KR20050040596A - Liquid crystal display device - Google Patents

Abstract

According to an aspect of the present invention, there is provided a liquid crystal display, comprising: a front light unit including a first light source for supplying light for displaying an image; A second light source provided separately from the first light source of the front light unit; A liquid crystal display panel which receives light from the first light source and the second light source and adjusts the polarization state of the transmitted light according to whether a voltage is applied to perform image display; A first polarizing plate positioned between the front light unit and the liquid crystal display panel and having a transmission axis in a first direction; A second polarizing plate provided on an opposite side of the first polarizing plate with respect to the liquid crystal display panel and having a transmission axis in a second direction; And a selective reflection / transmitting part positioned between the liquid crystal display panel and the second polarizing plate and selectively reflecting / transmitting according to the polarization state of light passing through the liquid crystal display panel; And selective reflection / transmission of light incident from the selective reflection / transmission unit, wherein the second light source is turned on when the reflection mode is driven to display an image on the front surface of the liquid crystal display. The first light source is turned on when the first display mode and the transmission mode are driven to display an image in both directions of the second display mode in which an image is displayed on the rear surface of the LCD.

Description

Liquid crystal display device

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device. In particular, an image is displayed in both directions of the front direction and the rear direction by reflection / transmission of a liquid crystal display panel using one liquid crystal display panel. The present invention relates to a liquid crystal display device capable of removing the moiré phenomenon.

In general, the liquid crystal display is a flat panel display having advantages of small size, thinness, and low power consumption, and is used as a portable computer such as a notebook PC, office automation equipment, and audio / video equipment.

Such a liquid crystal display device displays an image or an image by controlling an electric field applied to a liquid crystal material having dielectric anisotropy to transmit or block light. Liquid crystal display devices, unlike display elements that emit light by themselves, such as electro-luminescence (EL), cathode ray tube (CRT), and light emitting diode (LED), emit light by themselves. It does not occur and uses external light.

In general, liquid crystal displays are roughly classified into a transmissive type and a reflective type according to a method of using light. The transmissive liquid crystal display device includes a liquid crystal display panel in which a liquid crystal material is injected between two glass substrates, and a backlight for supplying light to the liquid crystal display panel.

As is known, the driving principle of the liquid crystal display device utilizes the optical anisotropy and polarization properties of the liquid crystal. Since the liquid crystal is thin and long in structure, the direction of the molecular arrangement can be controlled by artificially applying an electromagnetic field to the liquid crystal molecules having directionality and polarization in the molecular arrangement. Therefore, if the alignment direction is arbitrarily adjusted, light may be transmitted or blocked according to the alignment direction of the liquid crystal molecules by optical anisotropy of the liquid crystal, thereby displaying colors and images.

The active matrix liquid crystal display device adds an active element having a nonlinear characteristic to each pixel arranged in a matrix form, and controls the operation of each pixel by using the switching characteristics of the element. The memory function is implemented through.

On the other hand, in recent years, various studies have been sought for a bidirectional display device (dual display) capable of displaying an image in both front and rear parts of a liquid crystal display device.

According to the present invention, the moiré phenomenon can be eliminated by turning on a separate light source in the reflection mode in displaying an image in both the front direction and the rear direction by the reflection / transmission of the liquid crystal display panel using one liquid crystal display panel. It is an object of the present invention to provide a liquid crystal display and a driving method thereof.

Another object of the present invention is to provide a selective reflection / transmission optical element capable of selectively reflecting or transmitting incident light according to a linearly polarized state of incident light.

