JPH06331962A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To obtain optimum luminance corresponding to the brightness of the circumference by detecting the quantity of external light irradiating a liquid crystal panel and adjusting the luminance of a backlight based on the quantity of the external light. CONSTITUTION:This liquid crystal display device 1 is constituted of the liquid crystal panel 2, the backlight 3, a photodetector means 4, and a luminance adjusting means 5; and the adjusting means 5 consists of a ROM 6 being a threshold storage part, a comparator 7 being a comparison part, and a luminance control part 8. Then, it is provided with the backlight 3 illuminating the back surface of the panel 2. The quantity of the external light irradiating the panel 2 is detected by the means 4, and energizing quantity for a fluorescent lamp which it the light source of the backlight 3 is adjusted based on the quantity of the light detected by the means 4 by the adjusting means 5. Thus, the luminance of the backlight 3 is adjusted corresponding to the quantity of the external light.

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 performs backlight irradiation with an optimum illuminance with respect to 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
Thode Ray Tube), for example, a liquid crystal display device as shown in FIG. 6 has been widely used.

In this liquid crystal display device, a light source is provided on the back surface of the liquid crystal panel in order to provide an easy-to-read screen without being influenced by the ambient brightness, and a so-called backlight is provided to illuminate the liquid crystal panel from the back surface. As a backlight structure, a light source is arranged at the back position of the liquid crystal panel and the liquid crystal panel is directly illuminated from the back side (see FIG. 7A), and a liquid crystal panel is generally used. There is a side light (or edge light) system (refer to FIG. 7B) in which a light source is arranged at a side surface position and the light from the light source is guided to the back surface of the liquid crystal panel to be indirectly irradiated. In FIG. 7, a is a fluorescent lamp, b is a diffusion plate,
c is a light guide plate.

The direct type has high light utilization efficiency and high brightness, but it is low in 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.

The fluorescent lamp used as the light source of the backlight includes a cold cathode tube and a hot cathode tube, and although the hot cathode tube can obtain high brightness, many cold cathode tubes are used in terms of heat generation and life. It is used.

[0007]

2. Description of the Related Art Conventionally, as a liquid crystal display device provided with this type of sidelight type backlight, for example, FIG.
There is a liquid crystal display device 101 as shown in FIG. FIG. 8 is a cross-sectional view of a liquid crystal module including a conventional sidelight type backlight.

As shown in FIG. 8, 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 face to the back face of the liquid crystal panel 102, and a dot pattern is printed on the back face of the light guide plate 112. 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 not coming out, and the diffusion plate 114 is composed of a white acrylic plate or the like. When the light guided by the light guide plate 112 is applied to the liquid crystal panel 102, the light is diffused to balance the brightness.

In the above structure, the light entering from the end surface of the light guide plate 112 is repeatedly reflected in the light guide plate 112 (acrylic plate) due to the difference in refractive index between acrylic and air, and 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 position of the end surface 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.

[0017]

However, in the liquid crystal display device having such a conventional backlight, the backlight 103 for ensuring the brightness of the screen is provided.
Since the brightness of the illumination due to is almost constant, there are problems as described below.

That is, fluctuations in the conditions of ambient light (external light) have a great influence on the visibility of the liquid crystal display surface, and in a transmissive liquid crystal display device, the visibility is high when the ambient light (external light) is strong. Extremely worse.

Specifically, when the brightness of external light is darker on the display surface of the liquid crystal panel 102 than the brightness of the backlight 103, the display screen is dazzling and the displayed contents are difficult to see, and the backlight 103 is also difficult to see. If the brightness due to outside light is too bright as compared with the brightness of, the contrast of the liquid crystal display screen is lowered, and the display screen becomes difficult to see.

Therefore, conventionally, in order to make it easy to see the display surface of the liquid crystal display panel 102 without being influenced by the ambient brightness, the brightness (bright: B
Although the above-mentioned problem has been dealt with by performing the RIGHT) adjustment, for example, when a document is created by a word processor, a personal computer, or the like, the user may forget to adjust the brightness for a long time because the work is so concentrated.

