JP2003044016A - Liquid crystal display device and driving method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve such a problem that LEDs have to be used in a poor luminous efficiency area thereof and a power utilization factor decreases when trying to increase brightness for pulse-driving. SOLUTION: Among three light sources, a better luminous efficiency light source is decreased of its emitting period, the remaining time is allocated to the emitting period of the poor luminous efficiency light sources, correcting the brightness at the light emitting time.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a display control technique for a display device, and more particularly to a technique suitable for driving a liquid crystal display device.

[0002]

2. Description of the Related Art A color-sequential display system (field-sequential display) in which red, green, or blue images are displayed, and in conjunction with that, illumination according to the respective colors is radiated in any order from the entire surface or the back surface to perform color display. In the liquid crystal display device of the color type), the lighting period of the light source (hereinafter, backlight) is the same regardless of the luminous efficiency of the light source.
This state is shown in FIG. Here, 401 is the light emission timing of the red light source, 402 is the light emission timing of the green light source, 4
Reference numeral 03 is a light emission timing of a blue light source, TR, TG, and TB are light emission periods of red, green, and blue, respectively, and TR = TG = T.
B.

[0003]

In recent years, the number of cases in which a liquid crystal display device is used in a portable device is rapidly increasing, and accordingly, it is required to reduce the power consumption of the liquid crystal display device. In the color sequential display system, since the backlight is colored, the color filter which has been conventionally required is not necessary.
Therefore, since the light transmittance of the liquid crystal display element can be made higher than that of the conventional one, the power consumption can be theoretically reduced as compared with the case of displaying the same brightness.

However, since the three primary colors of light must be displayed within one frame period, the backlight must be turned on / off, that is, blinked.

When the backlight blinks,
In order to obtain the same brightness as in the case of constantly lighting, it is necessary to increase the brightness during lighting (hereinafter referred to as peak brightness). Here, the ratio of the lighting period in the arbitrary period T will be referred to as a "lighting rate". For example, in FIG.
As shown in (a), it is assumed that the luminance at a lighting rate of 100% of a certain light source is L in an arbitrary period T. On the other hand, as shown in FIG. 9B, when the lighting rate is 10% (that is, when the lighting period is T × 0.1), if the luminance of 10 times L is not applied during lighting, the period T The effective luminance (hereinafter, referred to as the effective luminance) does not match L.

As the luminous efficiency η, η = (luminance / electric power), that is, the ratio of the applied electric power to the luminance is considered. As shown in FIG. 10A, if the characteristics of the applied power and the obtained brightness are linear, the luminous efficiency is constant regardless of the applied power as shown in FIG. Is 100% or 10%, the power required to obtain the same effective luminance is the same. In FIG. 10, 801 is an arbitrary power, 802 is 10 times the power of 801, and 803 is the brightness obtained when the power 801 is input.
Reference numeral 804 denotes the luminance obtained when the power 802 is turned on, and the luminance 804 = (luminance 803) × 10.

However, as shown by the solid line in FIG. 11 (a), when the characteristics of the applied power and the obtained brightness are not linear, especially when the increase in the brightness is smaller than the increase in the applied power. As shown in FIG. 11B, the higher the input power, the worse the light emission efficiency. Here, 901 is an arbitrary power, 902 is 10 times the power of 901, and 903 is 90.
The electric power larger than 2, the electric power 904 is the brightness obtained when the electric power 901 is input, and the electric power 905 is 10 times the brightness of 904.
6 is the brightness obtained when power 902 is input,
905> 906. When a light source having such characteristics is used to obtain the same effective luminance as in the previous example with a lighting rate of 10% and a lighting rate of 100%, a power of 903, which is more than 10 times the power of 902, is generated. It will have to be thrown in. That is, it is used in a region where the light emission efficiency is low, and the power use efficiency is low.

[0008]

In order to solve this problem, in the first invention of the present application, a light source capable of turning on / off the first, second and third color lights which are the three primary colors of light, and the above-mentioned light source. In a display device provided with a liquid crystal display element for switching light received from, the first light source and the other light sources have different light emission periods.