In order to achieve the above object, the liquid crystal display device according to the present invention,

A front light unit comprising a first light source for supplying light for displaying an image; A second light source provided separately from the first light source of the front light unit; A liquid crystal display panel which receives light from the first light source and the second light source and adjusts the polarization state of the transmitted light according to whether a voltage is applied to perform image display; A first polarizing plate positioned between the front light unit and the liquid crystal display panel and having a transmission axis in a first direction; A second polarizing plate provided on an opposite side of the first polarizing plate with respect to the liquid crystal display panel and having a transmission axis in a second direction; And a selective reflection / transmitting part positioned between the liquid crystal display panel and the second polarizing plate and selectively reflecting / transmitting according to the polarization state of light passing through the liquid crystal display panel; It is configured to include,

In the selective reflection / transmission of the light incident from the selective reflection / transmitter, the first display mode and transmission for displaying an image on the front surface of the liquid crystal display by turning on the second light source when driving the reflection mode The first light source is turned on when the mode is driven to display the image in both directions of the second display mode in which the image is displayed on the rear surface of the LCD.

In addition, the liquid crystal display device driving method according to the present invention in order to achieve the above object,

Receiving light emitted from the light source and changing the incident light into linearly polarized light; Allowing the light in the linearly polarized state to be incident on the liquid crystal display panel and controlling the linearly polarized state of the light passing through the liquid crystal display panel through the presence or absence of voltage; And allowing the light transmitted through the liquid crystal display panel to be incident on the selective reflection / transmission unit, and selectively reflecting or transmitting the light incident on the selective reflection / transmission unit according to the linearly polarized state of the light transmitted through the liquid crystal display panel. Making a step; Driving the liquid crystal display device, including

In the selective reflection / transmission of the light incident from the selective reflection / transmitter, a first display mode and a transmission mode in which a second light source is turned on to display an image on the front surface of the liquid crystal display when driving the reflection mode In operation, the first light source is turned on to display an image in both directions of a second display mode in which an image is displayed on a rear surface of the LCD.

In addition, the selective reflection / transmission optical element according to the present invention in order to achieve the above another object,

CLC film for selectively transmitting / reflecting left circularly polarized light or right circularly polarized light according to the polarization characteristic of incident light; A first phase difference compensation film provided on the front surface of the CLC film and generating a phase difference of λ / 4 with respect to incident light; And a second phase difference compensation film provided on a rear surface of the CLC film and generating a phase difference of λ / 4 with respect to incident light. It is configured to include,

According to the linearly polarized light characteristic of the light incident on the first retardation compensation film, all the light linearly polarized in the first direction is transmitted, and when the linearly polarized light is incident by 90 degrees from the first direction, all the light is reflected. It has its features.

According to the present invention, there is an advantage that the image can be displayed in both directions of the front and rear of the liquid crystal display panel using one liquid crystal display panel.

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

1 is a view schematically showing the configuration of a liquid crystal display according to the present invention.

As shown in FIG. 1, the liquid crystal display according to the present invention is configured to display an image in both directions of a front portion and a rear portion of the liquid crystal display using one liquid crystal display panel 130. In addition, a front light unit 110 is attached to a front surface of the liquid crystal display, and a first light source 111 is provided on a side surface of the front light unit 110. In addition, a second light source 112 is provided above the first light source 111.

Here, the front surface of the front light unit 110 is formed to have a transmittance of about half of a transparent material. Accordingly, light emitted from the first light source 111 or the second light source 112 may be reflected from the front surface of the front light unit 110 to propagate toward the rear portion of the liquid crystal display, and may be incident from the outside. Light may be incident on the liquid crystal display panel 130.

In the liquid crystal display according to the present invention, polarizers are provided in the front direction and the rear direction of the liquid crystal display panel 130, respectively. The first polarizer 120 is provided in the front direction of the liquid crystal display panel 130. The transmission axis of the) and the transmission axis of the second polarizing plate 170 provided in the back direction are provided to be different from each other by 90 degrees. In FIG. 1, the first polarizing plate 120 provided in the front direction of the liquid crystal display panel 130 is provided to transmit light linearly polarized in the y-axis direction with respect to incident light. The second polarizing plate 170 provided in the back direction shows an example provided to transmit light linearly polarized in the x-axis direction with respect to incident light.

