JPH06332386A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To provide a liquid crystal display device selectively switching an optimum display system corresponding to surrounding brightness. CONSTITUTION:This device is constituted of a back light 3 arranged on the rear of a liquid crystal panel 2 and irradiating the liquid crystal panel 2 from the rear, a reflection/transmission selection member 4 interposed between the liquid crystal panel 2 and the back light 3, and performing any operation of the reflection of an incident light from the display surface of the liquid crystal panel 2 or the transmission of the light radiated from the back light 3, a photodetecting means 5 detecting the light quantity of external light irradiating the liquid crystal panel 2 and a switching means 6 selectively switching between the operations of the reflection and the transmission of the reflection/ transmission selection member 4 based on the light quantity detected by the photodetecting means 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,
In particular, the present invention relates to a liquid crystal display device that employs an optimal display method for the intensity of ambient light (external light).

BACKGROUND OF THE INVENTION In recent years, information processing apparatuses represented by, for example, word processors (hereinafter simply referred to as word processors) and personal computers (hereinafter simply referred to as personal computers) have become more sophisticated and smaller in size. The size of the main body is smaller than desktop type such as desktop type and laptop type called knee type, and even smaller than A4 file size called A4 file size and A4 just size word processor PC and notebook type. Like the portable information processing device called palmtop type / electronic notebook type of
The size of the information processing apparatus is becoming smaller and smaller, and it is desired that the display portion of the information processing apparatus be lightweight and thin.

Therefore, as such a display device, a conventional cathode ray tube (hereinafter, CRT: Ca
For example, a liquid crystal display device as shown in FIG. 5 has been widely used in place of the (thode Ray Tube).

The display systems of liquid crystal display devices are roughly classified into
A reflective liquid crystal display device that secures the contrast of the liquid crystal display surface by reflecting ambient light, and a transmissive type that secures the contrast of the liquid crystal display surface by illuminating light from the back surface of the liquid crystal panel with a backlight. There is a liquid crystal display device.

The reflection type liquid crystal display device uses ambient light (external light).
Therefore, when ambient light (external light) is extremely dark like nighttime use, external illumination light is required separately, and it is suitable for use in a relatively bright place.

On the other hand, a transmissive liquid crystal display device provided with a backlight is popular because it is advantageous in contrast and visibility in comparison with a reflective liquid crystal display device, and is generally used. In order to provide an easy-to-read screen that is not affected by the ambient brightness, it is common to have a light source on the back of the liquid crystal panel and illuminate this liquid crystal panel from the back, a so-called backlight. ing.

[0007]

2. Description of the Related Art As a structure of a backlight, a light source is arranged at the back position of a liquid crystal panel and the liquid crystal panel is directly illuminated from the back surface (see FIG. 6A), and a light source is provided at a side position of the liquid crystal panel. There is a side light (or edge light) system (refer to FIG. 6B) in which the light from the light source is guided to the back surface of the liquid crystal panel and is indirectly irradiated. In FIG. 6, a is a fluorescent lamp, b is a diffusion plate, and c.
Is a light guide plate.

The direct type has a high light utilization efficiency and high brightness, but has a low light utilization efficiency because of the influence of heat on the LCD and the difficulty of thinning the display device itself. A side light system, which has a feature of high brightness uniformity, is often used as a backlight.
By the way, fluorescent lamps used as a light source of a backlight include a cold cathode tube and a hot cathode tube. Although the hot cathode tube can obtain high brightness, the cold cathode tube is often used in terms of heat generation and life. There is.

Conventionally, as a transmissive liquid crystal display device provided with this type of sidelight type backlight, for example, there is a liquid crystal display device 101 as shown in FIG. Note that FIG. 7 is a cross-sectional view of a liquid crystal module including a conventional sidelight type backlight.

As shown in FIG. 7, the liquid crystal display device 101
Are roughly divided into a liquid crystal panel 102 and a backlight 10.
3 and 3.

