KR101318079B1 - Liquid Crystal Display with function of controlling Veiwing Angle - Google Patents

Abstract

The present invention relates to a liquid crystal display having a viewing angle adjustment function for expanding the luminance control range in the narrow viewing angle mode and adaptively controlling the brightness of the backlight unit according to the brightness of the surrounding environment in the narrow viewing angle mode.

The liquid crystal display device comprises a liquid crystal panel; A backlight unit radiating light onto the liquid crystal panel; A viewing angle control filter disposed on the liquid crystal panel to adjust brightness of the liquid crystal panel in a wide viewing angle mode and a narrow viewing angle mode; And a backlight controller which senses the brightness of the surrounding environment and adjusts the brightness of the backlight unit according to the brightness of the surrounding environment.

Description

Liquid Crystal Display with function of controlling Veiwing Angle

1 is a view showing a conventional liquid crystal display device.

FIG. 2 is a diagram illustrating an upper electrode of the viewing angle control filter illustrated in FIG. 1.

Figure 3a is a side view of the liquid crystal display shown in Figure 1 in a wide viewing angle mode.

3B is a side view of the liquid crystal display shown in FIG. 1 in the narrow viewing angle mode.

FIG. 4 is a graph showing luminance of the liquid crystal display shown in FIG. 1 in a wide viewing angle mode and a narrow viewing angle mode. FIG.

5 is a view showing a liquid crystal display having a viewing angle adjustment function according to an embodiment of the present invention.

FIG. 6 is a graph illustrating luminance according to side viewing angles of the liquid crystal display having the viewing angle adjusting function illustrated in FIG. 5.

Description of the Related Art

102 lamp 104 lamp housing

106: reflector 108: light guide plate

110: optical sheets 122: top plate

124: lower plate 126, 146: liquid crystal

128, 150: Sealant 130, 132, 148: Polarizer

142: upper substrate 144: lower substrate

201: Optical sensor 202: surrounding environment judging unit

203: luminance control unit 204: inverter

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device, and more particularly, to a liquid crystal display device having a viewing angle adjustment function for expanding a luminance control range in a narrow viewing angle mode and adaptively controlling the brightness of a backlight unit according to the brightness of an environment in the narrow viewing angle mode. It is about.

In general, when the LCD is small, a small number of users often look at the LCD from a limited angle, but as the LCD becomes larger, many users may view the LCD from various angles. As a result, a limited viewing angle characteristic of the liquid crystal display becomes an important problem.

In particular, recently, since the liquid crystal display device is used not only in a private space but also frequently in a public place, the necessity of a narrow viewing angle mode is emerging as necessary for the protection of personal privacy. For example, when using the bank's CD screen, it is necessary to have a narrow viewing angle according to the user's selection.

Accordingly, studies are being conducted to convert the viewing angle of the liquid crystal display device from the wide viewing angle mode to the narrow viewing angle mode. Among them, a viewing angle control filter for switching the viewing angle on the liquid crystal panel has been proposed.

Referring to FIG. 1, a conventional liquid crystal display device includes a liquid crystal panel 40 displaying an image, a backlight unit 20 positioned under the liquid crystal panel 40 to irradiate light to the liquid crystal panel 40, and Located on the liquid crystal panel 40 is provided with a viewing angle adjustment filter 60 for adjusting the viewing angle.

The liquid crystal panel 40 includes an upper plate 22 on which a color filter is formed, a lower plate 24 on which a thin film transistor (TFT) is formed, a liquid crystal 26 injected between the upper plate 22 and a lower plate 24, The upper polarizing plate 30 attached to the upper side of the upper plate 22, the lower polarizing plate 32 attached to the lower side of the lower plate 24, and the upper plate 22 and the lower plate 24 are formed along the outer edge of the liquid crystal panel 40. It consists of a sealant 28 to be bonded.

The backlight unit 20 includes a lamp 2, a lamp housing 4 for reflecting light from the lamp 2 to the light guide plate 8, and a light guide plate for converting light incident from the lamp 2 into a surface light source ( 8) and a reflector 6 which is attached to the rear surface of the light guide plate 8 and reflects the light traveling toward the rear surface of the light guide plate 8 toward the liquid crystal panel 40, and the liquid crystal panel 40 disposed on the light guide plate 8; It is composed of optical sheets 10 for increasing the efficiency of light incident toward the ().