In addition, the liquid crystal display according to the present invention includes a selective reflection / transmitting portion to select the reflection and transmission of light using polarization characteristics in order to implement a double-sided display function through one liquid crystal display panel 130. In the selective reflection / transmitting unit, the propagation direction of the light (front side or rear side) is determined, and the direction in which the image is displayed is determined. Here, as shown in FIG. 1, the selective reflection / transmission part includes a first phase difference compensation film 140 that generates a phase difference of λ / 4 with respect to incident light, a CLC (Cholesteric Liquid Crystal) film 150, and incident light. And a second retardation compensation film 160 which generates a retardation of λ / 4 with respect to light to be formed. For example, the retardation compensation film may be composed of a QWP (Quarter Wave Plate).

On the other hand, as is known, the phase difference compensation film for generating a phase difference of λ / 4 with respect to the incident light, the linearly polarized light is incident to the circularly polarized light, the circularly polarized light incident to the linearly polarized light function Do this. In addition, the CLC film may selectively reflect / transmit right-handed circularly polarized light (RHC) or left-handed circularly polarized light (LHC). In the present invention, in consideration of the polarized direction (circular polarization or left circular polarization) of the circularly polarized light, it is intended to use a characteristic that is selectively reflected or transmitted according to the circularly polarized property of the light to proceed.

In order to realize such selective reflection / transmission characteristics, the optical elements of the selective reflection / transmission portion are arranged as shown in FIG. 2 as an example. 2 is a view showing an optical axis arrangement of the optical element employed in the liquid crystal display according to the present invention.

Referring to FIG. 2, the selective reflection / transmission optical device includes a first retardation compensation film 140, a CLC film 150, and a second retardation compensation film 160, and the second retardation compensation film 160. ), A second polarizing plate 170 is provided. In this case, an optical axis of the first retardation compensation film 140 may be formed at an angle of 45 degrees with respect to the liquid crystal alignment direction (x axis) of the liquid crystal display panel 130, and the second retardation compensation film ( The optical axis of 160 is provided to form an angle of −45 degrees with respect to the x axis. The transmission axis of the second polarizing plate 170 is provided to coincide with the x-axis direction.

The selective reflection / transmission optical element having such a configuration performs the following functions.

That is, according to the linearly polarized light characteristic of the light incident on the first retardation compensation film 140, all the light linearly polarized in the first direction is transmitted, and when the linearly polarized light is incident by 90 degrees from the first direction. It performs the function of reflecting all.

In addition, when the light incident on the first retardation compensation film 140 is linearly polarized light in the first direction, all the incident light passes through the second retardation compensation film 160, and the transmitted light is Light linearly polarized in the first direction. In addition, when the light incident on the first retardation compensation film 140 is linearly polarized light in a 90 degree difference from the first direction, all incident light is reflected to pass through the first retardation compensation film 140. The reflected light becomes light linearly polarized by 90 degrees from the first direction.

As described above, the principle in which reflection or transmission is implemented according to the linearly polarized state of the incident light will be described in detail with reference to driving of the liquid crystal display.

Then, in the liquid crystal display device having such a configuration, an operation for the case where the voltage is applied to the liquid crystal display panel and when the voltage is not applied will be described in detail.

First, a case in which no voltage is applied to the liquid crystal display panel 130 will be described with reference to FIGS. 3 and 4. 3 is a view for explaining the operation of the liquid crystal display device when the voltage is not applied to the liquid crystal display panel employed in the liquid crystal display device according to the present invention, Figure 4 is employed in the liquid crystal display device according to the present invention In the case where no voltage is applied to the liquid crystal display panel, the polarization state of light propagated in each area of the liquid crystal display device is illustrated.

Referring to FIGS. 3 and 4, when no voltage is applied to the liquid crystal display panel 130, the first light source 111 of the front light unit 110 is turned on in the transmissive mode, and the first light source 111 is turned on. 2 The light source 112 is turned off.