The liquid crystal panel 102 includes polarizing plates 104 and 10.
5 and glass substrates 106 and 107, and electrodes, liquid crystal cells and the like are formed between the glass substrates 106 and 107.

The backlight 103 comprises a fluorescent lamp 110 serving as a light source, a lamp holder 111, a light guide plate 112, a reflection plate 113, and a diffusion plate 114.

The fluorescent lamp 110 includes a cold cathode FL (FLuore).
scent) lamp, which is arranged at the end portion of the light guide plate 112 and is covered by the lamp holder 111 except the end surface position of the light guide plate 112.

The lamp holder 111 is formed so that light is reflected inside the lamp holder 111, and the portion corresponding to the end face position of the light guide plate 112 is efficiently irradiated with light emitted from the fluorescent lamp 110 in one direction. Is configured.

The light guide plate 112 is made of a transparent acrylic plate and guides the light entering from the end surface to the back surface of the liquid crystal panel 102, and a dot pattern is printed on the back surface of the light guide plate 112 to form a print pattern. The amount of light emitted from each portion is adjusted according to the print density.

The reflection plate 113 is for preventing the light entering the light guide plate 112 from passing through the back surface of the light guide plate 112 and going out, and the diffusion plate 114 is the light guided by the light guide plate 112. When the liquid crystal panel 102 is irradiated with the light, the light is diffused to balance the brightness.

In the above structure, the light entering from the end face of the light guide plate 112 is repeatedly reflected and proceeds in the light guide plate 112 (acrylic plate) due to the difference in the refractive index between acrylic and air, and the ink is printed. Since the reflectance changes in the part,
Light is emitted from the light guide plate 112 (acrylic plate) to the surface.

By the way, when the distance from the fluorescent lamp 110, which is the light source, increases, the light attenuation increases, and unless the printing density is increased, the light source (in this case, the end face position of the light guide plate 112)
Since the same amount of light as near the
The print pattern printed on 2 is a print pattern for making the optical system efficient.

[0019]

However, in such a conventional transmissive liquid crystal display device, the brightness of the illumination by the backlight 103 for ensuring the brightness of the screen is substantially constant. , There were the following problems.

That is, the transmissive liquid crystal display device having the backlight 103 is advantageous in terms of contrast and visibility as compared with the reflective liquid crystal display device as described above, but it is preferable to use ambient light (outside light). When the light is strong, the visibility becomes extremely poor. Under ambient light (external light) of a certain intensity or more, the contrast is lower than that of the reflective liquid crystal display device, and the visibility is significantly reduced. In order to
The superiority of visibility is reversed from that of the reflective liquid crystal display device.

As described above, the fluctuation of the condition of the ambient light (external light) greatly affects the visibility of the liquid crystal display surface. Therefore, in a transmissive liquid crystal display device having a backlight, the ambient brightness is generally considered. By adjusting the light transmission amount of the liquid crystal cell and adjusting the brightness (BRIGHT) at any time according to the above, the display screen of the liquid crystal display panel 102 can be easily seen without being affected by the ambient brightness. In order to obtain a display screen that is easy to see even when the ambient light (external light) is extremely strong, the backlight is increased by increasing the light amount of the light source of the backlight 103 so as not to lose the brightness of the ambient light (external light). It is conceivable to increase the brightness of 103.

However, increasing the light amount of the light source by, for example, changing to a light source of higher illuminance or increasing the amount of electricity supplied to the light source of the backlight 103 causes an increase in power consumption, A new problem arises in that the low power consumption, which is a feature of liquid crystal display devices, cannot be utilized.

[Object] In view of the above problems, it is an object of the present invention to provide a liquid crystal display device that selectively switches the optimum display system in accordance with the ambient brightness.

