KR20140116716A - Liquid Crystal Display Device Including Compensating Circuit For Blue Light - Google Patents

Abstract

The present invention provides a liquid crystal display device including: a power supply unit for supplying a first power supply voltage; a red and green gamma voltage supply unit which generates a red and green data voltage by receiving the first power supply voltage from the power supply unit; a power supply voltage modulation unit which receives the first power supply voltage from the power supply unit, and generates a second power supply voltage by modulating the first power supply voltage depending on a temperature; a blue gamma voltage supply unit which generates a blue gamma voltage by receiving the second power supply voltage from the power supply voltage modulation unit; and a liquid crystal panel which displays an image by using the blue data voltage and the red and green data voltage.

Description

[0001] The present invention relates to a liquid crystal display device including a blue light compensation circuit,

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a liquid crystal display provided with a blue light compensation circuit for compensating for a blue color shift caused by an increase in temperature.

In general, a liquid crystal display device is composed of a liquid crystal panel filled with a liquid crystal and operated according to an electric signal, and a backlight module supplying light thereto. Conventional backlight module uses CCFL (Cold Cathode Fluorescent Lamp), but as the technology develops in recent years, the thickness of the liquid crystal display becomes thinner, and accordingly, it is thinner and smaller than CCFL, (Light Emitting Diode) device capable of displaying a light emitting diode (LED).

The light source color used in the backlight module is white so that the emitted light passes through the color pattern of the liquid crystal panel to enable accurate color representation. For this purpose, there are single-chip and multi-chip methods for producing white light using LED devices. In the single-chip method, a white color is displayed by inserting a fluorescent material into a blue or purple LED element. In the multi-chip method, two colors of a complementary color relationship, or a mixture of colors of three or more colors are used to represent white. It consumes less power than CCFL, has a long lifetime, and has the fastest response speed.

However, the backlight module using the LED element shows white light having a blue color rather than a normal white light according to the color change due to heat emitted from the LED element and physical properties of the liquid crystal, which will be described in detail with reference to FIG.

FIG. 1 shows a color coordinate shift of a white light according to a heat increase emitted from a conventional backlight module.

As shown in FIG. 1, light emitted from a conventional backlight module using an LED element gradually becomes blue as heat is increased. Here, the initial value (10) of the color coordinate of the light of the backlight module represents a value at 31.8 DEG C, and represents the color in which the x, y axes based on the CIE 1931 XYZ color space are located at 0.3036 and 0.3168, respectively. In this color coordinate initial value 10, the values of x and y are gradually decreased as the temperature increases. Looking at the measured color coordinates 20 of the light displayed by the backlight module after being heated to 45 ° C by the LED device, It can be seen that the x, y axes of the 1931 XYZ color space reference represent 0.2990 and 0.3077, respectively. In the CIE 1931 XYZ color space, a strong blue color appears as the x and y coordinates become smaller. In the case of the measured value (20), x shifts to 0.0046 and y shifts to 0.0091 at the initial value (10) It is possible to observe white light having a higher ratio.

In addition, when the heat of the backlight module is transmitted to the liquid crystal panel and the liquid crystal layer is heated, the effective phase delay value of the liquid crystal layer is changed, so that the image is shifted further toward the blue side, which will be described in detail with reference to FIG.

2 is a view showing an effective phase delay value by temperature of a conventional liquid crystal display device heated by a backlight module.

The graph shown in FIG. 2 particularly relates to a lateral horizontal mixed electric field type liquid crystal display device. 2, the phase delay initial value 30 is about 338 nm in a state where the temperature of the liquid crystal panel is 20 ° C, but the phase delay value decreases as the temperature gradually increases, About 318 nm, and from the second measured value 40 to about 303 nm. This phase delay reduction causes blue light to pass through the liquid crystal layer. Accordingly, there arises a problem that the user can not achieve the exact color and performance desired by the backlight module that emits blue light and white light mixed with blue light.

An object of the present invention is to provide a blue light compensation circuit capable of minimizing a change in color coordinates of white light generated according to an LED element of a backlight unit and a blue color of a liquid crystal panel according to an increase in temperature, and a liquid crystal display device including the same.

In order to achieve the above object, the present invention provides a power supply apparatus comprising: a power supply unit for supplying a first power supply voltage; A red / green gamma voltage supplier for receiving the first power source voltage from the power source and generating an red / green data voltage; A power supply voltage modulator receiving the first power supply voltage from the power supply unit and modulating the first power supply voltage according to the temperature to generate a second power supply voltage; A blue gamma voltage supplier for receiving a second power supply voltage from the power supply voltage modulator to generate a blue data voltage; And a liquid crystal panel for displaying an image using the red / green data voltage and the blue data voltage.

