JPH10282470A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress power consumption in a transmission type liquid crystal display device using a back light. SOLUTION: In the liquid crystal display device using a light emitting diode(LED) corresponding to three primary colors as the back light 10 and displaying an image through a liquid crystal layer 5, the luminance information data of respective pixels in one frame are mutually compared, the luminance values of pixels having the maximum luminance values of the three primary colors in one frame are found out and the light emission luminance of the LED at the time of displaying one frame is set up to the maximum luminance. Thereby the luminance of the back light 10 can be changed in each frame and the power consumption of the LED can be minimized in each frame.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transmission type liquid crystal display device, and more particularly to a light source called a backlight.

[0002]

2. Description of the Related Art Conventionally, in a transmission type liquid crystal display device,
As a backlight, a lamp using a discharge lamp is generally used.However, in addition to a discharge lamp, a proposal has been made to use a light emitting diode, an electroluminescent device, or an organic electroluminescent device for the backlight. Have been. A backlight using the above-described light-emitting diode, electroluminescent element, or organic electroluminescent element has a feature that it can be made smaller than a backlight of a discharge lamp. In particular, in the case of using a light emitting diode or a backlight using an organic electroluminescent element, there is no need to use an inverter in the case of a discharge lamp, and there is an advantage that the size can be reduced accordingly.

[0003]

However, conventionally,
In a transmissive liquid crystal display device, for example, in the case of a 10-inch display device, most of the power consumption is consumed by the backlight. This is the same in the case where a light emitting diode, an electroluminescent element or an organic electroluminescent element is used, regardless of whether a discharge lamp is used.

On the other hand, transmissive liquid crystal display devices are frequently used in notebook personal computers and the like, and in this field, there is a strong demand for long-term use in a battery-driven state. Edited by Nikkei BP, "Separate volume flat panel display 199"
As described in “6”, it is indispensable to reduce the power consumption of the display device in order to meet the above demand.

[0005]

According to the present invention, in order to reduce power consumption in a liquid crystal display device, a liquid crystal display device using light emitting diodes corresponding to three primary colors as a backlight has a luminance of each pixel in one frame. The information is compared to calculate the luminance of the pixel having the maximum luminance of each of the three primary colors in the one frame, and set the light emission luminance of the light emitting diode when displaying the one frame to the maximum luminance. ing. With this configuration, the luminance of the backlight can be changed for each frame, and the power consumption of the light emitting diode can be suppressed to a minimum for each frame.

According to the present invention, there is provided a liquid crystal display device which divides one frame into a plurality of regions and uses light emitting diodes corresponding to three primary colors as backlights corresponding to the plurality of regions. The luminance information of each of the three primary colors in the area is determined by comparing and calculating the luminance information of the three primary colors, and the emission luminance of the light emitting diode when displaying the area is set to the maximum luminance. ing. With this configuration, power consumption can be further reduced as compared with the above case.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a transmission type liquid crystal display device according to an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a sectional view showing the structure of a liquid crystal module according to the present invention. In FIG. 1, reference numeral 1 denotes an output-side polarizing plate;
Reference numeral 2 denotes a glass substrate, 3 denotes a color filter, 4 denotes a transparent electrode, 5 denotes a liquid crystal layer, 6 denotes a transparent electrode, 7 denotes a thin film transistor (TFT) associated with each pixel, 8 denotes a glass substrate, and 9 denotes an incident side polarizing plate. In addition, a liquid crystal panel is composed of the output side polarizing plate 1 and the input side polarizing plate 9. Reference numeral 10 denotes a backlight including a light source and a light guide plate, and 11 denotes a reflection plate.

Next, FIG. 2 is a perspective view of a liquid crystal display device according to the present invention. In FIG. 2, 12 is a liquid crystal panel, 13
Is a backlight including a light source and a light guide plate, 14 is a reflection plate, 15 is a memory and arithmetic circuit for information to be displayed,
16 is a connection to the liquid crystal panel, 17 is a backlight luminance switching circuit, 18 is an information memory and arithmetic circuit 1
5 to the backlight brightness switching circuit 17;
Reference numeral 19 denotes a connection from the backlight luminance switching circuit 17 to the backlight.