The viewing angle control filter 60 includes an upper substrate 42 on which the upper electrode 52 is formed, a lower substrate 44 on which the lower electrode 54 is formed, and an upper polarizing plate 48 attached to an upper side of the upper substrate 42. The liquid crystal 46 injected between the upper substrate 42 and the lower substrate 44, the sealant 50 for bonding the upper substrate 42 and the lower substrate 44 along the outer edge thereof, and the upper substrate 42. It consists of a polarizing plate 48 attached to the. In the viewing angle control filter 60, the upper electrode 52 is patterned on the upper substrate 42 in an irregular shape as shown in FIG. 2 and is formed of a transparent conductive material, for example, ITO. The lower electrode 54 is formed in the same irregular shape as the upper electrode 52 or is formed on the entire surface of the lower substrate 44. Like the upper electrode 52, the lower electrode 54 is formed of a transparent conductive material, for example, ITO.

When the viewing angle control filter 60 having such a configuration is in an off state, as shown in FIG. 3A, the image viewed at the viewing angle is visible without deterioration of visibility even at the side viewing angle, thereby implementing a wide viewing angle. When 60 is turned on, the image is visible at the viewing angle by the viewing angle control filter 60 as shown in FIG. 3B, but the image of the viewing angle is almost invisible at the side viewing angle, and the electrode of the viewing angle control filter 60 is shown. The pattern shows the narrow viewing angle. In other words, when the viewing angle control filter 60 is in the off state, there is no change in the field of view angle transmittance and the side view angle transmittance of the light emitted from the liquid crystal panel 40, but the view angle control filter ( 60), the luminance of the field of view image which progresses to the side viewing angle is decreased and an irregular electrode pattern is seen.

Conventional liquid crystal display devices have a problem that the brightness of the panel is relatively high in the narrow viewing angle mode when the surrounding environment is dark. In addition, since the range in which the luminance can be adjusted by the viewing angle control filter 60 is very narrow, there is a problem that the viewing angle image may be seen at the side viewing angle when the surrounding environment is bright when the brightness of the backlight unit 20 is bright. .

Accordingly, an object of the present invention is to provide a liquid crystal display device having a viewing angle adjustment function for expanding the luminance control range in the narrow viewing angle mode and adaptively controlling the brightness of the backlight unit according to the brightness of the surrounding environment in the narrow viewing angle mode. .

In order to achieve the above object, a liquid crystal display having a viewing angle adjustment function according to an embodiment of the present invention comprises a liquid crystal panel; A backlight unit radiating light onto the liquid crystal panel; A viewing angle control filter disposed on the liquid crystal panel to adjust brightness of the liquid crystal panel in a wide viewing angle mode and a narrow viewing angle mode; And a backlight controller which senses the brightness of the surrounding environment and adjusts the brightness of the backlight unit according to the brightness of the surrounding environment.

The backlight controller may include an optical sensor for sensing the brightness of the surrounding environment; A surrounding environment determination unit determining the brightness of the surrounding environment according to the output of the optical sensor; And a luminance controller configured to generate luminance control signals generated by at least one of PWM and PAM by comparing the surrounding environment information from the surrounding environment determination unit with a reference value in the narrow viewing angle mode.

The liquid crystal display further includes an inverter that turns on the light source of the backlight unit and controls the light source luminance of the backlight unit under the control of the backlight controller.

The luminance controller lowers the luminance of the light source as the brightness of the surrounding environment is lower in the narrow viewing angle mode.

Other objects and features of the present invention will become apparent from the following description of embodiments with reference to the accompanying drawings.

Hereinafter, exemplary embodiments of the present invention will be described with reference to FIGS. 5 and 6.

Referring to FIG. 5, a liquid crystal display having a viewing angle adjustment function according to an exemplary embodiment of the present invention is provided on a liquid crystal panel 140, a backlight unit 120 disposed below the liquid crystal panel 140, and a liquid crystal panel 140. Arranged between the viewing angle control filter 160, the inverter 204 for driving the light source of the backlight unit 120, the optical sensor 201 for detecting the brightness of the surrounding environment, connected between the optical sensor 201 and the inverter 204 And a surrounding environment determination unit 202 and a brightness control unit 203.