[0024]

The invention as set forth in claim 1 is, as shown in FIG. 1, a backlight 3 arranged on the back surface of a liquid crystal panel 2 for irradiating the liquid crystal panel 2 from the back surface.
And either the reflection of light incident from the display surface of the liquid crystal panel 2 interposed between the liquid crystal panel 2 and the backlight 3 or the transmission of light emitted from the backlight 3. A reflection / transmission selection member 4 that performs an operation, a light detection unit 5 that detects the amount of external light applied to the liquid crystal panel 2, and the reflection / transmission selection based on the amount of light detected by the light detection unit 5. The above object is achieved by including the switching means 6 for selectively switching the reflection or transmission operation of the member 4.

In this case, in order to selectively switch the optimum display method for the above purpose, for example, as described in claim 2, the switching means 6 stores the threshold value storing a preset threshold value. And a comparison unit 8 that compares the threshold value stored in the threshold value storage unit 7 with the light amount detected by the light detection unit 5, and the back level based on the threshold value corresponding to the comparison result of the comparison unit 8. It is effective to include an on / off control unit 9 that controls turning on and off of the light 3.

In addition to the invention described in claim 2, as described in claim 3, the backlight 3 is provided.
Preferably has a fluorescent lamp as a light source, and the reflection / transmission selecting member 4 is preferably a half mirror provided on the irradiation surface of the fluorescent lamp. Further, in addition to the invention described in claim 2, As described in claim 4, the backlight 2 includes a fluorescent lamp as a light source, and a light guide plate that guides the light emitted from the fluorescent lamp to the back surface of the liquid crystal panel.
It has a diffusion plate provided on the front surface of the light guide plate and a reflection plate arranged on the back surface of the light guide plate, and the reflection / transmission selection member 4 is a half mirror provided on the front surface of the diffusion plate. It is preferable.

[0027]

According to the first aspect of the present invention, in the liquid crystal display device in which the reflection / transmission selection member switches to the reflection type or the transmission type liquid crystal display system, the ambient light (external (The amount of light) is detected, and the operation state of the reflection / transmission selection member is switched based on the amount of light detected by the light detection unit by the switching unit, so that it corresponds to the brightness of ambient light (external light). The liquid crystal display system can be switched to a reflective type or a transmissive type.

That is, the optimum display system is selectively switched according to the ambient brightness.

In this case, according to the invention of claim 2,
As the switching unit, the threshold value stored in the threshold value storage unit by the comparison unit is compared with the light amount detected by the light detection unit, and based on the threshold value corresponding to the comparison result,
The ON / OFF control unit controls the lighting and extinguishing of the backlight, and the display system is switched as a transmissive liquid crystal display device when the backlight is turned on and as a reflective liquid crystal display device when the backlight is turned off.

In addition to the invention described in claim 2, even in the case of a direct type backlight as in the invention described in claim 3, in addition to the invention described in claim 2, the invention described in claim 4 Even if it is a side light type backlight as described above.

[0031]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to FIGS.
Will be described with reference to. 2 and 3, in FIG.
The same reference numerals are given to the same portions as.

First, the configuration of this embodiment will be described.

FIG. 2 is a schematic view showing the structure of the main part of this embodiment. In FIG. 2, the liquid crystal display device 1 comprises a liquid crystal panel 2, a backlight 3, a reflection / transmission selection member 4, a light detection means 5, and a switching means 6. In particular, the switching means 6 is a ROM 7 which is a threshold value storage section. A comparator 8, which is a comparison unit,
It is composed of an on / off control unit 9.

The liquid crystal panel 2 is composed of polarizing plates 21 and 22 and glass substrates 23 and 24.
The liquid crystal display is driven by applying a predetermined voltage to various electrodes such as a scanning electrode, a data electrode, and a transparent electrode for a liquid crystal cell formed between them. As shown, an anisotropic conductive film (ACF) 11 is used to form the glass substrate 23, the printed wiring board 12 and the TA.
B (Tape Automated Bonding) Mounted driver LS
It is connected to an I (Large Scale Integrated circuit) 13 and is bent and mounted.

