JPH11264964A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simultaneously perform transmissive display and reflection display by one substrate by switching the lighting state and non-lighting state of a back surface light source by the selection of a display selection means. SOLUTION: A reflection electrode 3 formed of the material of relatively high reflectivity and a transparent electrode 8 formed of the material of relatively high transmissivity are provided on one substrate 1, a counter electrode 4 is formed on the other substrate 2 and a liquid crystal layer 5 composed of a liquid crystal material for indicating negative dielectric constant anisotropy is clamped between the reflection electrode 3 and the transparent electrode 8 and the counter electrode 4. In this case, for both reflection characteristics and transmission characteristics, black display is attained at the time of not applying a voltage, white display is attained at the time of applying the voltage and gradation display is performed by the adjustment of the applied voltage as well. Thus, in both of an area where the reflection electrode 3 is formed and the area where the transparent electrode 8 is formed, the black display is obtained since no double refraction is present in the liquid crystal layer 5 when the voltage is not applied to the liquid crystal layer 5 and the gradation display is made possible by applying the voltage to the liquid crystal layer 5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device used for OA equipment such as a word processor or a personal computer, portable information equipment such as an electronic organizer, or a camera-integrated VTR equipped with a liquid crystal monitor. The present invention relates to a liquid crystal display device that can be used as a transmissive display, a reflective display, or a combination thereof.

[0002]

2. Description of the Related Art A liquid crystal display device is characterized by its thinness and low power consumption, and is characterized by OA equipment such as a word processor and a personal computer, portable information equipment such as an electronic organizer, or a camera having a liquid crystal monitor. Widely used for body VTRs and the like.

The liquid crystal display panel mounted on the liquid crystal display device does not emit light itself unlike a CRT (cathode ray tube) or an EL (electroluminescence) display, and therefore includes an illumination comprising a fluorescent tube called a backlight (back light source). A transmissive liquid crystal display panel in which an image is displayed by controlling the amount of transmission of the backlight with the liquid crystal display panel by installing the device on the back thereof is often used.

However, in the transmission type liquid crystal display panel as described above, the backlight normally consumes 50% or more of the total power consumption of the liquid crystal display panel. Therefore, the provision of the backlight increases the power consumption. I will.

Therefore, apart from the above-mentioned transmissive liquid crystal display panel, in portable information equipment which is often used outdoors or constantly carried, a reflective plate is provided on one substrate instead of the backlight, and ambient light is removed. 2. Description of the Related Art A reflective liquid crystal display panel that performs display by reflecting light on the surface of a reflector is used.

As a display mode used in the reflection type liquid crystal display panel, a polarizing plate such as a TN (twisted nematic) mode and an STN (super twisted nematic) mode which are widely used at present in a transmission type liquid crystal display panel is used. In recent years, a phase change type guest-host mode capable of realizing a bright display because a polarizing plate is not used has been actively developed in recent years.

[0007]

However, the reflection type liquid crystal display panel which performs display using reflected light of ambient light as described above has a problem that visibility is extremely reduced when ambient light is dark. Has disadvantages.

Further, in such a reflection type liquid crystal display panel, display is performed using ambient light for the purpose of low power consumption. Therefore, even in an environment where sufficient power can be supplied, ambient light is lower than a certain limit value. When it is dark, the display cannot be recognized. This was the biggest drawback of the reflection type liquid crystal display panel.

On the other hand, in a transmissive liquid crystal display panel, contrary to a reflective liquid crystal display panel, when ambient light is very bright, display light appears darker than ambient light, and display is recognized. Has the drawback of being difficult to perform.

As described above, for example, in a portable information terminal, a camera-integrated video camera, a still camera, and the like which are required to be used in various environments from a dark place to a bright place, any of the above-mentioned liquid crystal display panels is used. However, it was not satisfactory in terms of usability.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and an object of the present invention is to simultaneously perform transmissive display and reflective display on a single substrate. It is an object of the present invention to provide a liquid crystal display panel which can be used.

[0012]

According to the liquid crystal display device of the present invention, a reflecting portion having a light reflecting function is provided on one of a pair of substrates disposed opposite to each other with a liquid crystal layer interposed therebetween. In a liquid crystal display device in which a pixel electrode that forms a transmission part having a light transmission function in one pixel and a back light source that illuminates the one substrate from the back is arranged, the reflection part functions as a pixel electrode. And display selection means for selecting between a reflection type display to be performed and a transmission type display in which the transmission portion functions as a pixel electrode, and switching between a lighting state and a non-lighting state of the back light source by selecting the display selection means. Thus, the above object is achieved.