The liquid crystal panel 140 includes an upper plate 122 on which a color filter is formed, a lower plate 124 on which a thin film transistor (TFT) is formed, a liquid crystal 126 injected between the upper plate 122, and a lower plate 124, The upper plate 122 and the lower plate 124 are formed along the outer edge of the upper polarizing plate 130, the lower polarizing plate 132 attached to the lower plate 124, and the liquid crystal panel 140. It consists of a sealant 128 to be bonded.

The backlight unit 120 includes a light source 102, a lamp housing 104 that reflects light from the light source 102 to the light guide plate 108, and a light guide plate 108 that converts light incident from the light source 102 into a surface light source. The reflector 106 is disposed on the light guide plate 108 and reflects light traveling toward the back surface of the light guide plate 108 toward the liquid crystal panel 140. The light is disposed on the light guide plate 108 and incident toward the liquid crystal panel 140. It is composed of optical sheets 110 to increase the efficiency. Although the backlight unit 12 is illustrated as an edge type in the drawing, the backlight unit 12 may be replaced by a direct backlight unit in which a plurality of light sources 102 are disposed below the liquid crystal panel 14 and a diffusion plate is disposed thereon. The light source 102 includes a lamp, such as a cold cathode fluorescent lamp (CCFL) or an external electrode fluorescent lamp (EEFL), and / or a light emitting diode (LED). It is lit by AC drive current.

The lamp housing 104 is formed in such a manner as to wrap the light source 102 and surround the incident surface of the light guide plate 108 to advance the light emitted from the light source 102 to the light guide plate 108. The lamp housing 104 has a reflective surface on its inner surface to reflect light from the light source 102 toward the incident surface of the light guide plate 108. The light guide plate 108 has an exit surface that is horizontal to the inclined back surface, and is formed such that the entrance surface and the exit surface of the light guide plate 108 form a right angle. The light guide plate 108 is generally formed of an acrylic resin (PMMA) having high strength and not easily being deformed or broken and having good transmittance. The reflector 106 serves to reduce light loss by reflecting light incident to itself through the rear surface of the light guide plate 108 toward the light guide plate 108. The optical sheets 110 include a diffusion sheet for diffusing light emitted through the light guide plate 108, and a prism sheet for allowing the light to be incident perpendicularly to the liquid crystal panel.

The viewing angle control filter 160 includes an upper substrate 142 on which the upper electrode 152 is formed, a lower substrate 144 on which the lower electrode 154 is formed, and an upper polarizing plate 148 attached to the upper substrate 142. The liquid crystal 146 injected between the upper substrate 142 and the lower substrate 144, the sealant 150 for bonding the upper substrate 142 and the lower substrate 144 along the outer edge thereof, and the upper substrate 142. It consists of a polarizing plate 148 attached on the. In the viewing angle control filter 160, the upper electrode 152 is patterned on the upper substrate 142 in an irregular shape as shown in FIG. 2, and is formed of a transparent conductive material, for example, ITO. The lower electrode 154 may be patterned in the same irregular shape as the upper electrode 152 or may be formed on the entire surface of the lower substrate 144. Like the upper electrode 152, the lower electrode 154 is formed of a transparent conductive material, for example, ITO. The viewing angle control filter 160 applies a voltage to the electrodes 152 and 154 for applying an electric field to the liquid crystal in the narrow viewing angle mode without affecting the side transmittance of the viewing angle image in the wide viewing angle mode. Lowers the brightness of the image and makes the electrode pattern visible at the side viewing angle.

The inverter 204 converts a DC voltage into an AC voltage and boosts the AC voltage to output AC driving power suitable for lighting of the light source 102. The inverter 204 controls the brightness of the light source 102 under the control of the brightness control unit 203.

The optical sensor 201 detects the brightness of the surrounding environment of the liquid crystal display and outputs a current corresponding to the brightness to the surrounding determination unit 202.