The backlight 3 is composed of a fluorescent lamp 31, a light box 32, and a diffusion plate 33. The fluorescent lamp 31 is arranged at the rear surface of the liquid crystal panel 2.
It is a direct type backlight consisting of a cold cathode lamp,
The light box 32 irradiates the end surface of the light guide plate 23 with light. Also, the light box 32
The inside of the fluorescent lamp 31 is mirror-finished so that the light is reflected, and the light emitted from the fluorescent lamp 31 is efficiently emitted to the front surface.

The diffusion plate 33 is composed of a white acrylic plate and diffuses the light emitted from the fluorescent lamp 31 to balance the brightness.

The reflection / transmission selection member 4 is composed of a half mirror, and when the backlight 3 is turned on, the light from the backlight 3 is transmitted and the back surface of the liquid crystal panel 2 is irradiated with the light, and the backlight 3 is turned off. At times, it reflects light incident from the surface of the liquid crystal panel 2, and the backlight 3
The liquid crystal display system is switched to the backlight transmissive type or the reflective type by turning on or off.

The photodetection section 5 comprises a phototransistor 51 provided on the display surface of the liquid crystal panel 2 and an A / D converter 52 for converting an analog signal output from the phototransistor 51 into a digital signal. There is.

As described above, the switching means 6 is a ROM.
7, a comparator 8 and an on / off controller 9, and the ROM 7 stores threshold value data serving as a comparison reference value of the comparator 8.

The comparator 8 compares the threshold value data stored in the ROM 7 with the output value of the A / D converter 52,
The comparison result is output to the on / off control unit 9. Specifically, when the output value of the A / D converter 52 is larger than the threshold data, “H” is output and the A / D conversion is performed. Bowl 5
When the output value of 2 is less than or equal to the threshold value data, "L" is output.

The on / off control unit 9 is composed of a CPU 91 and a voltage source 92, and the CPU 91 controls the output voltage output from the voltage source 92 based on the output signal output from the comparator 8. Yes, voltage source 92
Is for applying a power supply voltage to the fluorescent lamp 31, which is the light source of the backlight 3.

That is, when the output from the comparator 8 is "L", the power source voltage is applied from the voltage source 92 to the light source 31 by the CPU 91, so that the backlight 3 is in the lighting state and the output from the comparator. Is "H", the CPU 91 causes the voltage source 92
Then, the application of the power supply voltage to the light source 31 is stopped, so that the backlight 3 is turned off.

Next, the operation (action) of this embodiment will be described.

First, the switching operation of the switching means 6 shown in FIG. 2 will be described with reference to FIG.

FIG. 3 is a flow chart for explaining the switching operation of the display system of this embodiment.

First, as the initial liquid crystal display system, a transmissive display system using the backlight 3 in which the backlight 3 is lit is selected (step S1).

Next, ambient light (external light) with respect to the liquid crystal display surface is detected by the phototransistor 51 provided near the display surface of the liquid crystal panel 2 (step S2), and an electric signal corresponding to the detected light amount is A / It is converted into a digital signal by the D converter 52 (step S3).

The digital signal corresponding to the converted amount of ambient light (external light), that is, the output value of the A / D converter 52 is compared with the threshold data stored in the ROM 7, and this A / D converter is compared. When the output value of 52 is larger than the threshold data, “H” is output from the comparator 8 and A /
When the output value of the D converter 52 is less than or equal to the threshold data, "L" is output from the comparator 8 (step S4).

Next, the output from the comparator 8 is "H".
Is checked (step S5), and if the output of the comparator 8 is “L”, that is, if the ambient light (external light) is darker than a predetermined brightness, the on / off control unit 9 determines A voltage is applied to the fluorescent lamp 31, which is the light source of the backlight 3, the backlight 3 is turned on, and the transmissive display method by the backlight 3 is selected as the liquid crystal display method (step S6). (By the way,
In this case, the transmissive display method by the backlight 3 remains selected) On the other hand, in the process of step S5, when the output of the comparator 8 is "H",
That is, when the ambient light (external light) is brighter than the predetermined brightness, the ON / OFF control unit 9 stops the voltage application to the fluorescent lamp 31 which is the light source of the backlight 3, and the backlight 3 is turned off. A reflective display method is selected as the liquid crystal display method (step S7).