Further, in the second invention of the present application, a light source capable of turning on / off the first, second and third color lights of the three primary colors of light, and a liquid crystal display element for switching light received from the light source are provided. In the display device, the first light source and the second light source.
The light emitting periods of the light source of No. 3 and the third light source are made different from each other.

Further, in the third invention of the present application, the first, second and third color lights which are the three primary colors of light are lit so that the white balance of the display device is not lost even if the light emitting period is changed.
In a display device including a light source that can be turned off and a liquid crystal display element that switches light received from the light source, the effective luminance is adjusted by the light emission period of the light source and the luminance at the time of light emission.

Further, in the fourth invention of the present application, light sources for the first, second and third color lights which are the three primary colors of light, and a plurality of dimming devices for adjusting the brightness of the plurality of light sources by the amplitude of the terminal voltage. Department,
A plurality of control units for controlling the light emission periods of the plurality of light sources are provided, and the plurality of control units are controlled so that the light emission periods of the first light source and other light sources are different, and at the same time, white balance is controlled by the plurality of light sources. The liquid crystal display device is realized by adjusting the light control section.

Further, in the fifth invention of the present application, the light sources of the first, second and third color lights which are the three primary colors of light and a plurality of dimming devices for adjusting the brightness of the plurality of light sources by the amplitude of the terminal voltage. Department,
A plurality of control units for controlling the light emission periods of the plurality of light sources, and the plurality of control units control so that the light emission periods of the first light source, the second light source, and the third light source are all different;
At the same time, the liquid crystal display device is realized by adjusting the white balance by the plurality of light control units.

Further, in the sixth invention of the present application, light sources for the first, second and third color lights which are the three primary colors of light, and a plurality of dimming devices for adjusting the brightness of the plurality of light sources by the amplitude of the terminal voltage. Department,
A plurality of control units for controlling the light emission period of the plurality of light sources are provided, and by adjusting the light emission period and the brightness at the time of light emission of the plurality of light sources by the plurality of control units and the plurality of light control units, any The present invention realizes a liquid crystal display device capable of adjusting effective luminance during a period.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to FIGS. 1 to 7. Here, a case where a light emitting diode (LED) is used as a light source will be described as an example.

(Embodiments of the first to third inventions of the present application)
The power-brightness characteristics of LEDs depend on the materials used. For example, the GaAsAl-based material used for red is
Since the characteristics are close to those in FIG. 10, the brightness obtained with respect to the input power is almost the same in both direct-current driving (DC driving) in which the lighting rate is 100% and pulse driving in which lighting and extinction are repeated. According to an experiment conducted by the inventor, the luminance at a lighting rate of 10% is about 80% at a lighting rate of 100% when the effective power supplied to the LED is about 30 mW.
That was all. Hereinafter, a light source having a characteristic close to that of FIG. 10 will be referred to as a “red light source”.

However, for example, green and blue LEDs are shown in FIG.
Generally, the characteristics shown in FIG.
The luminance obtained differs between when driving and when pulse driving. That is, even if the electric power supplied during a certain period T (hereinafter referred to as the effective electric power) is the same, the luminance obtained in the pulse driving is lower than that in the DC driving. According to an experiment conducted by the inventor, when the effective power supplied to the LED is about 30 mW, the brightness at a lighting rate of 10% is about 30% for green and about 40% for blue. Met. That is, even if the same power is applied, at a lighting rate of 10%, only about 30 to 40% of the brightness at a lighting rate of 100% can be obtained. After that, the light source with the characteristics similar to FIG.
It will be referred to as a “green light source” or a “blue light source”.

Therefore, when a green light source or a blue light source having the characteristics shown in FIG. 11 is used, when the same electric power is supplied during an arbitrary period T, the larger the lighting rate, the better the luminous efficiency. This means that it can be used in the area, and high brightness can be obtained.

Therefore, in the present invention, of the three light sources, the light emitting period of the red light source closest to the characteristic shown in FIG. 10 is shortened, and the remaining time is allocated to the lighting period of the green light source or the blue light source. By making the green light source or the blue light source usable in a region having a higher light emission efficiency, the power utilization efficiency of the green light source or the blue light source is improved.

