JPH10239659A - Back light control system and liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a back light control system and a liquid crystal display device which improve the uniformity of luminance. SOLUTION: A CPU 1 takes in a scanning position detected by a scanning position detection part 3 and reads out a corresponding luminance control value from a ROM 2 in accordance with this detected scanning position to set it to a luminance control value register 5. A luminance control generation part 6 reads out the luminance control value from the luminance control value register 5 and supplies it to a cathode-ray tube constituting a back light 8 through a back light luminance adjustment part 7, and the luminance of emitted light is controlled for one scanning period or plural scanning periods. A luminance difference on an illuminated face which is brought about by the distance from the cathode-ray tube to a light diffusion plate and the difference in angle of incidence is calculated or measured, and the luminance control value to be corrected based on this luminance difference is obtained in each scanning line, and therefore, the luminance on an LCD screen is made uniform by correction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a backlight control system and a liquid crystal display, and more particularly, to a liquid crystal display (LC).
The present invention relates to a backlight control method for controlling the luminance of a backlight used in D) and a liquid crystal display device.

[0002]

2. Description of the Related Art In a conventional backlight of a liquid crystal display device, an attempt is made to achieve a uniform illumination surface by using a cathode tube and a light diffusion plate (or a light guide plate). There is a method to put in. In the case of a backlight requiring a large screen or high brightness, a method of placing a cathode tube directly below a light diffusion plate is generally used.

In addition, various backlight control methods and liquid crystal display devices for controlling the luminance of the backlight have been proposed (Japanese Patent Application Laid-Open Nos. 5-127626 and 3).
198,026).

FIG. 3 is a block diagram showing an example of a conventional backlight control system described in Japanese Patent Application Laid-Open No. 5-127626. In this conventional method, a backlight circuit including a backlight 8, a brightness control unit 12, and a backlight drive unit 13, a display control unit 14, and an LCD drive unit 1
5 and an LCD display unit 16 comprising:
It comprises a synchronizing unit 17 that extracts an LCD driving cycle from the CD drive unit 15 and sends out a synchronizing signal to the luminance control unit 12.

[0005] The LCD display section 16 performs character display. At this time, the LCD drive section 15 alternately drives the individual display elements of the LCD display section 16 at regular intervals to perform dynamic display. On the other hand, the synchronization unit 17
Extracts the LCD drive cycle from the LCD drive unit 15,
The synchronization signal is sent to the brightness control unit 12. Brightness control unit 12
Controls the backlight drive unit 13 so that the backlight 8 is intermittently turned on, and adjusts the brightness of the backlight 8 by changing the duty of turning on and off in the intermittent lighting.

When adjusting the brightness of the backlight 8, the display drive cycle of the LCD drive section 15 and the intermittent lighting cycle of the backlight 8 are synchronized by a synchronization signal from the synchronization section 17. Thus, the duty of the pulse for luminance control can be changed synchronously within the display timing of each segment, and the luminance of each segment can be uniformly adjusted.

FIG. 4 is a block diagram showing another example of the conventional backlight control system. This conventional backlight control system and liquid crystal display device are the control system described in Japanese Patent Application Laid-Open No. 3-198,026, and store a central processing unit (CPU) 20 for controlling the operation of the system, an operation program of the CPU 20, and the like. Read only memory (ROM) 2
1. Random access memory (RAM) 22 for reading and writing data, display signal generation unit 23 for generating a display signal, display memory 24 for storing data for display,
Backlight control register 25, switch 26, power supply 2
And controls the backlight 8 that illuminates the LCD panel 28 from behind.

[0008] The backlights 8 are arranged in parallel in the horizontal direction.
4 (two shaded areas and one shaded area in FIG. 4), the central area of which is directly connected to the terminal of the power supply 27 and the two shaded areas at both ends. Is connected to the terminal of the power supply 27 via the switch 26. As a result, the central region and the regions at both ends of the backlight 8 are individually flashed and adjusted in luminance, so that only a portion necessary for display can be turned on.

In this conventional method, the CPU 20 determines the display mode of display data and the presence or absence of display data on the screen of the LCD panel 28 corresponding to each divided area of the backlight 8.
The backlight 8 is controlled by setting it in the backlight control register 25 and blinking or changing the brightness for each divided area of the backlight 8. That is, by turning off or lowering the brightness of the divided areas of the backlight 8 that are not used for display and the divided areas of the backlight 8 that correspond to portions where no display data exists on the screen, according to the set display mode. The backlight 8 is controlled. As a result, the backlight 8 corresponding to an area where illumination is unnecessary, that is, a part where there is no display is provided.
The power consumption can be reduced by turning off or turning off the low brightness of the divided areas.

[0010]

However, in the conventional backlight control system and the liquid crystal display device, the system for realizing the uniformity of the illuminating surface by using a cathode tube and a light diffusion plate (or a light guide plate) has been proposed. In the case of a backlight that requires a large screen or high brightness, the method of placing the cathode tube directly under the light diffusion plate is generally used. In some cases, the distance from the cathode-ray tube position to the light diffusion plate cannot be made physically the same, so the light propagation distance differs and the luminance differs. There will be a difference.

