispersed liquid crystal layer 500, and thus the first and second electrodes 330 and 340 are applied. The light transmittance of the variable transmittance panel 300 may be adjusted by adjusting the second driving voltages DV1 and DV2 .

For example, when the first and second driving voltages DV1 and DV2 are not applied to the first and second electrodes 330 and 340, most of the light incident on the variable transmittance panel 300 is dichromatic. It can be absorbed by sexual dyes or scattered by liquid crystals. Accordingly, the variable transmittance panel 300 may block most of light incident from the backlight unit 200 .

In addition, a vertical electric field is applied to liquid crystals and dichroic dyes by a voltage difference between the first driving voltage DV1 supplied to the first electrode 330 and the second driving voltage DV2 supplied to the second electrode 340. When is applied, a ratio of light absorbed by dichroic dyes or scattered by liquid crystals among light incident on the variable transmittance panel 300 may be lowered. Accordingly, the variable transmittance panel 300 may adjust transmittance of incident light according to a vertical electric field.

As described above, the vertical electric field can be controlled by adjusting the first and second driving voltages DV1 and DV2 applied to the first and second electrodes 330 and 340, and the variable transmittance panel ( 300) can adjust the light transmittance according to the vertical electric field.

7 is a cross-sectional view showing another example of the variable transmittance panel of FIG. 3 . 7 illustrates that the transmittance variable panel 300 varies transmittance in an optical shutter method.

Referring to FIG. 7 , the variable transmittance panel 300 includes a first substrate 310, a second substrate 320, a first electrode 330, a second electrode 340, and a guest host liquid crystal layer. layer, 510), and the barrier rib 400.

Since the first substrate 310, the second substrate 320, the first electrode 330, and the second electrode 340 are substantially the same as those described in connection with FIG. 5, a detailed description thereof will be omitted.

The guest host liquid crystal layer 510 is interposed between the first substrate 310 and the second substrate 320 . The polymer dispersed liquid crystal layer 510 may include liquid crystals and dichroic dyes. As the ratio of dichroic dyes increases, black expression may be increased, but light transmittance may be reduced and response speed may be slowed. Therefore, the ratio of the dichroic dyes may be appropriately determined through prior experiments in consideration of black expression ability, light transmittance, and response speed.

That is, according to an embodiment of the present invention, the variable transmittance panel 300 can be implemented using the guest host liquid crystal layer 510, whereby the first and second electrodes 330 and 340 are applied. The light transmittance of the variable transmittance panel 300 may be adjusted by adjusting the two driving voltages DV1 and DV2.

For example, when the first and second driving voltages DV1 and DV2 are not applied to the first and second electrodes 330 and 340, most of the light incident on the variable transmittance panel 300 is dichromatic. It can be absorbed by sexual dyes or scattered by liquid crystals. Accordingly, the variable transmittance panel 300 may block most of light incident from the backlight unit 200 .

In addition, a vertical electric field is applied to liquid crystals and dichroic dyes by a voltage difference between the first driving voltage DV1 supplied to the first electrode 330 and the second driving voltage DV2 supplied to the second electrode 340. When is applied, a ratio of light absorbed by dichroic dyes or scattered by liquid crystals among light incident on the variable transmittance panel 300 may be lowered. Accordingly, the variable transmittance panel 300 may adjust transmittance of incident light according to a vertical electric field.

As described above, the vertical electric field can be controlled by adjusting the first and second driving voltages DV1 and DV2 applied to the first and second electrodes 330 and 340, and the variable transmittance panel ( 300) can adjust the light transmittance according to the vertical electric field.

8 is a plan view illustrating an example of a first electrode and a second electrode of a variable transmittance panel. 8 illustrates that the transmittance variable panel 300 includes a plurality of first electrodes 330 and a plurality of second electrodes 340 .

The plurality of first electrodes 330 are disposed side by side in a first direction (x-axis direction), and the plurality of second electrodes 340 are disposed in a second direction (z-axis direction) crossing the first direction (x-axis direction). ) can be arranged side by side. For this reason, the plurality of first electrodes 330 may cross the plurality of second electrodes 340 .