As described above, when the balance between the ambient brightness and the brightness of the display screen is lost, the operator's eyes unnecessarily bear a burden without knowing it, causing eye fatigue and possibly causing a decrease in visual acuity. Come on.

[Object] In view of the above problems, it is an object of the present invention to provide a liquid crystal display screen having an optimum brightness corresponding to the ambient brightness.

[0023]

According to a first aspect of the present invention, as shown in FIG. 1, in a liquid crystal display device 1 having a backlight 3 for illuminating a liquid crystal panel 2 from the back side, the liquid crystal panel 2 is irradiated. By providing the light detecting means 4 for detecting the light quantity of the external light and the brightness adjusting means 5 for adjusting the brightness of the backlight 3 based on the light quantity detected by the light detecting means 4, the above object is achieved. Has achieved.

In this case, in order to obtain the liquid crystal display screen with the optimum brightness which is the above-mentioned object, for example, as described in claim 2, the brightness adjusting means 5 sets a predetermined number of thresholds set in advance. A threshold value storage unit 6 to store, a comparison unit 7 that compares the threshold value stored in the threshold value storage unit 6 with the light amount detected by the light detection unit 4, and a threshold value corresponding to the comparison result of the comparison unit 7. It is effective to include a brightness control unit 8 that controls the brightness of the backlight 3 based on the above.

Then, in addition to the invention described in claim 2, as described in claim 3, the backlight 3
Has a fluorescent lamp as a light source, and the brightness control unit 8
Controls the brightness of the backlight 3 by controlling the amount of electricity supplied to the fluorescent lamp, and, in addition to the invention described in claim 2, the backlight described in claim 4. 3 has a plurality of fluorescent lamps as a light source, and the brightness control section 8 controls the brightness of the backlight 3 by controlling the number of fluorescent lamps to be energized. In addition to the invention described above, the backlight 3 includes a fluorescent lamp as a light source, a light guide plate for guiding light emitted from the fluorescent lamp to the back surface of the liquid crystal panel 2, and the conductive lamp. The brightness control unit 8 has a diffusion plate provided on the front surface of the light plate and a reflection plate arranged on the back surface of the light guide plate, and the brightness control unit 8 controls the amount of reflection by the reflection plate to thereby control the brightness of the backlight 3. Control or In addition to the invention described in Item 2, as described in Item 6, the backlight 3 includes a fluorescent lamp as a light source and a light guide plate that guides light emitted from the fluorescent lamp to the back surface of the liquid crystal panel 2. And 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 brightness control section 8 is formed between the light guide plate and the reflection plate. It is preferable to control the brightness of the backlight 3 by controlling the amount of reflection by the mask.

[0026]

According to the first aspect of the invention, in the liquid crystal display device having the backlight for illuminating the liquid crystal panel from the back side, the light amount of the ambient light (external light) applied to the liquid crystal panel is detected by the light detecting means. At the same time, the brightness of the backlight is adjusted by the brightness adjusting unit based on the amount of light detected by the light detecting unit. Therefore, the brightness of the backlight is adjusted according to the amount of external light.

That is, a liquid crystal display screen having an optimum brightness can be obtained according to the ambient brightness.

In this case, according to the invention of claim 2,
As the brightness adjusting unit, the threshold value stored in the threshold value storing unit is compared by the comparing unit with the light amount detected by the light detecting unit, and the brightness of the backlight is controlled by the brightness controlling unit based on the threshold value corresponding to the comparison result. Therefore, in addition to the invention described in claim 1, the luminance is finely adjusted based on the set threshold value.

According to the inventions of claims 3 to 6, in addition to the invention of claim 2, the brightness of the backlight is controlled by the brightness controller by various means.

[0030]

DETAILED 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. In addition, in FIGS.
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 diagram 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 light detecting means 4, and a brightness adjusting means 5. In particular, the brightness adjusting means 5 is a threshold value storage unit R.
It is composed of an OM 6, a comparator 7 as a comparison unit, and a brightness control unit 8.