Therefore, the light emitted from the first light source 111 is linearly polarized in the y-axis direction while passing through the first polarizing plate 120, and linearly polarized in the x-axis direction while passing through the liquid crystal display panel 130. (⊙ notation).

In addition, the light linearly polarized in the x-axis direction while passing through the liquid crystal display panel 130 is changed into right circularly polarized light (RHC notation) while passing through the first retardation compensation film 140.

On the other hand, the right circularly polarized light (RHC notation) passes through the first retardation compensation film 140 to meet the CLC film 150 and transmit all of them. The CLC film 150 may be implemented by reflecting the left circularly polarized light and transmitting the right circularly polarized light.

Accordingly, the right circularly polarized light (RHC notation) passing through the CLC film 150 is changed to light polarized linearly in the x-axis direction while passing through the second retardation compensation film 160. As described above, the light polarized linearly in the x-axis direction (circle notation) while passing through the second retardation compensation film 160 may pass through the second polarizing plate 170 having the x-axis as the transmission axis.

As a result, when power is not applied to the liquid crystal display panel 130, all of the light is transmitted through the rear part of the liquid crystal display device implemented by the transmission mode driving, and thus the liquid crystal is implemented by the reflection mode driving. The front part of the display device is 'black' state because there is no reflected light. By driving the liquid crystal display device as described above, it is possible to implement a double-side display device using one liquid crystal display panel.

5 and 6, a case in which a voltage is applied to the liquid crystal display panel will be described below. 5 is a view for explaining the operation of the liquid crystal display when a voltage is applied to the liquid crystal display panel employed in the liquid crystal display according to the present invention, Figure 6 is used in the liquid crystal display according to the present invention In the case where a voltage is applied to the liquid crystal display panel, the polarization state of light propagated in each area of the liquid crystal display device is illustrated.

Referring to FIGS. 5 and 6, when a voltage is applied to the liquid crystal display panel 130, the first light source 111 of the front light unit 110 is turned off in the reflection mode and the second light source is turned off. The light source 112 is turned on to serve as an external light source.

If the first light source 111 of the front light unit 110 is turned on and the emitted light is totally reflected from the light guide plate of the front light unit 110 and is incident vertically into the liquid crystal display panel 130, the front A moire phenomenon in which streaks appear on a screen displayed by a pattern of a predetermined rule of the light guide plate portion of the unit 110 of the light or a black matrix pattern of the color filter of the liquid crystal display panel is generated.

Here, the moire phenomenon refers to an interference fringe that is formed when two or more periodic patterns overlap, and overlaps two or more similarly spaced grids to shine light. This is a stripe with a large period separate from the two grids.

Therefore, when the second light source 112 is provided on the upper portion of the first light source 111 and lights, the light source acts as an external light source so that light directly reflected from the light guide plate of the front light unit 110 is reflected on the liquid crystal display. Since the light is not vertically incident on the panel 130, the moiré phenomenon does not appear.

Meanwhile, the light emitted from the second light source is linearly polarized in the y-axis direction while passing through the first polarizing plate 120, and no change occurs while passing through the liquid crystal display panel 130. Accordingly, the state of light polarized linearly in the y-axis direction is maintained.

The linearly polarized light in the y-axis direction passing through the liquid crystal display panel 130 is changed to left circularly polarized light (LHC notation) while passing through the first retardation compensation film 140.

Meanwhile, the left circularly polarized light (LHC notation) passing through the first retardation compensation film 140 meets the CLC film 150 and reflects all of them. The CLC film 150 may be implemented by reflecting the left circularly polarized light and transmitting the right circularly polarized light. In this case, since the light reflected from the CLC film 150 reflects light in the same circular polarization state as that of the incident circularly polarized light, the left circularly polarized light is reflected to the liquid crystal display device. Will be facing the front of the.