An electric field may be formed due to the first electrode 330 and the second electrode 340 in an overlapping region where the plurality of first electrodes 330 and the plurality of second electrodes 340 cross each other. Accordingly, an area where the plurality of first electrodes 330 and the plurality of second electrodes 340 overlap each other may be set as the transmittance control block BL2. Accordingly, the transmittance variable panel 300 may set transmittance for each transmittance control block BL2.

9 is a plan view showing another example of the first electrode and the second electrode of the variable transmittance panel. 9 illustrates that the transmittance variable panel 300 includes one first electrode 330 and a plurality of second electrodes 340 .

One first electrode 330 may be disposed on the entire surface of the first substrate 310, and a plurality of second electrodes 340 may be disposed for each transmittance control block BL2. An electric field may be formed due to the first electrode 330 and the second electrode 340 in an area where the first electrode 330 and the plurality of second electrodes 340 overlap each other. Accordingly, an area where the first electrode 330 and the plurality of second electrodes 340 intersect and overlap each other may be set as the transmittance control block BL2.

In particular, each of the plurality of second electrodes 340 may be connected to the variable transmittance driver 150 through the connection line CL. Because of this, since the second driving voltage DV2 can be supplied to each second electrode, the transmittance variable panel 300 can set the transmittance for each transmittance control block BL2.

As described in connection with FIGS. 8 and 9 , in an embodiment of the present invention, the area where the first electrode 330 and the second electrode 340 of the variable transmittance panel 300 overlap each other is defined as a transmittance control block BL2. By setting to , it is possible to simply design without including the thin film transistor. Due to this, the embodiment of the present invention can reduce the manufacturing cost of the variable transmittance panel 300 .

Also, the transmittance control block BL2 of the variable transmittance panel 300 is preferably set to include a plurality of pixels P of the liquid crystal display panel 10 . That is, the size of the transmittance control block BL2 may be set larger than that of the pixel P. Due to this, since precise alignment is not required when attaching the liquid crystal display device 100 and the variable transmittance panel 300, manufacturing cost can be further reduced.

Furthermore, since the variable transmittance panel 300 does not include thin film transistors, formation of opaque metal lines on the variable transmittance panel 300 can be minimized. Therefore, an embodiment of the present invention can prevent moire from occurring due to light interference caused by reflection or refraction of light from the backlight unit 200 on the opaque metal lines of the variable transmittance panel 300. can

10A and 10B are exemplary views illustrating a local dimming block of a backlight unit and a transmittance control block of a variable transmittance panel.

10A and 10B illustrate that the light sources 310 are disposed on only one side of the light guide plate. In this case, the local dimming block BL1 of the backlight unit and the transmittance control block BL2 of the variable transmittance panel may not coincide. 10A and 10B illustrate that the local dimming block BL1 corresponds to five transmittance control blocks BL2 for convenience of explanation, but is not limited thereto.

11A and 11B are exemplary views showing an example of an output image when only local dimming is applied according to an input image and an example of an output image when both local dimming and transmittance variation are applied according to an input image.

11A shows an input image when input digital video data is displayed as it is, a block to which local dimming of a backlight unit is applied, and an actual output image of a liquid crystal display panel.

Referring to FIG. 11A, light sources providing light to the 1-4th and 1-5th blocks BL1-4 and BL1-5 on which a bright circular image is displayed emit light with high luminance, and the remaining blocks Light sources providing light to (BL1-1, BL1-2, BL1-3, BL1-6, BL1-7, BL1-8) emit light with low luminance. The circular bright image is displayed on only some of the 1-4 and 1-5 blocks BL1-4 and BL1-5, but the 1-4 and 1-5 blocks BL1-4 and BL1-5 ) is provided with high luminance light. Accordingly, there is a problem in that regions where dark images are to be displayed in the first to fourth and first to fifth blocks BL1 to 4 and BL1 to 5 actually appear bright as shown in FIG. 11A. That is, in case of using the edge type backlight unit, image quality degradation may occur when local dimming is implemented.

11B shows an input image when input digital video data is displayed as it is, a block to which local dimming of a backlight unit is applied, a transmittance control block in which light transmittance is adjusted in a variable transmittance panel, and an output image of an actual liquid crystal display panel.