Among the conventional backlight control system and liquid crystal display device, the backlight control system and the liquid crystal display device having the configuration shown in FIG. 3 are effective for a small display such as a segment display. In a display device that performs graphic display, the number of pixels is large, the synchronization signal has a considerably high frequency, it is not realistic, and a flat light emitting plate corresponding to each pixel or block is required to secure the luminance uniformity effect. However, since it is difficult to realize a high-luminance and large-sized screen, it is difficult to apply it to a high-luminance and large-screen backlight.

Further, among the conventional backlight control system and liquid crystal display device, in the backlight control system and the liquid crystal display device having the configuration shown in FIG. 4, it is necessary to divide the backlight 8 into regions, and these luminances are reduced. It is difficult to make it constant, and a flat light emitting plate corresponding to each pixel or block is required to secure the luminance uniformity effect, as in the conventional method of FIG. Since it is difficult to realize a large-sized one, it is difficult to apply it to a high-luminance backlight for a large screen.

The present invention has been made in view of the above points,
It is an object of the present invention to provide a backlight control method and a liquid crystal display device that can improve the uniformity of luminance.

Another object of the present invention is to provide a backlight control system and a liquid crystal display device which can be applied to a backlight for a large screen with high luminance.

[0015]

In order to achieve the above-mentioned object, the present invention provides a method of calculating in advance a correlation between a scanning position of a scanning line on a liquid crystal display surface and luminance unevenness of an irradiation surface of a backlight. Storage means for storing a correction control value for ensuring the uniformity of the brightness, detection means for detecting the scanning position of the scanning signal, and correction control read from the storage means in accordance with the scanning position detected by the detection means Control means for controlling the luminance of the backlight according to the value. In addition, the backlight includes a plurality of light sources and a light diffusion plate, and the control unit controls the brightness of the plurality of light sources independently of each other for one scanning time or a plurality of scanning times according to the correction control value.

According to the present invention, the luminance of the backlight is controlled by reading the correction control value calculated and stored in the storage means in advance according to the scanning position.
The brightness of the backlight can be controlled according to the scanning position.

In order to achieve the above object, a liquid crystal display device of the present invention irradiates a backlight to the liquid crystal panel and displays desired display data on the liquid crystal panel. A plurality of light sources whose luminance of emitted light is independently controlled by a signal; a light diffusion plate for diffusing light from the plurality of light sources to irradiate a backlight behind the liquid crystal panel; and a light diffusion plate from the plurality of light sources Beforehand and the difference between the incident angle to the scanning position of the scanning line on the liquid crystal panel and the incident luminance to the light diffusion plate are calculated in advance, and correction based on this is used to ensure the uniformity of the luminance. Storage means for storing a control value for each scanning line, detection means for detecting a scanning position of a scanning signal, and a correction control value read from the storage means in accordance with the scanning position detected by the detection means. Flip and is obtained by a configuration in which a control means for controlling the brightness of a plurality of light sources independently of one another.

According to the present invention, in a liquid crystal display device of a backlight requiring a large screen or high luminance, in which a plurality of light sources are placed immediately below a light diffusing plate, the distance from the plurality of light sources to the light diffusing plate and the liquid crystal panel. The brightness of the plurality of light sources can be controlled so as to correct the difference in the brightness of light incident on the light diffusion plate caused by the difference between the scan line and the incident angle associated with the scanning position.

[0019]

Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing one embodiment of a backlight control system and a liquid crystal display device according to the present invention. As shown in FIG. 1, this embodiment has a CPU 1 that controls reading of a brightness control value and setting of the control value.
A ROM 2 storing a brightness control value or a control program calculated in advance, a scanning position detecting unit 3 for detecting a scanning position of the LCD, and a scanning signal generating unit 4 for generating a scanning signal for controlling the LCD display. A brightness control value register 5 for sequentially setting a brightness control value selected according to the scanning line;
A brightness control generation unit 6 for reading a control value from the brightness control value register 5 and generating a control signal therefrom; a backlight brightness adjustment unit 7 for generating a signal for directly controlling the backlight brightness from the brightness control signal; It is composed of

As shown in FIG. 2, the backlight 8 includes a light diffusing plate 10 disposed immediately below (back surface) of the LCD panel 9 of the liquid crystal display device, and illuminates the back surface of the LCD panel 9 through the light diffusing plate 10. And a plurality of cathode tubes 11. In this embodiment, the luminance difference on the backlight illumination surface caused by the difference between the distance from the cathode tube 11 to the light diffusing plate 10 and the angle of incidence from the cathode tube 11 to the scanning position on the LCD panel 9 is calculated. This is solved by sequentially changing the luminance to make the luminance of the illumination surface uniform.

Here, the brightness control value for brightness correction is determined by the difference between the distance from the cathode tube 11 to the light diffusion plate 10 and the angle of incidence from the cathode tube 11 to the scanning position on the LCD panel 9. The brightness difference is calculated for each cathode tube 11 and
A luminance control value that is calculated or measured in advance for each scanning line and that corrects the luminance based on this is stored in the ROM 2 for each cathode tube 11 and for each scanning line.

