JPH0495921A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To uniformize the brightness on the entire display screen by controlling the ON-OFF time of a liquid crystal picture element at a place where brightness is low when a sensor detects the place, and then increasing the brightness and making a decrease in brightness at places where brightness is high. CONSTITUTION:The light which is emitted by a fluorescent tube 1 which is arranged horizontally on the back surface of liquid crystal is made incident directly on a diffusion plate 4 or reflected by a reflecting plate 2 arranged behind the fluorescent tube 1 and made incident on the liquid crystal 5. Since the fluorescent tube is arranged horizontally, the horizontal brightness distribution becomes uniform. Further, plural detection sensors 3a are arranged vertically so as to the brightness distribution from the diffusion plate 4, the quantity of deviation from the minimum value of the brightness distribution is calculated, line by line, from output values of the respective sensors 3a, and the H level width of display data on a scanning line is controlled according to the calculated value. Consequently, the brightness distribution on the surface of the liquid crystal becomes uniform in the horizontal and vertical directions.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a transmissive flat liquid crystal display device having a fluorescent tube backlight, and particularly to a liquid crystal display device suitable for reducing brightness unevenness on a display screen. Pause.

[Conventional technology]

Conventionally, in transmissive flat liquid crystal displays that use fluorescent tubes as backlights, it is necessary to uniformly diffuse light from the backlights onto the display screen. For example, in the light curtain method, a fluorescent tube is placed on the back of a liquid crystal display (hereinafter abbreviated as LCD), and a sheet (light curtain) in which a diffuser plate and an AI reflective layer are vapor-deposited in the form of a mesh is provided in between. The light is multiple-reflected between the A1 reflector plate installed behind the fluorescent tube and the light is made uniform. In addition, in the light guide method, a fluorescent tube is placed at the site (side) of the LCD, and a diffuser plate and a light guide placed close to the fluorescent tube are provided on the back of the LCD, so that the light incident on the light guide is
There was one that was designed to be bent uniformly toward the CD.

Incidentally, as a mistake in the prior art, for example, JP-A-61
-25193, JP-A-61-25194, JP-A-6
1-25195, JP-A-61-123883, JP-A-63-5590, JP-A-61-156097, etc.

[Problem to be solved by the invention]

The above-mentioned conventional technology does not have all of the following elements: uniformity of luminance distribution within the screen, efficient incidence of light into the screen, and weight reduction.

That is, in the light curtain method, fluorescent tubes are placed on the back of the LCD, and the light curtain, which is a light reflecting element, is lightweight, so it is superior in terms of high incident efficiency and weight.
There are problems in that the precision of assembling the fluorescent tubes and the light curtain is severe, and the uniformity of brightness is poor. Although the light guide method is advantageous in terms of uniformity of brightness distribution, it has problems such as poor incidence efficiency and heavy light guide.

SUMMARY OF THE INVENTION An object of the present invention is to provide a transmissive flat liquid crystal display device that has a luminance distribution uniformity on the screen equivalent to that of a light guide method and has a high-luminance and lightweight fluorescent tube backlight.

[Means to solve the problem]

The above purpose is to maintain high brightness by placing fluorescent tubes on the back of the liquid crystal part, and by placing multiple brightness detection sensors between the liquid crystal part and the backlight, and to output output from the brightness detection sensors to the liquid crystal drive circuit. This is achieved by adding a circuit that controls the on/off time of the liquid crystal depending on the amount of brightness.

[Effect]

The brightness of a liquid crystal pixel changes depending on the on/off time of the pixel, so when the sensor detects an area with low brightness, it controls the on/off time of the liquid crystal pixel in that area to increase the brightness and increase the brightness. On the contrary, the area is lowered to achieve uniform brightness across the entire display screen.

〔Example〕

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings, taking as an example a case where three fluorescent tube backlights and a progressive scanning type liquid crystal display are used.

FIGS. 1(a) and 1(b) are a rear view and a sectional view of a transmissive flat liquid crystal display having a fluorescent tube backlight according to an embodiment of the present invention. 1 is a fluorescent tube (3 pieces), 2 is a reflector that reflects the light emitted from the fluorescent tube, 3 is a brightness detection sensor board on which brightness detection sensors 3a (9 pieces) are mounted at specific intervals, 4 is a light It is a diffuser plate for dispersing the light, and the fluorescent tube 12 is exposed to the rear side 2. The diffuser plate 4 constitutes a backlight. 5 is a transmissive liquid crystal display. XI indicates the position of the diffuser plate surface, and X2 indicates the position of the liquid crystal screen surface.

In the liquid crystal display device configured as described above, the light emitted from the fluorescent tubes 1 arranged horizontally on the back of the liquid crystal is transmitted directly to the diffuser plate 4 or to the reflecting plate 2 arranged after the fluorescent tubes 1.
The light is reflected by the light and enters the liquid crystal 5. By arranging the fluorescent tubes horizontally, the horizontal brightness distribution becomes uniform. On the other hand, although the luminance distribution in the vertical direction varies, the luminance is averaged to some extent by the diffuser plate, and then the light enters the liquid crystal section.