The power supply voltage modulating unit includes a thermistor and a resistor connected between the power supply unit and the thermistor, and a connection node between the resistor and the thermistor is connected to the blue gamma voltage supply unit.

The power supply voltage modulator includes a thermistor and a control element connected to the thermistor. The control element modulates the first power supply voltage to the second power supply voltage according to a signal received from the thermistor, Gamma voltage supply unit.

The power supply voltage modulator further includes an analog-to-digital converter connected between the control element and the thermistor.

According to another aspect of the present invention, there is provided an image processing apparatus comprising: a timing controller for supplying red / green image data and blue image data; A data driver for receiving the red / green image data from the timing controller; A data modulator receiving the blue image data from the timing controller and modulating the blue image data according to the temperature to generate modulated blue image data; A data driver for outputting red / green data voltages and blue data voltages using the red / green image data and the modulated blue image data; And a liquid crystal panel for displaying an image using the red / green data voltage and the blue data voltage.

The data modulator includes a thermistor, a selector coupled to the thermistor, and a memory coupled to the selector.

The data modulator further includes an analog-to-digital converter connected between the thermistor and the selection unit.

The selector compares the data received from the thermistor with the data stored in the memory, modulates the blue image data to generate the modulated blue image data, and transmits the modulated blue image data to the data driver.

The liquid crystal display device including the blue light compensation circuit according to the present invention adjusts the gamma of the blue pixel represented by the liquid crystal panel to the LED device of the backlight unit and the blue color of the liquid crystal panel, And modulates only the blue gamma so as not to affect the red / green gamma, thereby minimizing the luminance degradation of the liquid crystal display due to the compensation.

FIG. 1 shows a color coordinate shift of a white light according to a heat increase emitted from a conventional backlight module.
2 is a view showing an effective phase delay value by temperature of a conventional liquid crystal display device heated by a backlight module.
3 is a view schematically showing a configuration of a liquid crystal display device according to the present invention.
4 is a diagram illustrating a blue light compensation circuit according to the first embodiment of the present invention.
5 is a diagram illustrating a blue light compensation circuit according to a second embodiment of the present invention.
6 is a diagram illustrating a blue light compensation circuit according to a third embodiment of the present invention.
FIG. 7 is a graph illustrating a color coordinate change according to temperature of a liquid crystal display device including the compensation circuit according to the first to third embodiments of the present invention.
8 is a graph comparing luminance differences when a compensation method according to the present invention and a conventional compensation method are applied to a liquid crystal display device.

Specific details for carrying out the present invention will be described in detail below with reference to the drawings.

3 is a view schematically showing a configuration of a liquid crystal display device according to the present invention.

3, the liquid crystal display according to the present invention includes a power supply unit 101, a red / green gamma voltage supply unit 110, a blue gamma voltage supply unit 111, a timing control unit 150, a data driver 155 ), A gate driver 154, and a liquid crystal panel 165. Here, the liquid crystal display according to the present invention can reduce the luminance of blue light by lowering the blue gamma expressed by the liquid crystal panel 165 to prevent blue transition caused by the characteristics of the liquid crystal layer and the LED backlight. A power supply voltage modulating unit 191 may be added between the power supply unit 101 and the blue gamma voltage supply unit 111 to modulate the first power voltage VDD1 transmitted to the liquid crystal panel 165, The data modulator 192 may be added between the control unit 150 and the data driver 155 to change the value of the data voltage output from the data driver 155 to adjust the maximum value of the blue light represented by the liquid crystal display . In the liquid crystal display device thus constructed, a conventional red / green / blue voltage supply unit (not shown) including a resist ring for expressing gradation is divided into an red / green gamma voltage supply unit 110 and a blue gamma voltage supply unit 111 This structure will be described in detail below with reference to an embodiment.

4 is a diagram illustrating a blue light compensation circuit according to the first embodiment of the present invention.

4, the compensation circuit according to the first embodiment of the present invention is located in the power supply voltage modulating unit 191 of the liquid crystal display device and is provided between the power supply unit 101 and the blue gamma voltage supply unit 111 A first resistor 115 and a thermistor 120 are provided. At this time, the structure of the first resistor 115, the thermistor 120, and the line branched therebetween is in accordance with the distribution resistance law, so that the blue gamma voltage supply unit 111 is applied to the red / The second power supply voltage VDD2 is lower than the first power supply voltage VDD1. Here, the power supply voltages can be obtained from a plurality of register rings formed in each gamma voltage supply unit to comply with the distribution resistance law, and each node formed therein. In the first embodiment of the present invention, an NTC (Negative Temperature Coefficient) thermistor 120 whose resistance varies with temperature is taken as an example, and a temperature range of the thermistor 120 to be applied to the NTC will be described below.