Referring to FIG. 11B , light sources providing light to the 1st-4th and 1st-5th blocks BL1-4 and BL1-5 on which the circular bright image BI is displayed emit light with high luminance, Light sources providing light to the remaining blocks BL1-1, BL1-2, BL1-3, BL1-6, BL1-7, and BL1-8 emit light with low luminance. That is, when looking at the transmittance variable block as a reference, the 2-4th, 2-5th, 2-36th, and 2-37th blocks (BL2-4, BL2-5, BL2-36, BL2-37) are low Even though light with high luminance is provided, light with high luminance is provided, resulting in deterioration in image quality. Accordingly, in an embodiment of the present invention, the light transmittance of the 2-4th, 2-5th, 2-36th, and 2-37th blocks is varied by using the variable transmittance panel 300 so that the light transmittance of the backlight unit 200 is changed. block the light

Furthermore, looking at the transmittance variable block as a reference, the 2-12th, 2-13th, 2-28th, and 2-29th blocks (BL2-12, BL2-13, BL2-28, BL2-29) are bright Since pixels displaying an image and pixels displaying a dark image are mixed, it may be desirable to provide medium luminance light to minimize deterioration in image quality. Therefore, the embodiment of the present invention uses the variable transmittance panel 300 to block the 2-12th, 2-13th, 2-28th and 2-29th blocks (BL2-12, BL2-13, BL2-28). , BL2-29), the light transmittance from the backlight unit 200 may be lowered by varying the light transmittance.

As described above, the embodiment of the present invention can lower the transmittance of the transmittance variable block, which does not need to provide high luminance light to display a dark image. As a result, since the embodiment of the present invention properly implements local dimming even in the case of an edge type backlight unit, it is possible to prevent deterioration of image quality due to local dimming.

In addition, the embodiment of the present invention arranges the variable transmittance panel 300 between the liquid crystal display panel 100 and the backlight unit 200, thereby increasing the transmittance of light incident from the backlight unit 200 to the liquid crystal display panel 100. You can control it. That is, in an embodiment of the present invention, since local dimming can be performed using a variable transmittance panel as well as a backlight unit, a static contrast ratio can be further increased.

12 is a flowchart illustrating a method of driving a liquid crystal display according to an exemplary embodiment of the present invention. Hereinafter, a method for driving a liquid crystal display according to an exemplary embodiment of the present invention will be described in detail with reference to FIG. 12 .

First, the backlight controller 131 of the timing controller 130 analyzes digital video data DATA for each preset local dimming block and determines a dimming value for each local dimming block. For example, the backlight controller 131 may calculate an average value of the digital video data DATA for each local dimming block and calculate the average value as a representative value. Alternatively, the backlight control unit 131 may create a histogram of the digital video data DATA for each local dimming block to calculate the most frequent value, and calculate the most frequent value as a representative value. The backlight controller 131 may determine a dimming value by comparing the representative value with preset threshold values. Alternatively, the backlight controller 131 may include a look-up table in which dimming values are stored, and in this case, the dimming value may be received from the look-up table according to the representative value. The backlight controller 131 supplies the backlight control data BCD including dimming values to the backlight driver 140 . (S101 in FIG. 12)

Second, the digital data modulator 133 of the timing controller 130 data stretches the digital video data DATA of one frame period to compensate for the reduced luminance due to local dimming. For example, the digital data modulator 133 may up-modulate the digital video data DATA of one frame period using one of known data stretch algorithms. The digital data modulator 133 outputs the first modulated digital video data to the transmittance variable controller 132 . (S102 in Fig. 12)

Thirdly, the transmittance variable controller 132 of the timing controller 130 analyzes the first modulated digital video data and determines the light transmittance for each transmittance control block. Specifically, the transmittance variable control unit 132 may compare the average value of the firstly modulated digital video data for each transmittance control block with predetermined threshold values to determine how much light transmittance is to be reduced.