In addition, the left circularly polarized light (LHC notation) reflected by the CLC film 150 passes through the first retardation compensation film 140. Since the first retardation compensation film 140 is incident from the rear surface, the optical axis Has an angle of 135 degrees with respect to the x-axis. Accordingly, the light passing through the first retardation compensation film 140 is changed into light linearly polarized in the y-axis direction.

If the light propagation characteristics are analyzed using the Jone's matrix, they can be expressed as follows. That is, since light incident on the front surface of the first retardation compensation film 140 is linearly polarized light (으로), the light is incident on the front surface of the first retardation compensation film 140 and again. Reentry from the back can be expressed as In this calculation, the light finally passing through the first retardation compensation film 140 and incident on the liquid crystal display panel 130 becomes light linearly polarized on the y-axis.

The light polarized on the y-axis passes through the liquid crystal display panel 130 which is optically inactive, and thus no change occurs in the polarization state. It will penetrate all 120).

As a result, when a voltage is applied to the liquid crystal display panel 130, all the light is reflected at the front part of the liquid crystal display device implemented by the reflection mode driving, and the liquid crystal is implemented by the transmission mode driving. Since no light is transmitted from the rear of the display device, the display device becomes 'black'. By driving the liquid crystal display device as described above, it is possible to implement a double-side display device using one liquid crystal display panel.

In the configuration of the liquid crystal display panel 130 employed in the present invention, the first substrate with a color filter, the liquid crystal layer, and the second substrate with a TFT array are provided from the direction of the front light unit 110. It can be arranged sequentially. In addition, in the configuration of the liquid crystal display panel 130 employed in the present invention, the first substrate with a TFT array, the liquid crystal layer, and the second substrate with a color filter are arranged from the direction of the front light unit 110. It can also be arranged sequentially.

In this case, a glass or plastic substrate subjected to low reflection treatment may be used as the substrate on which the first substrate and the second substrate are formed. In addition, the black matrix material provided in the liquid crystal display panel 130 may also use a material having low reflection characteristics with respect to the light emitted from the front light unit 110, and optical elements employed in each polarization part may also be used. It has a low reflection characteristic.

On the other hand, the liquid crystal display having such a configuration can be used as a double-sided display element, when applied to a mobile communication terminal (mobile portable communication, PDA, etc.), the image is displayed in both the front direction and the rear direction of the liquid crystal display panel You can do it. Accordingly, more various video display functions can be implemented in the mobile communication terminal. For example, in the case of a folder type mobile communication terminal, the direction in which an image is displayed may be set differently when a folder is opened or closed. In the case of a sliding type mobile communication terminal, the direction in which the image is displayed may be set differently according to the sliding degree of the image display unit.

According to the liquid crystal display device according to the present invention as described above, to display the image in both the front direction and the rear direction by the reflection / transmission of the liquid crystal display panel using a single liquid crystal display panel, separately in the reflection mode The moire phenomenon can be removed by turning on the light source.

In addition, according to the liquid crystal display device according to the present invention, by using a single liquid crystal display panel to display the image in both the front direction and the rear direction, the thickness of the bi-directional display device can be made thinner, the manufacturing cost can be lowered There is an advantage.

1 is a view schematically showing the configuration of a liquid crystal display according to the present invention.

2 is a view showing an optical axis arrangement of the optical element employed in the liquid crystal display device according to the present invention.

3 is a view for explaining the operation of the liquid crystal display when no voltage is applied to the liquid crystal display panel employed in the liquid crystal display according to the present invention.

4 is a view for explaining a polarization state of light propagated in each area of a liquid crystal display when no voltage is applied to the liquid crystal display panel employed in the liquid crystal display according to the present invention.

5 is a view for explaining the operation of the liquid crystal display when a voltage is applied to the liquid crystal display panel employed in the liquid crystal display according to the present invention.

6 is a view for explaining a polarization state of light propagated in each area of the liquid crystal display when a voltage is applied to the liquid crystal display panel employed in the liquid crystal display according to the present invention.