(Embodiment 1) First, a color display liquid crystal panel of about 5 inches (twisted nematic mode, display capacity QVGA, with color filter) was prepared by a known method. Next, from Kagoshima Matsushita Electronics Co., Ltd.
As a light emitting diode corresponding to the primary color, that is, red, the product L
N289CUQ as green, LNG389CNJ,
As blue, LNG992CFQ was obtained and used as a backlight.

Next, FIG. 3 shows a perspective view of the backlight according to the present embodiment. In the figure, reference numeral 20 denotes light emitting diodes arranged in a large number in the order of red, green, and blue. 21
Is a light guide plate formed of acryl, which was obtained from Meikaku System Co., Ltd. Reference numeral 22 denotes a large number of protrusions formed on the back surface of the light guide plate, and this distribution is such that light is scattered so that uniform light is emitted upward as indicated by arrows. The above configuration was formed by a printing method. After that,
The circuit block, the reflector and the like were configured as described in FIGS.

In the transmission type liquid crystal display device of the present invention,
Compared with a normal backlight in which the light source is a discharge tube, the configuration does not include an inverter. Also, when a discharge tube (discharge lamp) is used as a backlight, it is difficult for the discharge tube to quickly switch brightness,
When a light emitting diode is used as the light source of the backlight, the luminance can be quickly switched.
The luminance can be switched for less than microsecond. Incidentally, in the display device according to the present embodiment, one horizontal scanning period is 69 microseconds, so that the speed of 1 microsecond is a sufficient speed.

When the light emitting diode is used as a backlight light source as described above, the luminance can be switched quickly, so that the luminance can be switched for each frame of the screen. However, when a discharge lamp is used as the backlight as in the conventional case, it is difficult to switch the luminance for each frame. Therefore, the luminance of the backlight is always lit at the maximum luminance, and an image with a low luminance is displayed. For this purpose, it is necessary to block a certain amount of light by the liquid crystal layer. Therefore, if a discharge lamp is used as a backlight as in the related art, the light is wasted, and the power consumption is increased by the wasted light.

Next, a method of driving the transmission type liquid crystal display device of the present invention when the luminance is switched for each frame using the light emitting diode will be described below.

The feature of the present invention lies in the memory and arithmetic circuit 15 for information to be displayed and the luminance switching circuit 17 for the backlight in FIG. This point will be described with reference to FIG. 4 which is a flowchart of driving performed by these circuits.

First, the maximum achievable luminance of each of red, green, and blue (here, R100, G100,
And B100) are stored.

Each red pixel in one frame to be displayed next,
Display information of each green pixel and each blue pixel (specifically, information on the magnitude of luminance), R (x, y), G (x, y), B
The numerical value of (x, y) is externally transmitted to the memory and the arithmetic circuit 15 of the liquid crystal display device. This R (x, y)
To explain, for example, R (1,2) is (1,
2) indicates information relating to the luminance of the pixel for displaying red given by the coordinates 2). More specifically, for example, if R100 has a luminance of 100 (arbitrary unit), and it is desired to set the display luminance of red to 50 (arbitrary unit) at the coordinates (1,2), this R (1,2) Is recorded as 50%, which is the ratio of the luminance to be actually displayed to the maximum achievable luminance. If the liquid crystal layer is controlled to block 50% of the light emitted from the light source based on this information, (1,
Red display with desired luminance can be performed at the coordinates 2).

Here, in one frame, usually, red, green,
There are a plurality of pixels for displaying blue, and the luminance of each pixel is also different. At the time of the above transmission, the arithmetic circuit 15 compares and calculates the maximum luminance (absolute value) of each color among a plurality of red, green, and blue pixels existing in one frame.
This comparison operation will be described. For example, there are 100 pixels for displaying red, and the 100 red pixels have different luminances such as 30% and 80% as luminance information other than the pixels having the information of 50% as described above. It is assumed that a pixel having information exists. If the maximum value of the 100 pieces of information is 80%, the maximum achievable luminance of red × 80% is determined as the maximum luminance (absolute value). The maximum luminances of red, green, and blue calculated as described above are determined as MAXR, MAXG, and MAXB and stored.