Next, the operation of this embodiment will be described. The LCD sequentially updates display data by a conventionally known configuration (not shown) and displays a desired image on the LCD panel 9. A scanning signal for controlling the LCD panel 9 is generated by the scanning signal generator 4. Is done.

This scanning signal is taken in by the scanning position detecting section 3, where the scanning position (position on the LCD screen) to be updated is detected. The CPU 1 captures the scanning position detected by the scanning position detecting unit 3, reads a corresponding luminance control value from the ROM 2 according to the detected scanning position, and sets the luminance control value in the luminance control value register 5.

The brightness control generator 6 receives the scanning signal generated by the scanning signal generator 4 and reads the brightness control value from the brightness control value register 5 at a timing based on the scanning signal. The backlight brightness adjustment unit 7 generates a signal for adjusting the brightness of the cathode tube of the backlight 8 based on the brightness control value input from the brightness control generation unit 6, and outputs the signal to the cathode tube constituting the backlight 8. To supply. The cathode tube is 1
In the case where there are a plurality of tubes as indicated by 1, each cathode tube 11
To control the brightness of the light emitted from them for one scanning time or a plurality of scanning times independently of each other.

Thus, on the illumination surface of the backlight 8, the brightness of the backlight is variably controlled according to the position of the scanning line on the LCD screen. Here, as described above, the brightness control value calculates or measures the brightness difference on the illumination surface caused by the difference between the distance from the cathode tube 11 to the light diffusion plate 10 and the angle of incidence, and corrects the brightness based on this. Since the value is obtained for each scanning line, it works to increase the luminance when the scanning line passes through a position where the luminance is normally low (for example, the middle of the adjacent cathode tubes 11), and the luminance on the LCD screen is reduced. Correction can be made uniform.

It should be noted that the position where the luminance is low is usually kept as it is,
It is also possible to make the luminance on the LCD screen uniform by lowering the luminance at a position where the luminance is high. Further, the present invention is not limited to the above-described embodiment. For example, other light sources such as electroluminescence (EL) can be used instead of the cathode tube 11. Furthermore, in principle, the number of light sources can be one.

[0027]

As described above, according to the present invention,
The correction control value calculated and stored in the storage means in advance,
The brightness of the backlight is controlled in accordance with the scanning position by reading out and controlling the brightness of the backlight in accordance with the scanning position, so that the brightness on the LCD display screen can be made uniform.

Further, according to the present invention, in a backlight liquid crystal display device requiring a large screen or high luminance in which a plurality of light sources are placed immediately below a light diffusion plate, the distance from the plurality of light sources to the light diffusion plate is reduced. And, since the brightness of a plurality of light sources is controlled so as to correct the difference in incidence brightness to the light diffusion plate caused by the difference between the angle of incidence of the scanning line on the scanning position and the scanning position in the liquid crystal panel, the cathode tube is used as the light source. It is possible to correct uneven brightness of the directly installed backlight used.

[Brief description of the drawings]

FIG. 1 is a block diagram of an embodiment of the present invention.

FIG. 2 is an explanatory view of the arrangement of the backlight in FIG. 1;

FIG. 3 is a block diagram of an example of the related art.

FIG. 4 is a block diagram of another example of the related art.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Central processing unit (CPU) 2 Read-only memory (ROM) 3 Scanning position detector 4 Scan signal generator 5 Brightness control value register 6 Brightness control generator 7 Backlight brightness adjuster 8 Backlight 9 LCD panel 10 Light Diffusion plate 11 Cathode tube

Claims (3)

[Claims] 1. A correction control value for ensuring uniformity of luminance calculated in advance based on data of a correlation between a scanning position of a scanning line on a liquid crystal display surface and luminance unevenness on an irradiation surface of a backlight. Storage means; detection means for detecting a scanning position of a scanning signal; control for controlling the brightness of the backlight in accordance with the correction control value read from the storage means in accordance with the scanning position detected by the detection means Means for controlling a backlight. 2. The backlight comprises a plurality of light sources and a light diffusing plate, and the control means controls the brightness of the plurality of light sources independently of each other according to the correction control value during one scanning time or a plurality of scanning times. 2. The backlight control method according to claim 1, wherein the control is performed during a period. 3. A liquid crystal display device that irradiates a backlight to a liquid crystal panel and displays desired display data on the liquid crystal panel, wherein a plurality of light sources whose output light luminances are independently controlled by an external control signal. A light source, a light diffusion plate that diffuses light from the plurality of light sources and irradiates the backlight as the backlight behind the liquid crystal panel, a distance from the plurality of light sources to the light diffusion plate, and a scanning line in the liquid crystal panel. The difference in the incident luminance to the light diffuser caused by the difference between the incident angle and the scanning position is calculated in advance, and the correction control value for ensuring the uniformity of the luminance is stored for each scanning line based on the difference. Storage means; detection means for detecting a scanning position of a scanning signal; and the multiple control means read out from the storage means in accordance with the scanning position detected by the detection means. The liquid crystal display device characterized by having a light source intensity control means for each controlled independently of each other.