In the liquid crystal display device according to the present invention, a reflecting portion having a light reflecting function and a light transmitting function are provided on one of a pair of substrates disposed to face each other with a liquid crystal layer interposed therebetween. A liquid crystal display device in which a pixel electrode that forms a transmission portion within one pixel is formed, and a back light source that illuminates the one substrate from the back is disposed, wherein the reflection portion functions as a pixel electrode. And a display selection unit for selecting a transmission type display in which the transmission unit functions as a pixel electrode, wherein a signal voltage applied to the liquid crystal layer is switched by selection of the display selection unit. Thereby, the above object is achieved.

As described above, the liquid crystal display device of the present invention has a backlight system (back light source) and can switch between a reflective display mode and a transmissive display mode. Specifically, the configuration is such that the back light source is turned on when performing transmissive display, and is turned off when performing reflective display.

In the transmissive display mode and the reflective display mode, the dependence of the transmittance on the applied voltage differs in each case. Therefore, the transmissive display mode and the reflective display mode are different. Is used to switch the input signal. At this time, the reflective electrode (reflective portion) and the transmissive electrode (transmissive portion) corresponding to each pixel electrode formed on the one substrate may be electrically connected to each other. Absent.

The operation of the above configuration will be described below.

In the liquid crystal display device according to the present invention, since one pixel has a pixel electrode having a reflection portion having a light reflection function and a transmission portion having a light transmission function, this reflection portion is formed by a pixel electrode. And a transmissive display in which the transmissive portion functions as a pixel electrode can be simultaneously performed by one liquid crystal display panel.

At this time, there is provided a display selecting means for selecting the above-mentioned reflection type display or the transmission type display, and the display light source is switched between a lighting state and a non-lighting state by selection of the display selecting means. Therefore, when performing transmissive display, the back light source can be turned on, and when performing reflective display, the back light source can be turned off, thereby reducing power consumption.

In addition, there is provided a display selection means for selecting the above-mentioned reflection type display or transmission type display, and the selection of this display selection means switches the signal voltage applied to the liquid crystal layer. The difference in the dependence of the transmittance of the liquid crystal on the applied voltage between the type display and the transmission type display can be cancelled, and good gradation display characteristics can be realized in both types of display.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A liquid crystal display device according to an embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic sectional view showing a liquid crystal display device according to the present embodiment. As shown in FIG. 1, the liquid crystal display device according to the present embodiment
The substrate 1 is provided with a reflective electrode 3 formed of a material having a relatively high reflectance such as Al or Ta and a transparent electrode 8 formed of a material having a relatively high transmittance such as ITO.
A counter electrode 4 is formed on the other substrate 2 opposite to the first electrode 2 and is made of a liquid crystal material exhibiting a negative dielectric anisotropy between the reflection electrode 3 and the transparent electrode 8 and the counter electrode 4. The liquid crystal layer 5 is sandwiched.

On the surfaces of the reflective electrode 3, the transparent electrode 8, and the counter electrode 4 which are in contact with the liquid crystal layer 5, a vertical alignment film (not shown) is formed. After the application, at least one alignment film is subjected to an alignment treatment such as rubbing.

At this time, the liquid crystal molecules constituting the liquid crystal layer 5 are oriented at 0.1 ° with respect to the vertical direction of the substrates 1 and 2 by an alignment treatment such as rubbing of the vertical alignment film.
It has a tilt angle of about 5 °.

Here, the reflecting electrode 3 as a reflecting plate is
Although the reflective electrode 3 is used as an electrode for applying a voltage to the liquid crystal layer 5, the transparent electrode 8 is extended to above the reflective electrode 3 without using the reflective electrode 3 as an electrode, and a voltage is applied to the liquid crystal layer 5 at the reflective portion. It may be an electrode. These electrodes are connected to switching elements using TFTs, and a voltage for displaying an image is applied to the electrodes. The reflective electrode 3 and the transparent electrode 8 corresponding to one pixel region are electrically short-circuited.

The liquid crystal material of the liquid crystal layer 5 is Ne.
A liquid crystal material having a refractive index anisotropy of (refractive index for extraordinary light) = 1.5546 and No (refractive index for normal light) = 1.4773 was used, and the cell gap was set to 3.6 µm.