Next, R (x, y), G in the memory 15
Conversion of luminance information (x, y) and B (x, y) is performed. Specifically, as shown in FIG.
The new red, green and blue display signals are represented by R (x, y)
× R100 / MAXR, G (x, y) × G100 / MA
XG, B (x, y) × B100 / MAXB, drive waveforms are calculated according to the calculation, and a voltage is applied to each pixel.

The above calculation will be described in detail below with a concrete example. As in the previous example, for example, R
100 is the luminance of 100 (arbitrary unit), and (1,
When it is desired to set the display luminance of red to 50 (arbitrary unit) at the coordinates of 2), this R (1,2) is 50 which is the ratio of the luminance to be actually displayed to the maximum achievable luminance.
The information of% is recorded. Thereafter, according to the calculation, if the maximum luminance information of red in a specific one frame is 80%, MAXR = 100 (arbitrary unit) × 80% = 80
(Arbitrary unit). Here, R (1,2) × R100
By calculating / MAXR, 50% × 100/80 = 6
2.5%. That is, the luminance information of R (1,2) initially contains information of 50%, but the maximum luminance of red in a specific frame is 10%.
Since it changed from 0 to 80 (all are arbitrary units), R
That is, the luminance information of (1, 2) is linked to these and changed from 50% to 62.5%.

By performing the driving as described above, according to the present invention, the power consumption can be reduced. The reason will be described in detail below.

When a discharge lamp is used as a light source as in the prior art, the luminance of the light source cannot be switched for each frame. Now, for example, the maximum achievable luminance of red is 100
(Arbitrary unit), and in a specific frame, R
Assuming that the maximum value of (x, y) is 80%, even in the red pixel which is desired to emit the brightest light, 20% of the light emitted from the light source must be blocked by the liquid crystal layer, It means that 20% of the light amount of the light source is emitted uselessly.

On the other hand, in the present invention, since a light emitting diode capable of switching the luminance of the light source for each frame is used, for example, the maximum value of R (x, y) in a specific frame is determined. Is 80%, the maximum luminance of the red light emitting diode is 80%.
If the light is illuminated so as to be (arbitrary unit), it is possible to eliminate the waste of 20% of the light amount as in the related art. In fact, in the case of displaying an image of a scenery or the like, the power is reduced to about half as compared with the case where the present invention is not used.

(Embodiment 2) A color display liquid crystal panel of about 10 inches (twisted nematic mode, display capacity VGA, with color filter) was manufactured by a known method. Next, the color display liquid crystal panel section and the backlight section are correspondingly divided and divided into a plurality of N areas.

The backlight in each area is formed as shown in FIG. FIG. 5 is a sectional view showing the configuration of the liquid crystal display element according to the present embodiment. In the figure, 23 is a liquid crystal cell, 24 is an acrylic light guide plate, 25 is a protrusion, and 26 is a light emitting diode group.

The present embodiment is the same as the above-described first embodiment except for the particularity of the position of each light-emitting diode as described above. Also, the driving method of the liquid crystal display device according to the present embodiment is the same as that of the above-described first embodiment. In one frame, the maximum luminance value is extracted from the pixel information to be displayed in each region in each color and in each region. Then, the power supply to the light emitting diode is reduced so that the luminance value is obtained.
A voltage is applied to the liquid crystal so as to increase the transmittance of the liquid crystal. Thus, power consumption can be reduced as in the first embodiment.

However, in the present embodiment, different from the case of the above-described first embodiment, a further effect can be obtained by dividing the light source into N regions. The reason will be described in detail below.