FIG. 1 shows the light emission timing of each light source using the first invention of the present application. In FIG. 1, 101 is the light emission timing of the red light source, and the light emission period is TR1. Further, 102 is the light emission timing of the green light source, and the light emission period is TG1. Further, 103 is the light emission timing of the blue light source, and the light emission period is TB1. In this example, TR
1 is shorter than TR, and the remaining time is TG1,
By evenly allocating the light sources to TB1, it is possible to extend the light emission period of the green light source and the blue light source and to use the light sources in a power region with good light emission efficiency.

As mentioned above, the light emitting period of the red light source is shortened and the light emitting periods of the green and blue light sources are lengthened.
Since the light emission period and the luminance are in a relative relationship, the luminance of red decreases and the luminances of green and blue increase on the contrary, so that the white balance is lost and the image quality remarkably deteriorates. In order to avoid this, for a red light source with a short lighting period, the peak brightness may be increased by the proportion of the reduced light emitting period. Further, regarding the green or blue light source in which the lighting period is increased, the peak luminance may be reduced by the proportion of the increased light emitting period. These processes will be called “luminance correction”.

A method of brightness correction will be described with reference to FIG.

In FIG. 4, 501 to 503 represent the light emission timing and brightness of each light source in the conventional method. 5
01 corresponds to a red light source, 502 corresponds to a green light source, and 503 corresponds to a blue light source. TR, TG, and TB represent the light emitting period of each light source, and LR, LG, and LB represent the peak luminance of each light source. Here, TR = TG = TB and LR = LG
= LB.

Next, reference numerals 504 to 506 represent the light emission timing and the brightness of each light source when the driving according to the present invention is performed. Reference numeral 504 corresponds to a red light source, 505 corresponds to a green light source, and 506 corresponds to a blue light source. TR5, TG5, and TB5 represent the light emitting period of each light source, and LR5, LG5, and LB5 represent the peak luminance of each light source.

First, focusing on the red light source, the light emission period is T
Since it changes from R to TR5, the effective brightness is also (TR5 /
TR) doubled. Therefore, LR5 is replaced by LR × (TR
/ TR5). As a result, the areas of 501 and 504 become equal, the effective luminance becomes equal, and luminance correction becomes possible. Similarly, for the green light source and the blue light source, LG
5 is LG × (TG / TG5), LB5 is LB × (TB /
TB5). As a result, the effective luminance of each light source remains the same even if the light emitting period changes, and the image quality is maintained. When the light emission period is changed using all the inventions described in the present application, the peak brightness may be corrected based on the above concept.

By the way, the human eyes have different sensitivities depending on the wavelength of light, and the sensitivity is green, red, and blue in order of increasing sensitivity. Roughly speaking, the human eye perceives white when the power ratio of red: green: blue light is approximately 3: 6: 1. As described above, since the sensitivity to green is the highest, the white balance of the display device is also adjusted with the power of green being the maximum. Therefore, green power is most needed in normal video equipment, and blue power is not so much needed.

Therefore, as shown in FIG. 2, the ratio of the light emitting period of the red light source to the light emitting period of the blue light source is reduced within one frame, and the remaining period is allocated to the green light emitting period. Here, 201 is the emission timing of the red light source, 2
Reference numeral 02 is a light emission timing of the green light source, and 203 is a light emission timing of the blue light source. The light emission periods of the red, green, and blue light sources are TR2, TG2, and TB2, respectively. Here, TR2 is shorter than TR, and TB2 is a shorter period than TB. TG2 is a longer period than TG. By doing so, the green light emission period that requires the highest power can be lengthened, so that it can be used in a region where the light emission efficiency is higher. As a result, the power utilization efficiency of the display device as a whole is improved, and it is possible to further reduce the power consumption when used in a mobile device.