A quarter-wave plate 7 is disposed on the surface of the substrate 2 opposite to the surface on which the counter electrode 4 is formed. The slow axis of the 波長 wavelength plate 7 is attached to the substrate 2 so as to be inclined by 45 ° with respect to the major axis direction of the liquid crystal molecules when a voltage is applied to the liquid crystal layer 5. A 波長 wavelength plate 10 is disposed on the surface of the substrate 1 opposite to the side on which the reflective electrode 3 and the transparent electrode 8 are formed, and the slow axis of the 波長 wavelength plate 10 is It is attached in a direction parallel to the slow axis of the four-wavelength plate 7.

Further, a polarizing plate 6 is formed on the surface of the ４ wavelength plate 7 opposite to the substrate 2, and similarly, the surface of the 波長 wavelength plate 10 opposite to the substrate 1 is provided with A polarizing plate 9 is formed. At this time, the transmission axes of the polarizing plates 6 and 9 are arranged so as to be parallel to the major axis direction of the liquid crystal molecules when a voltage is applied to the liquid crystal layer 5. The polarization axis 9 is set in the same direction as the slow axis of the 波長 wavelength plate 7 and the 波長 wavelength plate 10.

With such a configuration, the liquid crystal display device according to the present embodiment can perform both black display when no voltage is applied, white display when no voltage is applied, and both the reflection characteristic and the transmission characteristic. It is also possible to perform gradation display by adjusting.

Therefore, in the liquid crystal display device according to the present embodiment, a region where the reflective electrode 3 is formed is a reflective liquid crystal display device, and a region where the transparent electrode 8 is formed is a transmissive liquid crystal. It can be used as a display device. Therefore, when no voltage is applied to the liquid crystal layer 5 in both the region where the reflective electrode 3 is formed and the region where the transparent electrode 8 is formed, the liquid crystal layer 5 has no birefringence, and black display is obtained. By applying a voltage to the layer 5, gradation display is possible.

Next, FIGS. 2A and 2B are diagrams showing the relationship between the applied voltage of the reflection part and the transmission part of the liquid crystal display device according to the present embodiment and the transmittance and the reflectance of the liquid crystal. .

With the above-described configuration, it is possible to realize a transflective liquid crystal display device capable of displaying black when no voltage is applied and displaying white when voltage is applied to both the reflection part and the transmission part. It turns out that it is possible.

However, in such a liquid crystal display device, it should be noted that the dependency of the voltage, the transmittance, and the reflectance of the reflective part and the transmissive part is different.

That is, light is transmitted once through the liquid crystal layer 5 of the liquid crystal display device when performing transmissive display, whereas it is transmitted twice through the liquid crystal layer 5 of the liquid crystal display device when performing reflective display. Since light passes through, when performing reflective display, the change in reflectance with respect to the voltage becomes sharp. as a result,
Although there is no change in the relationship between black and white, there is a problem that the gradation characteristics are different between the case of performing the reflective display and the case of performing the transmissive display. However, the difference between the two causes a serious problem in terms of display quality.

Further, in the case of performing transmissive display rather than the case of performing reflective display, it is possible to increase the transmittance of the liquid crystal by setting a higher driving voltage. As a countermeasure against such a problem, the liquid crystal display device according to the present embodiment is provided with a selecting means for selecting a case of performing a reflective display and a case of performing a transmissive display. The contents of this selection means will be described in detail below.

FIG. 3 is a schematic configuration diagram of the liquid crystal display device according to the present embodiment. Note that the selection means used in the present embodiment may be constituted by a simple switch.

As shown in FIG. 3, the liquid crystal display device used in the present embodiment includes a backlight system, a video signal generation circuit corresponding to a reflection type display, and a video signal generation circuit corresponding to a transmission type display. Are provided.

Here, in these two circuits, the signal level applied to the liquid crystal layer differs depending on the gray scale to be displayed. The video signal generation circuits were designed so that the voltage applied to the liquid crystal was 2.7 V, and the voltage applied during white display was 4.0 V in transmissive display.

Here, the applied voltage is created by, for example, an inverting amplifier circuit using an operational amplifier, and the voltage can be adjusted by changing the ratio of the resistors used. In the present embodiment, a configuration is used in which two types of inverting amplifier circuits are used for performing the reflective display and the transmissive display, and their outputs are switched.

For intermediate gray levels, voltages are set corresponding to the case of transmissive display and the case of reflective display so that desired gray scale display characteristics are obtained.