For example, as shown in FIG. 11B, the transmittance variable control unit 132 is configured to provide light of high luminance by the backlight control unit 131 at 2-4, 2-5, 2-12, 2-13, The 2-20th, 2-21st, 2-28th, 2-29th, 2-36th and 2-37th blocks (BL2-4, BL2-5, BL2-12, BL2-13, BL2- 20, BL2-21, BL2-28, BL2-29, BL2-36, BL2-37) of the 2-4th, 2-5th, 2-36th and 2-37th blocks (BL2-4, BL2 -5, BL2-36, BL2-37) are blocks to be provided with dark luminance light because they display a black image. In addition, the 2-12th, 2-13th, 2-28th and 2-29th blocks (BL2-12, BL2-13, BL2-28, BL2-29) are pixels displaying bright images and dark Since pixels displaying an image are mixed, it is desirable to provide intermediate luminance light to minimize deterioration of image quality. When the average value of the firstly modulated digital video data of any one transmittance control block is smaller than the first threshold value, the transmittance variable controller 132 determines that the transmittance control block is displaying a black image, and determines that the transmittance control block is displaying a black image. The light transmittance of the control block can be adjusted to the minimum transmittance. In addition, when the average value of the firstly modulated digital video data of any one transmittance control block is greater than or equal to the first threshold value and less than the second threshold value, the transmittance variable control unit 132 sets the light transmittance of the transmittance control block to a minimum value. It can be adjusted to an intermediate transmittance between transmittance and maximum transmittance. The transmittance variable control unit 132 maintains the light transmittance of any one transmittance control block as the maximum transmittance when the average value of the firstly modulated digital video data of any one transmittance control block is equal to or greater than the second threshold value.

The transmittance variable controller 132 outputs transmittance control data TCD including light transmittance information of the transmittance control blocks to the transmittance variable driver 150 and the digital data modulator 133 . (S103 in Fig. 12)

Fourthly, the digital data modulator 133 down-modulates the first modulated digital video data of the transmittance control block adjusted to have the minimum transmittance or medium transmittance so as to lower the light transmittance to increase the effect of local dimming, thereby providing digital modulated data. Create (DATA'). The digital data modulator 133 outputs the digital modulated data DATA' to the data drive controller 134. (S104 in Fig. 12)

As described above, the embodiment of the present invention can lower the transmittance of the transmittance variable block, which does not need to provide high luminance light to display a dark image. As a result, since the embodiment of the present invention properly implements local dimming even in the case of an edge type backlight unit, it is possible to prevent deterioration of image quality due to local dimming.

In addition, the embodiment of the present invention arranges the variable transmittance panel 300 between the liquid crystal display panel 100 and the backlight unit 200, thereby increasing the transmittance of light incident from the backlight unit 200 to the liquid crystal display panel 100. You can control it. That is, in an embodiment of the present invention, since local dimming can be performed using a variable transmittance panel as well as a backlight unit, a static contrast ratio can be further increased.

Although the embodiments of the present invention have been described in more detail with reference to the accompanying drawings, the present invention is not necessarily limited to these embodiments, and may be variously modified and implemented without departing from the technical spirit of the present invention. . Therefore, the embodiments disclosed in the present invention are not intended to limit the technical idea of the present invention, but to explain, and the scope of the technical idea of the present invention is not limited by these embodiments. Therefore, the embodiments described above should be understood as illustrative in all respects and not limiting. The protection scope of the present invention should be construed according to the claims, and all technical ideas within the equivalent range should be construed as being included in the scope of the present invention.

100: liquid crystal display panel 101: upper substrate
102: lower substrate 103: first polarizer
104: second polarizing plate 110: data driver
120: gate driver 130: timing controller
131: backlight controller 132: transmittance variable controller
133: digital data modulation unit 134: data driving control unit
135: gate driving control unit 140: backlight driving unit
150: variable transmittance driving unit 200: backlight unit
210: light source 220: light source circuit board
230: light guide plate 240: reflective sheet
250: optical sheets 410: bottom cover
420: support frame 430: upper case
440: buffer member 300: variable transmittance panel
310: first substrate 320: second substrate
330: first electrode 340: second electrode
350: first alignment layer 360: second alignment layer
370: liquid crystal layer 380: third polarizer
390: electrochromic layer 400: barrier rib
500: polymer dispersed liquid crystal layer 510: guest host liquid crystal layer