Alternatively, according to the second invention of the present application, as shown in FIG. 3, all the periods obtained by reducing the emission period of the red light source are allocated to the green emission period, and the blue emission period is left as it is. You may stay. Here, 301 is the light emission timing of the red light source, 302 is the light emission timing of the green light source, and 303 is the light emission timing of the blue light source. Also,
The emission periods of the red, green, and blue light sources are TR3 and TG, respectively.
3 and TB3. Also, TR3 is shorter than TR, TG3 is longer than TG, and TB3 = TB.
Is. By doing so, the green light emission period requiring the highest power can be lengthened, the green light can be used in a region having high light emission efficiency, and the light power can be increased. Further, since the blue light source does not shorten the light emission period, it is not used in a region where the light emission efficiency is poor, and the power utilization efficiency does not decrease. This allows
The power use efficiency of the display device as a whole is improved, and it is possible to further reduce power consumption when used in a mobile device.

As described above, the power utilization efficiency can be improved by optimizing the light emission period of each light source in accordance with the power-light emission efficiency characteristic of the light source and the required light power.

Up to now, within one frame period, red,
I explained the case where green and blue each emit light once.
The same effect is obtained even when each light source emits light many times.

In the color-sequential display type display device, when a moving image is displayed and followed by the eyes of an observer, the temporal difference in the light emission timing of each display color appears as a spatial difference. The phenomenon of "color breakup" occurs.

For example, in the case where a white square pattern moves left and right in a black background, the left and right ends of the square appear to be colored red or blue. As described above, the color breakage is caused by the temporal difference in the light emission timing of each color. Therefore, if the temporal difference is reduced, the color breakup can be reduced.

Therefore, if a light source that shortens the light emission period, for example, a red light source is set as the light source that first emits light in one frame, it is possible to reduce red color breakage, and the power utilization efficiency of the display device. At the same time, the effect of improving

When the light emitting period of the light source is shortened as shown in FIG. 2 and the surplus time is assigned to the light emitting period of the remaining one light source, two light sources for shortening the light emitting period, for example, red light and blue light, are used. By setting the light emission order to the beginning or the end of one frame, it is possible to reduce the color breakup of both red and blue, and at the same time, the effect of improving the power use efficiency of the display device can be obtained.

(Embodiments of the fourth to sixth inventions of the present application)
FIG. 5 shows an example of a circuit used for the light source of the liquid crystal display device according to the fourth to sixth inventions of the present application. 601 is a power supply terminal, 60
2 is a buffer circuit, 603 is a bypass capacitor, 60
4 is a red light source, 605 is a green light source, 606 is a blue light source,
607 is a switching element, 608 is 604, 605,
A control signal generation circuit for controlling the light emission timing of 606,
Reference numeral 609 is a video signal input terminal, and 610 is a variable resistor.

The variable resistor 610 is an adjusting unit for performing brightness correction when the light emitting period of the light source is changed, and for adjusting individual variations in voltage-luminance characteristics of the LED and white balance. By making red, green, and blue independent, independent reference voltages can be obtained. The reference voltage generated by the 610 is red,
It is input to the green and blue buffer circuits 602. The buffer circuit 602 amplifies the input reference voltage and outputs L
Power is supplied to the anode terminal of the ED. By connecting the bypass capacitor 603 to the output section of the buffer circuit,
The bias current of the buffer circuit can be minimized, and the power constantly consumed in the buffer circuit can be reduced. In addition, it is possible to prevent the rising of the voltage supplied to the LED from becoming blunt.

A switching element 607 is connected to the cathode terminal of the LED. The switching element 607 opens and closes the circuit according to the control signal from 608, and the LED emits light when the circuit is closed. 608 sends a control signal corresponding to the light emitting period of each light source as shown in FIGS. 1 to 3 to 607 according to the video signal input from 609.
Here, the light emission timings of red, green, and blue are stored in advance in 608, and a control signal is generated based on the stored information.

Next, FIG. 6 shows the entire structure. In FIG. 6, 701 is an input terminal of a video signal, 702 is a controller for controlling a source driver and a gate driver, and backlight (backlight), 703 is a source driver, 704 is a backlight, 705 is a gate driver,
Reference numeral 706 is a liquid crystal display panel.