The liquid crystal panel 2 is composed of polarizing plates 21 and 22 and glass substrates 23 and 24, and has a finer connection pitch (TAB (Tape) in order to make the liquid crystal panel 2 high-definition and thin, light and compact. A driver LSI (Large Scale Integrated circuit) 25 is directly mounted on the glass substrate 23 of the liquid crystal panel 2 in order to cope with the connection limit pitch of Automated Bonding) and is generally 0.1 mm or less). The liquid crystal cell formed between the glass substrates 23 and 24 is driven by applying a predetermined voltage to various electrodes such as a scanning electrode, a data electrode, and a transparent electrode.

The backlight 3 is composed of a fluorescent lamp 31, a lamp holder 32, a light guide plate 33, a reflection plate 34, and a diffusion plate 35. The fluorescent lamp 31 is a cold cathode arranged at the end of the light guide plate 33. It is composed of an FL lamp, and the lamp holder 32 irradiates the end surface of the light guide plate 33 with light. Further, the lamp holder 32 is formed to reflect light inside thereof, and is configured to efficiently irradiate the light emitted from the fluorescent lamp 31 in one direction.

The light guide plate 33 is made of a transparent acrylic plate and guides the light entering from the end face to the back face of the liquid crystal panel 2. The back face of the light guide plate 33 has a halftone dot pattern similar to the above-mentioned conventional example. Is printed, and the light emission amount of each part is adjusted by the print density of this print pattern.

The reflection plate 34 is for preventing the light entering the light guide plate 33 from passing through the back surface of the light guide plate 33 and going out, and the diffusion plate 35 is used for the light guided by the light guide plate 33. When the liquid crystal panel 2 is irradiated with the light, the light is diffused to balance the brightness.

The photodetector section 4 comprises a phototransistor 41 provided on the display surface of the liquid crystal panel 2 and an A / D converter 42 for converting an analog signal output from the phototransistor 41 into a digital signal. There is.

The brightness adjustment means 5, the _cormorants I mentioned _above, RO
The ROM 6 is composed of an M6, a comparator 7 and a brightness control section 8. The ROM 6 stores a plurality of threshold value data (in this case, nine threshold value data S1 to S9) serving as comparison reference values of the comparator 7. Yes, the comparator 7
The output value of the A / D converter 42 is compared by comparing a plurality of threshold value data stored in the ROM 6 with the output value of the A / D converter 42.
_{The I} remote _large kina minimum threshold _data and outputs it to the brightness control unit 8.

Here, the A / D converter 4 in this embodiment is used.
The relationship between the _second output value C1 -C10 and the threshold data S1 ～S9 shown _in FIG.

In FIG. 3, the output value of the _A / D converter 42 is C
If less than 1, S1 is selected as the threshold data in the comparator _over data 7, the output value of the A / D converter 42 is C1
If the _above, and smaller than C2, the comparator 7
In S2 is selected as threshold _value data, the selected threshold data to the same manner, the output value of the A / D converter 42 is C
In the case of more than 10, as _a in the comparator 7 threshold _data S
9 is selected.

The brightness controller 8 includes a CPU 81 and a current source 8
The CPU 81 includes a current source 82 based on the threshold data S1 to S9 output from the comparator 7.
The current source 82 supplies the power supply current to the fluorescent lamp 31 which is the light source of the backlight 3.

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

First, a brightness adjusting method in the brightness adjusting means 5 shown in FIG. 2 will be described with reference to FIG.

FIG. 4 is a flow chart for explaining the brightness adjustment processing of this embodiment.

When the brightness adjusting process is executed, first, the number N of the threshold data set in the ROM 6 is substituted into the variable N, and the variable i is initialized to null (step S1). ).

Next, the variable i is incremented (step S2), and the threshold data Si and A /
The output value C from the D converter 42 is compared by the comparator 7 (step S3).

Here, the output value C from the A / D converter 42
Is smaller than the threshold data Si, the threshold data Si (i is a variable in this case) is selected as the data D output from the comparator 7 (step S4).