As in the case of the first embodiment, there are 100 pixels for which red display is to be performed, and R100 = 100
(Arbitrary unit). Then, it is assumed that one of the 100 red display pixels wants to perform red display at a luminance of 80 (arbitrary unit), and the other pixels perform red display of 50 or less. Here, when the driving as in the first embodiment is performed, it becomes necessary to illuminate the red light emitting diode at MAXR = 80. However,
When the light source region is divided into a plurality as in this embodiment,
MAXR = 80 is set only for the red light emitting diode in the region including the pixel (arbitrary unit) of 80 (arbitrary unit), and MAXR = 50 is set for the red light emitting diode in the other region. Power consumption can be further reduced.

Although the present invention has been described with reference to specific examples, a similar effect can be obtained by using a white EL element, a white organic electroluminescent element or the like in addition to a light emitting diode as a backlight.

Specifically, a color display liquid crystal panel of about 5 inches (twisted nematic mode, display capacity QVGA, with color filter) is manufactured by a known method, and a white EL is provided by Nidec Home Electronics Corporation.
When a backlight is obtained and this is used as a backlight to form a liquid crystal display device similar to that in Embodiment 1, in the case of displaying an image such as a landscape, compared with a case where the present invention is not used,
About half.

A color display liquid crystal panel of about 5 inches (twisted nematic mode, display capacity QVG)
A, with a color filter) was manufactured by a known method, and a white organic electroluminescent device was obtained from Matsushita Giken Co., Ltd., and when used as a backlight, excellent characteristics in power consumption characteristics were exhibited.

[0032]

The present invention contributes to a reduction in the power consumption of the backlight, which accounts for the majority of the power consumption of the transmissive liquid crystal display device, and is of great industrial value.

[Brief description of the drawings]

FIG. 1 is a configuration sectional view of a liquid crystal display device according to the present invention.

FIG. 2 is a perspective view of a liquid crystal display device according to the present invention.

FIG. 3 is a perspective view of a backlight according to the present invention.

FIG. 4 is a flowchart of an operation of an arithmetic circuit of the liquid crystal display device according to the present invention.

FIG. 5 is a sectional view of a configuration of a liquid crystal display device according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Emission side polarizing plate 2 Glass substrate 3 Color filter 4 Transparent electrode 5 Liquid crystal layer 6 Transparent electrode 7 Thin film transistor (TFT) attached to each pixel 8 Glass substrate 9 Incident side polarizing plate 10 Backlight including light source and light guide plate 11 Reflection Board 12 Liquid crystal panel 13 Backlight including light source and light guide plate 14 Reflector 15 Memory and arithmetic circuit for information to be displayed 16 Connection to liquid crystal panel 17 Brightness switching circuit for backlight 18 Information memory and arithmetic circuit 15 to backlight 19 Connection to the backlight switching circuit 17 from the backlight 19 Connection from the backlight switching circuit 17 to the backlight 20 A large number of light-emitting diodes 21 arranged in the order of red, green, and blue 21 A light guide plate formed of acrylic 22 Back surface of the light guide plate Many projections formed on 23 Liquid crystal cell 24 Acrylic light guide 25 projection 26 groups of LEDs

Claims (3)

[Claims] 1. A liquid crystal display device using light emitting diodes corresponding to three primary colors as a backlight, and comparing and calculating luminance information of each pixel in one frame to calculate a maximum luminance of each of the three primary colors in one frame. A liquid crystal display device comprising: determining a luminance of a pixel having the light-emitting diode; and setting an emission luminance of the light-emitting diode when displaying the one frame to the maximum luminance. 2. A liquid crystal display device which divides one frame into a plurality of regions and uses light emitting diodes corresponding to three primary colors as a backlight corresponding to the plurality of regions, wherein each pixel in the region is The luminance information is compared to calculate the luminance of a pixel having the maximum luminance of each of the three primary colors in the area, and the light emission luminance of the light emitting diode when displaying the area is set to the maximum luminance. Liquid crystal display device. 3. The liquid crystal display device according to claim 1, wherein an electroluminescent element or an organic electroluminescent element is used as the backlight instead of the light emitting diode.