The controller 702 has a frame memory capable of storing a video signal for one screen in order to process the video signal input from the outside into a state suitable for the color sequential display system. The video signal is temporarily stored in the frame memory. Then, it is divided into red, green, and blue video signals and transmitted in order to the source driver with the color order fixed. At the same time, control signals such as a clock signal, a latch pulse, and a start pulse are sent to the source driver. It also sends a control signal required for scanning to the gate driver. This state is shown in FIG. In FIG. 7, 1101 is a control signal of a red backlight, and 110
2 is a control signal for a green backlight, 1103 is a control signal for a blue backlight, 1104 is a backlight for a period for writing a voltage to the liquid crystal, and a period for the liquid crystal to respond to the written voltage, respectively. It is a period during which the light is turned on and an image is displayed. Here, as an example, the operation when writing a red video signal will be described. First, in the writing period 1104, a red video signal is written in the liquid crystal panel.
After that, after a period 1105 until the liquid crystal responds to the written voltage, the red backlight is emitted at the timing of the backlight irradiation period 1106. Similarly,
It also processes green and blue video signals. In this way, color display is performed by sequentially displaying each color. Regarding the period for illuminating the backlight, the light emission period of the light source may be optimized according to the power-light emission efficiency characteristic of the light source and the required brightness.

Since the control of the source driver and the gate driver is the same as that of the conventional liquid crystal display device, the description thereof is omitted here.

Although the use of the LED as the light source has been described above as an example, the present invention is not limited to this, and can be applied to the one using an organic EL element or a fluorescent lamp.

[0041]

As described above, according to the first aspect of the present invention, the first, second and third color lights which are the three primary colors of light are lit.
In a display device including a light source that can be turned off and a liquid crystal display element that switches light received from the light source, by making the light emission periods of the first light source and other light sources different, the power utilization efficiency of the backlight Can be increased.

Further, according to the second aspect of the present invention, it is provided with a light source capable of turning on / off the first, second and third color lights which are the three primary colors of light, and a liquid crystal display element for switching the light received from the light source. In the display device, the first light source and the second light source are provided.
By making the light emitting periods of the light source of No. 3 and the third light source different from each other, it is possible to improve the power use efficiency of the backlight.

Further, according to the third aspect of the present invention, it is provided with a light source capable of turning on / off the first, second and third color lights which are the three primary colors of light, and a liquid crystal display element for switching light received from the light source. In the display device, with the light emission period of the light source and the luminance at the time of light emission, it is possible to adjust the effective luminance in an arbitrary period, and the white balance is not lost even if the light emission period of the backlight is changed, Display quality can be maintained.

According to the fourth aspect of the present invention, the light sources of the first, second and third color lights which are the three primary colors of light and a plurality of adjustments for adjusting the brightness of the plurality of light sources by the amplitude of the terminal voltage are provided. Light part,
A plurality of control units for controlling the light emission periods of the plurality of light sources are provided, and the plurality of control units are controlled so that the light emission periods of the first light source and other light sources are different, and at the same time, white balance is controlled by the plurality of light sources. By adjusting with the light control unit, the power utilization efficiency of the backlight can be improved, and a display device with low power consumption can be obtained.

According to the fifth aspect of the present invention, the light sources for the first, second and third color lights which are the three primary colors of light and a plurality of adjustments for adjusting the brightness of the plurality of light sources by the amplitude of the terminal voltage are provided. Light part,
A plurality of control units for controlling the light emission periods of the plurality of light sources, and the plurality of control units control so that the light emission periods of the first light source, the second light source, and the third light source are all different;
At the same time, the white balance is adjusted by the plurality of light control units, so that the power utilization efficiency of the backlight can be improved and a display device with low power consumption can be obtained.

According to the sixth aspect of the present invention, the light sources for the first, second and third color lights which are the three primary colors of light and a plurality of adjustments for adjusting the brightness of the plurality of light sources by the amplitude of the terminal voltage are provided. Light part,
A plurality of control units for controlling the light emission period of the plurality of light sources are provided, and by adjusting the light emission period and the brightness at the time of light emission of the plurality of light sources by the plurality of control units and the plurality of light control units, any It is possible to adjust the effective luminance during the period, and it is possible to obtain a display device in which the white balance is not lost even if the light emission period of the backlight is changed and the display quality is not impaired.