On the other hand, when the output value C from the A / D converter 42 is equal to or larger than the threshold data Si, it is checked whether or not the variable i has reached the variable N (step S5), and the variable i is checked.
If the value of is less than or equal to the value of the variable N, the processes of steps S2 and S3 are executed again, and if the value of the variable i is greater than or equal to the value of the variable N in the process of step S5, output from the comparator 7. The threshold data Sn (in this case, n is the number of threshold data) is selected as the data D to be processed (step S6).

The data D output from the comparator 7 is input to the CPU 81, and the CPU 81 causes the current source 82 to operate.
The power supply current value supplied from the fluorescent lamp 31 to the fluorescent lamp 31 is controlled to be the current value corresponding to the data D (step S
7) Based on this current value, a predetermined amount of light is emitted from the fluorescent lamp 31.

Hereinafter, the light emitted from the fluorescent lamp 31 is applied to the back surface of the liquid crystal panel 2 by the light guide plate 33, the reflection plate 34, and the diffusion plate 35.

The above brightness adjustment processing is executed at regular time intervals, and brightness adjustment is performed in accordance with the brightness of external light which changes with time.

That is, in the present embodiment, the liquid crystal display device 1 having the backlight 3 for illuminating the liquid crystal panel 2 from the back surface.
In the above, the light detecting means 4 detects the light quantity of the external light applied to the liquid crystal panel 2, and the brightness adjusting means 5 detects the light quantity of the outside light with respect to the fluorescent lamp 31 serving as the light source of the backlight 3. By adjusting the amount of energization, the brightness of the backlight 3 can be adjusted according to the amount of external light.

Therefore, it is possible to obtain a liquid crystal display screen having an optimum brightness corresponding to the brightness of the surroundings, and the brightness of the backlight 3 is adjusted by controlling the energization amount to the fluorescent lamp 31, so that it is fine. Brightness can be adjusted.

Another preferred embodiment of the present invention will be described below with reference to FIG.
Will be described with reference to. In FIG. 5, the same parts as those in FIG. 2 are designated by the same reference numerals.

In this embodiment, a plurality of (three in this case) fluorescent lamps 31a, 31 are used as the light source of the backlight 3.
b, 31c, and the fluorescent lamps 31a, 31b, 3
Corresponding to the number of 1c, in which the current source 82a is controlled by the CPU81 on _{Brightness control} section within 8, 82b, a 82c provided. In this case, two pieces of threshold value data S11 and S12 are stored in the ROM 6, and the comparator 7 stores the plurality of threshold value data S and A stored in the ROM 6.
By comparing the output value D of the / D converter 42,
/ Than the output value C of the D converter 42 and outputs a large minimum threshold _data to the brightness control unit 8.

That is, the output value _D from the comparator 7
If There smaller than the threshold value _data S11, CPU 81 causes the lights only fluorescent lamps 31a using current sources 82a,
If the output value D from the comparator 7 is also small _Ri S12 good the threshold data S11 above, CPU 81 is the fluorescent lamp 31a using current sources 82a and current source 82b, 31b is lit, the output value D from the comparator 7 Threshold data S
When it is 12 or more, the CPU 81 determines that the current sources 82a, 82
b, 82c using all fluorescent lamps 31a, 31
Turn on b and 31c.

Therefore, in this embodiment, the liquid crystal panel 2
In the liquid crystal display device 1 provided with the backlight 3 that illuminates the back surface of the liquid crystal panel 1, the light detection unit 4 detects the amount of external light applied to the liquid crystal panel 2, and the brightness adjustment unit 5
The plurality of fluorescent lamps 31a, 31 serving as the light source of the backlight 3 based on the amount of light detected by the light detection means 4 by
By selectively energizing b and 31c, the brightness of the backlight 3 can be adjusted according to the amount of external light.

[0058] In the foregoing, the invention made by the inventors has been concretely described based on preferred _actual施例, the present invention is not limited to the above embodiments, various changes without departing from the scope of the invention It goes without saying that it is possible. For example, the photodetector 4 in this embodiment is composed of a phototransistor 41 and an A / D converter 42, but instead of the phototransistor 41, 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. .