In data display on the liquid crystal section, scanning is performed in the horizontal direction, and when one line of scanning is completed, the same scanning is performed in the horizontal direction with a one-dot shift in the vertical direction. This operation is repeated, and when all lines have been scanned, the process returns to the first line and resumes scanning. During scanning, the display clock is counted and the count value indicates the display point in the horizontal direction. When the display data input to the liquid crystal at that time is at H level, the display point is turned on and the light from the backlight is transmitted. The pulse width of the H level corresponds to the ON time of the display point, that is, the amount of light transmitted.

A plurality of brightness detection sensors 3a are arranged in the vertical direction so as to detect the brightness distribution from the diffuser plate 4.
The amount of deviation from the minimum value of the brightness distribution is calculated for each line based on the output of a, and the H level width of the display data of the scanned line is controlled from the calculated value. With this control, the brightness on the surface of the liquid crystal remains constant regardless of variations in the brightness incident on the liquid crystal, and the brightness distribution on the surface of the liquid crystal in the horizontal direction.
It becomes uniform in both the vertical direction.

FIG. 2 is a block diagram of a circuit that controls the liquid crystal from detecting brightness. The brightness sensor 3a detects the amount of brightness at a specific position in the Y direction at the X1 position and converts it into an electrical signal.

The deviation amount calculator 7 calculates the brightness deviation of light incident on the liquid crystal display from the input signals from each brightness sensor.

Y on the LCD display inputted from the counter 8
A luminance deviation amount corresponding to the scanning position in the direction is output to the delay circuit 9. The delay circuit 9 delays the display data f and the display clock g by an amount corresponding to the reduction in the on-time of the liquid crystal, which is proportional to the luminance deviation amount.

FIG. 3 shows a timing chart of operation signals. now,
The scanning position of the liquid crystal is the lowest brightness place on the screen (the 5th place).
Assume that the camera is scanning a position (indicated by m in the figure). In this case, the luminance deviation amount output from the deviation amount calculator 7 is I
I□n, and the ON time of the liquid crystal becomes 100%, that is, the delay amount of the delay circuit 9 becomes "0". In other words, this is the timing of the corrected data 3J in FIG. Post-correction data 3J
The time width of the H level is the same for 3h of display data, and the on time of the liquid crystal is 100% for 3h of display data.
becomes.

Next, the scanning position of the liquid crystal is a place where the brightness is 25% higher than the lowest brightness place on the screen (position m in Figure 5).
Assume that you are scanning.

In this case, the luminance deviation amount output from the deviation amount calculator 7 is 25%, and the ON time of the liquid crystal is 75%, that is, the delay amount of the delay circuit 9 is 25% with respect to the display clock. At this time, a clear signal is output from the clear signal generating circuit 11 in FIG. 2 at the timing of the clear signal 3b in FIG. 3, the flip-flop 10 is cleared, and the corrected data J, which is the output of the flip-flop, is This is the timing of corrected data 3J' in the figure. In other words, the corrected data a
= l has an H level time width of 7 for display data 3R.
5%, and the on time of the liquid crystal is 75% of the time when the brightness is lowest.

By repeating these controls, the liquid crystal on-time control as shown in FIG. 5 is performed for the luminance distribution on the surface of the diffuser plate as shown in FIG. As a result, the luminance distribution of the liquid crystal screen display becomes uniform as shown in FIG.

〔Effect of the invention〕

According to the present invention, since the fluorescent tube can be placed on the back side of the liquid crystal display, the light emitted from the fluorescent tube can be efficiently incident on the liquid crystal, and a high-brightness display screen can be obtained. Conversely, if the brightness is set to the same level as the light guide method, it can be driven with low power consumption.

Furthermore, since variations in brightness can be detected and corrected to make them uniform, brightness uniformity equivalent to that of the light guide method can be obtained, and a high-quality screen can be provided.

Furthermore, since heavy parts such as a light guide are not required, weight reduction can be achieved.

Furthermore, since the positional accuracy of the phosphor, liquid crystal display, and brightness detection sensor is not severe, it is easy to assemble.

[Brief explanation of drawings]

FIG. 1(a) is a rear view of a liquid crystal display device according to an embodiment of the present invention, and FIG. 1(b) is a rear view of a liquid crystal display device according to an embodiment of the present invention.
A II line sectional view, FIG. 2 is FIG. 1(a). (b) is a configuration diagram of the control circuit of the liquid crystal display device, FIG. 3 is an operation signal timing chart of each part of the control circuit in FIG. 2, FIG. 4 is a luminance distribution graph on the surface of the diffuser plate in FIG. The figure is a characteristic diagram of the on-time control of the display signal of the liquid crystal based on the operation shown in FIG. 3, and FIG. 6 is a graph of the luminance distribution on the surface of the liquid crystal screen shown in FIG. DESCRIPTION OF SYMBOLS 1... Fluorescent tube, 2... Reflection plate, 3a... Brightness detection sensor, 4... Diffusion plate, 5... Liquid crystal. Figure 1

Claims (1)

[Claims] 1. In a transmissive flat liquid crystal display device with a fluorescent tube backlight, a sensor detects variations in the brightness of the backlight, and the on/off time of the liquid crystal is controlled according to the detection signal of the sensor to reduce the brightness of the display screen. A liquid crystal display device comprising: a control circuit for controlling the display;