Claims (11)

a liquid crystal display panel including a plurality of pixels;
a backlight unit including a plurality of light sources to radiate light to the rear surface of the liquid crystal display panel and driving light sources for each local dimming block based on a dimming value of each of the local dimming blocks;
a backlight controller configured to determine the dimming value for each local dimming block by analyzing digital video data for each local dimming block;
a transmittance variable panel disposed between the liquid crystal display panel and the backlight unit and adjusting transmittance of light incident from the backlight unit to the liquid crystal display panel for each transmittance control block; and
a transmittance variable controller configured to analyze the digital video data for each transmittance control block and determine the light transmittance for each transmittance control block;
The transmittance variable panel,
When the digital video data of any one transmittance control block is smaller than the first threshold value, the light transmittance of any one transmittance control block is controlled to be the first transmittance; Controlling the light transmittance of one transmittance control block to a second transmittance higher than the first transmittance, and controlling the light transmittance of one transmittance control block to the second transmittance when the transmittance is equal to or greater than the second threshold value. According to claim 1,
The local dimming block is different from the transmittance control block. delete According to claim 1,
The transmittance variable panel,
a first substrate having at least one first electrode disposed thereon;
a second substrate on which a plurality of second electrodes are disposed on one surface facing the first substrate; and
A liquid crystal layer interposed between the first and second substrates;
A region where the at least one first electrode and the plurality of second electrodes overlap each other is set as the transmittance control block. According to claim 4,
The liquid crystal display panel further includes a first polarizing plate attached to an upper substrate and a second polarizing plate attached to a lower substrate,
The variable transmittance panel further includes a third polarizer disposed on the other surface of the second substrate,
A light transmission axis of the first polarizer and a light transmission axis of the second polarizer intersect, and a light transmission axis of the second polarizer and a light transmission axis of the third polarizer intersect. According to claim 4,
The liquid crystal layer includes a dichroic dye having a predetermined color. According to claim 1,
The transmittance variable panel,
a first substrate having at least one first electrode disposed thereon;
a second substrate on which a plurality of second electrodes are disposed on one surface facing the first substrate; and
An electrochromic layer interposed between the first and second substrates;
A region where the at least one first electrode and the plurality of second electrodes overlap each other is set as the transmittance control block. According to claim 4 or 7,
The at least one first electrode is disposed in a first direction,
The plurality of second electrodes are arranged in a second direction crossing the first direction. According to claim 4 or 7,
The at least one first electrode is disposed on the entire surface of the first substrate,
The plurality of second electrodes are disposed on one surface of the second substrate in units of transmittance control blocks. According to claim 9,
Receives transmittance control data including the light transmittance information determined for each transmittance control block from the transmittance variable control unit, supplies a first driving voltage to the at least one first electrode according to the light transmittance information, and supplies a first driving voltage to the plurality of first electrodes. Further comprising a variable transmittance panel driver for supplying a second driving voltage to each of the second electrodes,
The variable transmittance panel further includes a connection wire connecting each of the plurality of second electrodes and the variable transmittance panel driver. analyzing digital video data for each local dimming block and determining a dimming value for each local dimming block;
driving light sources of a backlight unit for each local dimming block based on a dimming value determined for each local dimming block;
analyzing the digital video data for each transmittance control block to determine light transmittance for each transmittance control block; and
adjusting transmittance of light input from the backlight unit for each transmittance control block according to the light transmittance determined for each transmittance control block;
The step of adjusting the transmittance of the light input from the backlight unit for each transmittance control block according to the light transmittance determined for each transmittance control block, wherein the digital video data of any transmittance control block reaches a first threshold value through a transmittance variable panel. The light transmittance of any one of the transmittance control blocks is controlled to be the first transmittance when it is less than the first transmittance, and the light transmittance of the transmittance control block is set to be higher than the first transmittance when the transmittance is greater than or equal to the first threshold or smaller than the second threshold. Controlling the second transmittance, and controlling the light transmittance of any one of the transmittance control blocks to the second transmittance when the transmittance is equal to or greater than the second threshold.

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