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

110 ... Front light unit 111 ... First light source

112 second light source 120 first polarizer

130 LCD panel 140 First retardation film

150 ... CLC film 160 ... second phase difference compensation film

170 ... second polarizer

Claims (10)

A front light unit comprising a first light source for supplying light for displaying an image; A second light source provided separately from the first light source of the front light unit; A liquid crystal display panel which receives light from the first light source and the second light source and adjusts the polarization state of the transmitted light according to whether a voltage is applied to perform image display; A first polarizing plate positioned between the front light unit and the liquid crystal display panel and having a transmission axis in a first direction; A second polarizing plate provided on an opposite side of the first polarizing plate with respect to the liquid crystal display panel and having a transmission axis in a second direction; And a selective reflection / transmitting part positioned between the liquid crystal display panel and the second polarizing plate and selectively reflecting / transmitting according to the polarization state of light passing through the liquid crystal display panel; It is configured to include, In the selective reflection / transmission of the light incident from the selective reflection / transmitter, the first display mode and transmission for displaying an image on the front surface of the liquid crystal display by turning on the second light source when driving the reflection mode And displaying the image in both directions of the second display mode in which the first light source is turned on to display an image on the rear surface of the liquid crystal display. The method of claim 1, And the first light source is provided at a side of the front light unit, and the second light source is formed at a position above the first light source. The method of claim 1, And a transmission axis in a first direction provided in the first polarizing plate and a transmission axis in a second direction provided in the second polarizing plate are arranged such that a difference of 90 degrees occurs. The method of claim 1, The selective reflection / transmission unit, CLC film for selectively transmitting / reflecting left circularly polarized light or right circularly polarized light according to the polarization characteristic of incident light; A first phase difference compensation film provided on the front surface of the CLC film and generating a phase difference of λ / 4 with respect to incident light; And A second phase difference compensation film provided on a rear surface of the CLC film and generating a phase difference of λ / 4 with respect to incident light; Liquid crystal display comprising a. The method of claim 4, wherein And the first retardation compensation film and the second retardation compensation film are formed of a QWP (Quarter Wave Plate). The method of claim 4, wherein And the first retardation compensation film and the second retardation compensation film are arranged to have optical axes that are 90 degrees apart from each other. Receiving light emitted from the light source and changing the incident light into linearly polarized light; Allowing the light in the linearly polarized state to be incident on the liquid crystal display panel and controlling the linearly polarized state of the light passing through the liquid crystal display panel through the presence or absence of voltage; And allowing the light transmitted through the liquid crystal display panel to be incident on the selective reflection / transmission unit, and selectively reflecting or transmitting the light incident on the selective reflection / transmission unit according to the linearly polarized state of the light transmitted through the liquid crystal display panel. Making a step; Driving the liquid crystal display device, including In the selective reflection / transmission of the light incident from the selective reflection / transmitter, a first display mode and a transmission mode in which a second light source is turned on to display an image on the front surface of the liquid crystal display when driving the reflection mode And driving the first light source to display images in both directions of a second display mode in which the first light source is turned on to display an image on the rear surface of the LCD. The method of claim 7, wherein The selective reflection / transmission unit, CLC film for selectively transmitting / reflecting left circularly polarized light or right circularly polarized light according to the polarization characteristic of incident light; A first phase difference compensation film provided on the front surface of the CLC film and generating a phase difference of λ / 4 with respect to incident light; And a second phase difference compensation film provided on a rear surface of the CLC film and generating a phase difference of λ / 4 with respect to incident light. It consists of A method of driving a liquid crystal display device, characterized in that the selective reflection or transmission according to the linear polarization characteristics of the input light. The method of claim 7, wherein The first retardation compensation film and the second retardation compensation film is a driving method of the liquid crystal display device, characterized in that consisting of a QWP (Quarter Wave Plate). The method of claim 7, wherein And the first retardation compensation film and the second retardation compensation film are arranged to have optical axes that are 90 degrees apart from each other.