When the first to sixth inventions of the present application are used, the efficiency of use of the electric power of the light source is improved, so that the power consumption can be reduced and the environment of the earth and the space environment can be reduced.

[Brief description of drawings]

FIG. 1 is a diagram showing a light emission timing of a light source of each color according to the first invention of the present application.

FIG. 2 is a diagram showing a light emission timing of a light source of each color according to the first invention of the present application.

FIG. 3 is a diagram showing a light emission timing of a light source of each color according to the second invention of the present application.

FIG. 4 is a diagram showing light emission timings of light sources of respective colors according to the third invention of the present application.

FIG. 5 is a diagram showing a circuit of a light source unit of a liquid crystal display device according to a fourth invention, a fifth invention, or a sixth invention of the present application.

FIG. 6 is a diagram showing a liquid crystal display device according to a fourth invention, a fifth invention, or a sixth invention.

FIG. 7 is a diagram showing a control timing of a liquid crystal display element and a backlight.

FIG. 8 is a diagram showing light emission timings of light sources of respective colors by a conventional method.

FIG. 9 is a diagram showing a relationship between a light emission period, light emission luminance, and effective luminance.

FIG. 10 is a diagram showing characteristics of a light source whose luminous efficiency does not depend on electric power.

FIG. 11 is a diagram showing characteristics of a light source whose luminous efficiency depends on electric power.

[Explanation of symbols]

101 Light emission timing of the red light source 102 Green light source timing 103 Blue light source emission timing TR Light emission period of the red light source in the conventional method TG Light emitting period of the green light source in the conventional method TB Emission period of blue light source in conventional method

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Claims (8)

[Claims] 1. A display device comprising a light source capable of lighting and extinguishing first, second and third color lights of three primary colors of light, and a liquid crystal display element for switching light received from said light source, said first device comprising: The method for driving a liquid crystal display device, wherein the light emitting period of the light source of 1 is different from that of the other light source. 2. A display device comprising a light source capable of lighting and extinguishing first, second and third color lights of three primary colors of light, and a liquid crystal display element for switching light received from said light source, wherein said first The method for driving a liquid crystal display device, wherein the light emitting periods of the second light source and the third light source are all different. 3. The light source other than the first or last light source emits light for a longer period of time than the lighting period of the first or last light source for one frame period. 7. A method for driving a liquid crystal display device according to. 4. A display device comprising a light source capable of lighting and extinguishing first, second and third color lights which are the three primary colors of light, and a liquid crystal display element for switching light received from said light source. A method for driving a liquid crystal display device, characterized in that effective luminance in an arbitrary period is adjusted by a light emitting period and a luminance at the time of light emission. 5. A light source of first, second, and third color lights that are the three primary colors of light, a plurality of light control units that adjust the brightness of the plurality of light sources by the amplitude of a terminal voltage, and the plurality of light sources. Of the first light source and the other light sources are controlled by the plurality of control units so that the light emission periods of the first light source and the other light sources are different from each other, and at the same time, white balance is adjusted to the plurality of light control units. A liquid crystal display device characterized by being adjusted. 6. A light source of first, second, and third color lights which are the three primary colors of light, a plurality of light control units for adjusting the brightness of the plurality of light sources by the amplitude of a terminal voltage, and the plurality of light sources. A plurality of control units for controlling the light emission period of the first light source and the second light source.
2. The liquid crystal display device, wherein the plurality of control units control the light emission periods of the light source and the third light source so that they are all different, and at the same time, the white balance is adjusted by the plurality of light control units. 7. The light source other than the first or last light source emits light for a longer period of time than the lighting period of the first or last light source for one frame period. The liquid crystal display device according to item 1. 8. A light source of first, second, and third color lights that are the three primary colors of light, a plurality of light control units that adjust the brightness of the plurality of light sources by the amplitude of a terminal voltage, and the plurality of light sources. By controlling the light emitting period and the brightness at the time of light emission of the plurality of light sources by the plurality of control units and the plurality of light control units, the effective luminance in an arbitrary period is provided. A liquid crystal display device characterized by adjusting.