When the transmissive display mode is selected by the above selection means, the backlight is turned on,
Further, a signal corresponding to the transmissive display is input to the liquid crystal layer.

On the other hand, when the reflection display mode is selected, the backlight is turned off and a signal corresponding to the reflection display is input to the liquid crystal layer.

With this configuration, when the surrounding light is dark, the backlight is turned on, and display is performed using light transmitted through a transparent electrode region formed of a material having a relatively high light transmittance. Display as a transmissive liquid crystal display device becomes possible. In addition, when ambient light is bright, the backlight is turned off, and a reflective liquid crystal display device that performs display using reflected light in a reflective electrode region formed of a material having a relatively high light reflectance is used. Can be displayed.

For the selection between the reflection type display and the transmission type display, the switching operation can be easily performed by providing the liquid crystal display device with a selection means. Liquid crystal display devices such as portable information terminals, camera-integrated video cameras, and still cameras, which are required to be used in a variety of environments from bright to bright places, are fully satisfactory in terms of usability, especially in mid-tones. , And display characteristics excellent in the brightness of each display at the time of reflective display and at the time of transmissive display can be realized.

As shown in FIGS. 2 (a) and 2 (b), the transmittance and the reflectance for each color are different between the case of performing the reflective display and the case of performing the transmissive display. The circuit may be configured to generate a signal corresponding to each color of the display, and the circuit may be switched by the selection unit. Also in this case, the relationship between the gradation and the voltage may be set for each color in such a manner that the transmittance and the reflectance for each color are matched, and this can also be realized by developing the above-described circuit configuration. Become.

[0045]

According to the present invention, since one pixel has a pixel electrode having a reflecting portion having a light reflecting function and a transmitting portion having a light transmitting function, this reflecting portion is used as a pixel electrode. It is possible to simultaneously perform a reflective display to function and a transmissive display to function a transmissive portion as a pixel electrode on a single liquid crystal display panel.

At this time, there is provided a display selection means for selecting the above-mentioned reflection type display or transmission type display, and the display light source is switched between a lighting state and a non-lighting state by selection of the display selection means. Therefore, when performing transmissive display, the back light source can be turned on, and when performing reflective display, the back light source can be turned off, thereby reducing power consumption. I have.

Further, there is provided a display selection means for selecting the above-mentioned reflection type display or transmission type display, and the signal voltage applied to the liquid crystal layer is switched by selecting this display selection means. The difference in the dependence of the transmittance of the liquid crystal on the applied voltage between the type display and the transmission type display can be canceled, and good gradation display characteristics can be realized in either display.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing a liquid crystal display device according to the present embodiment.

FIGS. 2A and 2B are diagrams showing a relationship between an applied voltage of a reflective portion and a transmissive portion of the liquid crystal display device according to the present embodiment, and a transmittance and a reflectance of the liquid crystal.

FIG. 3 is a schematic configuration diagram of a liquid crystal display device according to the present embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2 Substrate 3 Reflecting electrode 4 Counter electrode 5 Liquid crystal layer 6 Polarizer 7 1/4 wavelength plate 8 Transparent electrode 9 Polarizer 10 1/4 wavelength plate

Continued on the front page (72) Inventor Yoji Yoshimura 22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka Inside Sharp Corporation

Claims (2)

[Claims] 1. A reflecting portion having a light reflecting function and a transmitting portion having a light transmitting function are provided in one pixel on one of a pair of substrates arranged to face each other with a liquid crystal layer interposed therebetween. A liquid crystal display device in which a back light source for illuminating the one substrate from the back is disposed, wherein a reflection type display in which the reflection portion functions as a pixel electrode;
A liquid crystal display, comprising: display selection means for selecting a transmission type display in which the transmission portion functions as a pixel electrode, and switching between a lighting state and a non-lighting state of the back light source by selecting the display selection means. apparatus. 2. A reflecting portion having a light reflecting function and a transmitting portion having a light transmitting function are formed in one pixel on one of a pair of substrates arranged to face each other with a liquid crystal layer interposed therebetween. A liquid crystal display device in which a back light source for illuminating the one substrate from the back is disposed, wherein a reflection type display in which the reflection portion functions as a pixel electrode;
A liquid crystal display device comprising: display selection means for selecting a transmission type display in which the transmission part functions as a pixel electrode; and switching the signal voltage applied to the liquid crystal layer by selecting the display selection means.