The surrounding environment determining unit 202 converts the output of the optical sensor 201 into a digital signal and compares the digital signal with a reference brightness stored in advance to determine the brightness of the surrounding environment.

The brightness controller 203 forcibly adjusts the brightness of the backlight unit 120 according to a user command input through the user interface or the ambient brightness information from the environment determiner 202. The user command is input through a user interface such as an on screen display (OSD), a keyboard, a mouse, a touch panel, and the like, and a viewing angle mode control signal (Cmode) indicating a wide viewing angle mode and a narrow viewing angle mode or luminance information directly selected by the user Include.

The luminance control unit 203 adjusts the period and frequency of the pulse width modulation signal (Pulse Width Modulation, PWM) for controlling the output of the inverter 204 when the brightness of the surrounding environment is lower than the reference value in the narrow viewing angle mode The brightness of 102 is lowered. In addition, the brightness control unit 203 controls the output of the inverter 204 at the brightness selected by the user by the user command. To this end, the brightness control unit 203 includes a comparator for comparing the reference value and brightness information of the surrounding environment, a PWM signal generating circuit for adjusting the period and frequency of the PWM according to the output of the comparator or a user command. The luminance controller 203 may control the output of the inverter 204 in a pulse amplitude modulation (PAM) scheme. In the case where the light source 102 is selected as the CCFL, the inverter 204 adjusts the tube current of the CCFL between 2.5 and 6.8 mA under the control of the brightness control unit 203. The tube current is controlled to be lower as the brightness of the surrounding environment determined by the optical sensor 201 and the surrounding environment determining unit 202 is less than the reference value and the brightness of the surrounding environment is dark.

As described above, the present invention forcibly lowers the luminance of the backlight unit according to the surrounding environment in the narrow viewing angle mode, thereby significantly lowering the luminance seen at the side viewing angle as shown in FIG. 6. In addition, the liquid crystal display according to the embodiment of the present invention can further narrow the viewing angle for viewing the image of the viewing angle in the narrow viewing angle mode and improve the side narrow viewing angle performance because the surrounding environment adjusts the backlight brightness adaptively to the brightness. Can be.

As described above, the liquid crystal display device having the viewing angle adjustment function according to the present invention can expand the brightness control range and narrow the viewing angle by adjusting the brightness of the backlight unit in the narrow viewing angle mode, and also in the narrow viewing angle mode. By adjusting the brightness of the backlight unit adaptively to the surrounding environment, a narrow viewing angle mode may be realized even in a dark environment.

Those skilled in the art will appreciate that various changes and modifications can be made without departing from the spirit of the present invention. Therefore, the technical scope of the present invention should not be limited to the contents described in the detailed description of the specification, but should be defined by the claims.

Claims (4)

A liquid crystal panel; A backlight unit radiating light onto the liquid crystal panel; A viewing angle control filter disposed on the liquid crystal panel to adjust brightness of the liquid crystal panel in a wide viewing angle mode and a narrow viewing angle mode; And It is provided with a backlight control unit for sensing the brightness of the surrounding environment to adjust the brightness of the backlight unit according to the brightness of the surrounding environment, The backlight unit includes a light source, a light guide plate, a reflecting plate, and optical sheets, The backlight control unit, An optical sensor for sensing the brightness of the surrounding environment; A surrounding environment determination unit determining the brightness of the surrounding environment according to the output of the optical sensor; And A luminance controller configured to generate luminance control signals generated by at least one of PWM and PAM by comparing the surrounding environment information from the surrounding environment determination unit with a reference value in the narrow viewing angle mode; The brightness control unit, And the lower the brightness of the surrounding environment in the narrow viewing angle mode, the lower the brightness of the light source. The liquid crystal display device of claim 1, further comprising an inverter configured to turn on a light source of the backlight unit and to control a light source luminance of the backlight unit under the control of the backlight controller. The liquid crystal display of claim 1, wherein the viewing angle control filter comprises an upper substrate on which an upper electrode is formed, a lower substrate on which a lower electrode is formed, and a liquid crystal injected between the upper substrate and the lower substrate. The liquid crystal display device of claim 3, wherein the upper electrode and the lower electrode are patterned in an irregular shape.

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