Then, by the processing of step S5,
After either step S6 or step S7 is executed, the processing from step S2 to step S5 is repeatedly executed.

By the above switching operation, the display device in the liquid crystal display device is switched according to the brightness of the external light which changes with time.

That is, in this embodiment, in the liquid crystal display device 1 in which the reflection / transmission selection member 4 switches to the reflection type or the transmission type liquid crystal display system, the light detecting means 5 is used.
By detecting the amount of ambient light (external light) applied to the liquid crystal panel 2 by means of the switching means 6, the switching means 6 switches the operating state of the reflection / transmission selection member 4 based on the amount of light detected by the light detection means 5. The liquid crystal display system can be switched to a reflective type or a transmissive type according to the brightness of ambient light (external light).

Therefore, the optimum display system can be selectively switched according to the ambient brightness.

Another preferred embodiment of the present invention will be described below with reference to FIG.
Will be described with reference to. In FIG. 4, the same parts as those in FIG. 2 are designated by the same reference numerals.

In the above-described embodiment, the case where the direct type backlight 3 is used has been described as an example, but in the present embodiment, the present invention is applied to the liquid crystal display device 1 using the sidelight type backlight 3. It is an example when applied.

In the liquid crystal panel 2 in this embodiment, as shown in FIG.
As shown in FIG. 7, the anisotropic conductive rubber 14 is used to connect and mount the glass substrate 23 and the printed wiring board 12 on which the driver LSI 13 is mounted. In addition,
In FIG. 4, reference numeral 15 is bepiru.

The backlight 3 includes a fluorescent lamp 31, a lamp holder 32 ', a diffusion plate 33, a light guide plate 34, and a reflection plate 35.
The fluorescent lamp 31 is composed of a cold cathode FL lamp arranged at the end of the light guide plate 34, and irradiates the end surface position of the light guide plate 34 with light by the lamp holder 32 ′. Further, the lamp holder 32 'is mirror-finished so that the light is reflected inside the lamp holder 32', and is configured to efficiently irradiate the light emitted from the fluorescent lamp 31 in one direction.

When the light guided by the light guide plate 34 is applied to the liquid crystal panel 2, the diffusion plate 33 diffuses the light to balance the brightness, and the light guide plate 34 is a transparent acrylic plate. And guides the light entering from the end face to the back face of the liquid crystal panel 2, and the back face thereof is printed with a halftone dot-like pattern as in the conventional example described above. The amount of light emitted from the part is adjusted.

The reflection plate 35 prevents the light entering the light guide plate 34 from passing through the back surface of the light guide plate 34 and going out.

That is, in the present embodiment, even in the liquid crystal display device having the side light type backlight 3, the display method can be switched in the same manner as in the above-described embodiments.

Although the invention made by the present inventor has been specifically described based on the preferred embodiments, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the scope of the invention. Needless to say. For example, the photo-detecting means 5 in this embodiment includes a phototransistor 51 and an A / D converter 52, but instead of the phototransistor 51, a photothyristor, a photoconductor, a CCD (Charge Coupled Devic).
e) etc. may be used.

Similarly, the fluorescent lamp 31 serving as the light source of the backlight 3 is composed of a cold cathode tube (cold cathode FL lamp), but a fluorescent lamp using a hot cathode tube may be used. .