Further, according to the above-described embodiment, as the brightness adjustment, the amount of electricity supplied to the fluorescent lamp 31 serving as the light source of the backlight 3 is changed, or the plurality of fluorescent lamps 31a, 3a.
The brightness of the backlight 3 was changed by providing 1b and 31c and selecting a fluorescent lamp to be energized.
In addition, the brightness is adjusted by controlling the reflection amount of the reflection plate 34, which is one of the components of the backlight 3, or a mask (printing pattern formed between the light guide plate 33 and the reflection plate 34). The brightness may be adjusted by changing (1).

[0061]

According to the first aspect of the invention, in the liquid crystal display device having a backlight for illuminating the liquid crystal panel from the back side, the light detecting unit detects the amount of external light applied to the liquid crystal panel and adjusts the brightness. By adjusting the brightness of the backlight based on the amount of light detected by the light detecting unit by the means, the brightness of the backlight can be adjusted in accordance with the amount of external light.

Therefore, it is possible to obtain the liquid crystal display screen having the optimum brightness corresponding to the ambient brightness.

In this case, in the invention according to the second aspect, as the brightness adjusting means, the threshold value stored in the threshold value storing section by the comparing section is compared with the light amount detected by the light detecting section, and the result is compared. By controlling the brightness of the backlight by the brightness control unit based on the threshold value, it is possible to perform fine brightness adjustment based on the set threshold value, in addition to the invention described in claim 1.

Further, according to the invention described in claims 3 to 6, in addition to the invention described in claim 2, the brightness controller can control the brightness of the backlight by various means.

[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 diagram showing a relationship between an output value of an A / D converter and threshold data in the present embodiment.

FIG. 4 is a flowchart for explaining a brightness adjustment process of the present embodiment.

FIG. 5 is a schematic diagram showing a configuration of a main part of another embodiment.

FIG. 6 is an external view of a conventional liquid crystal display device.

FIG. 7 is a schematic sectional view showing an example of a conventional backlight system.

FIG. 8 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 Back light 4 Light detecting means 5 Brightness adjusting means 6 ROM (threshold storing part) 7 Comparator (comparing part) 8 Brightness controlling part 21, 22 Polarizing plate 23, 24 Glass substrate 25 Driver LSI 31 Fluorescent Lamp 32 Lamp holder 33 Light guide plate 34 Reflector plate 35 Diffuser plate 41 Phototransistor 42 A / D converter 81 CPU 82 Current source 31a, 31b, 31c Fluorescent lamp 82a, 82b, 82c Current source 101 Liquid crystal display device 102 Liquid crystal panel 103 Back Lights 104 and 105 Polarizing plates 106 and 107 Glass substrate 110 Fluorescent lamp 111 Lamp holder 112 Light guide plate 113 Reflector plate 114 Diffuser plate

Claims (6)

[Claims] 1. A liquid crystal display device comprising a backlight for illuminating a liquid crystal panel from the back side, comprising: a light detecting means for detecting the light quantity of external light applied to the liquid crystal panel; and a light quantity detected by the light detecting means. A brightness adjusting unit that adjusts the brightness of the backlight based on the liquid crystal display device. 2. The brightness adjusting means compares a threshold value storage section for storing a predetermined number of threshold values set in advance, with the threshold value stored in the threshold value storage section and the light amount detected by the light detecting means. The liquid crystal display device according to claim 1, further comprising: a comparison unit; and a brightness control unit that controls the brightness 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 brightness control unit controls the brightness of the backlight by controlling the amount of electricity supplied to the fluorescent lamp. Item 2. A liquid crystal display device according to item 2. 4. The backlight has a plurality of fluorescent lamps as a light source, and the brightness control unit controls the brightness of the backlight by controlling the number of fluorescent lamps to be energized. The liquid crystal display device according to claim 2. 5. 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. The reflection plate arranged on the back surface of the light plate, and the brightness control unit controls the brightness of the backlight by controlling the amount of reflection by the reflection plate. Liquid crystal display device. 6. 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. A reflection plate disposed on the back surface of the light plate; and the brightness control unit controls the brightness of the backlight by controlling the amount of reflection by a mask formed between the light guide plate and the reflection plate. The liquid crystal display device according to claim 2, which is controlled.