[0063]

According to the first aspect of the invention, in the liquid crystal display device in which the reflection / transmission selection member switches the liquid crystal display mode to the reflection type or the transmission type, the ambient light (external The liquid crystal corresponding to the brightness of ambient light (external light) by detecting the amount of light) and switching the operating state of the reflection / transmission selection member based on the amount of light detected by the light detection unit by the switching unit. The display system can be switched to a reflective type or a transmissive type.

Therefore, the optimum display system can be selectively switched according to the ambient brightness.

In this case, according to the second aspect of the present invention, the threshold value stored in the threshold value storage section by the comparison section and the light amount detected by the light detection section are compared as the switching means, and the comparison result is obtained. By controlling the turning on and off of the backlight by the on / off control unit based on the threshold value corresponding to, a display system is used as a transmissive liquid crystal display device when turned on and as a reflective liquid crystal display device when turned off. It can be switched.

Further, according to the inventions of claims 3 and 4, in addition to the invention of claim 2, the backlight may be of a direct type or a sidelight type. The display system can be switched.

[Brief description of drawings]

FIG. 1 is a diagram showing a principle configuration of the present invention.

FIG. 2 is a schematic diagram showing a main configuration of the present embodiment.

FIG. 3 is a flowchart illustrating a display system switching operation brightness adjustment process according to the present exemplary embodiment.

FIG. 4 is a schematic view showing a configuration of a main part of another embodiment.

FIG. 5 is an external view of a conventional liquid crystal display device.

FIG. 6 is a schematic sectional view showing an example of a conventional backlight system.

FIG. 7 is a cross-sectional view of a liquid crystal module including a conventional sidelight type backlight.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Liquid crystal display device 2 Liquid crystal panel 3 Backlight 4 Reflection / transmission selection member 5 Light detection means 6 Switching means 7 ROM (threshold value storage section) 8 Comparator (comparison section) 9 On / off control section 11 Anisotropic conductive film 12 Printing Wiring board 13 Driver LSI 14 Anisotropic conductive rubber 15 Bepil 21,22 Polarizing plate 23,24 Glass substrate 31 Fluorescent lamp 32 Light box 32 'Lamp holder 33 Diffusing plate 34 Light guide plate 35 Reflecting plate 51 Phototransistor 52 A / D conversion Device 91 CPU 92 Voltage source 101 Liquid crystal display device 102 Liquid crystal panel 103 Backlight 104, 105 Polarizing plate 106, 107 Glass substrate 110 Fluorescent lamp 111 Light box 112 Light guide plate 113 Reflector 114 Diffuser

Claims (4)

[Claims] 1. A backlight disposed on the back surface of a liquid crystal panel for irradiating the liquid crystal panel from the back surface, and a light intervening between the liquid crystal panel and the backlight, which is incident from a display surface of the liquid crystal panel. A reflection / transmission selection member that performs either reflection or transmission of light emitted from the backlight; light detection means for detecting the amount of external light emitted to the liquid crystal panel; A liquid crystal display device, comprising: a switching unit that selectively switches the reflection or transmission operation of the reflection / transmission selection member based on the amount of light detected by the detection unit. 2. The switching means includes a threshold value storage section for storing a preset threshold value, and a comparison section for comparing the threshold value stored in the threshold value storage section with the light amount detected by the light detection section. The liquid crystal display device according to claim 1, further comprising: an on / off control unit that controls turning on and off of the backlight based on a threshold value corresponding to a comparison result of the comparison unit. 3. The backlight has a fluorescent lamp as a light source, and the reflection / transmission selecting member is a half mirror provided on an irradiation surface of the fluorescent lamp.
The described liquid crystal display device. 4. The backlight comprises a fluorescent lamp as a light source, a light guide plate for guiding the light emitted from the fluorescent lamp to the back surface of the liquid crystal panel, a diffusion plate provided on the surface of the light guide plate, and a light guide plate for guiding the light. The liquid crystal display device according to claim 2, further comprising: a reflection plate disposed on the back surface of the light plate, wherein the reflection / transmission selection member is a half mirror provided on the front surface of the diffusion plate.