The NTC thermistor 120 has a relatively high resistance value at a relatively low temperature for any one of the temperatures. For example, when the first power supply voltage VDD1 supplied by the power supply unit 101 is 5 V, The second power supply voltage VDD2 transmitted to the blue gamma voltage supply unit 111 is equal to the voltage value of the power supply 101 * (The resistance value of the thermistor 120 / the resistance value of the first resistor 115 + the resistance value of the thermistor 120)] becomes 4.98504V. Since the difference from the voltage 5V supplied by the power supply unit 101 is insignificant, the blue gamma voltage supply unit 111 can express the red / green gamma voltage supply unit 110 to exhibit a value very close to the luminance realized through each pixel have. Further, when heated to a relatively high temperature by the backlight module, the thermistor 120 has a relatively low resistance value. For example, when the first power supply voltage VDD1 supplied by the power supply unit 101 is 5V, the first resistor 115 is 10Ω, and the thermistor 120 exhibits a resistance value represented by 100Ω according to the temperature, The second power supply voltage VDD2 transmitted to the gamma voltage supply unit 111 is a sum of the voltage value of the power supply 101 and the resistance value of the thermistor 120 / resistance of the first resistor 115 and resistance of the thermistor 120, ] According to the formula of 4.54545V. The blue gamma voltage supply unit 111 supplies the luminance signal to the red / green gamma voltage supply unit 110 through the first and second power supply units 101 and 102, Can be expressed to exhibit a lower luminance compared to the case of FIG.

Accordingly, the second power supply voltage VDD2, which is transmitted to the blue gamma voltage supply unit 111 when the thermistor 120 is driven at a relatively low temperature, is connected to the power supply unit 101 And a second power supply voltage VDD2 that is transmitted to the blue gamma voltage supply unit 111 at the time of driving at a relatively high temperature is supplied to the power supply unit 101. The second power supply voltage VDD2 has a high resistance value so as to be a voltage similar to the first power supply voltage VDD1, An element having a low resistance value is used so as to be a voltage lower than the first power supply voltage VDD1.

The red / green gamma voltage supplier 110 applies the first power source voltage VDD1 uniformly to the first and second power source voltages VDD1 and VDD2 without any change in temperature. The blue gamma voltage supply unit 111 that adjusts the gray level of the blue pixel while the second power source voltage VDD2 repeats the increase and decrease is compensated for the blue transition of the liquid crystal display device according to the temperature change.

5 is a diagram illustrating a blue light compensation circuit according to a second embodiment of the present invention.

5, the compensation circuit according to the first embodiment of the present invention is disposed in the power supply voltage modulating unit 191 of the liquid crystal display device and is provided between the power supply unit 201 and the blue gamma voltage supply unit 211 The control element 230, the analog-to-digital converter 231, and the thermistor 220 are connected to each other. The red / green gamma voltage supply unit 210 and the blue gamma voltage supply unit 211 are separated from each other. The red / green gamma voltage supply unit 210 and the red / Connected to a control element 230 for outputting a second power supply voltage VDD2 after branching at one point of the wiring for connecting the thermistor 220 to the control element 230. The control element 230 is connected to the analog- 231 and a blue gamma voltage supply unit 211 are connected. Here, the thermistor 220 is an example of the NTC type thermistor mentioned in the first embodiment, and one element may be used to measure the temperature inside the liquid crystal display device. In addition, the analog-to-digital converter 231 may omit a case where the controller 230 having a function of performing a predetermined command or a circuit performing such a function has an analog-to-digital conversion function.

The control element 230 converts an analog signal generated in the thermistor 220 into a digital signal through an analog-to-digital converter 231 and receives the input signal. The control element 230 receives the temperature signal and a second power supply voltage (V DD2) to the blue gamma voltage supply unit 211. This is a structure in which the compensation circuit according to the first embodiment of the present invention can prevent an error that may occur due to the instability of the thermistor (120 in FIG. 3).

In this case, the controller 230 receiving the resistance value of the thermistor 220 that repeats the increase / decrease according to the temperature changes the second power supply voltage Vs applied to the blue gamma voltage supplier 211 When the temperature of the liquid crystal display device becomes high, the second power source voltage VDD2 decreases and the resistance value increases when the liquid crystal display device becomes relatively low. 2 power supply voltage (VDD2) is increased so that the gray level of the blue pixel is adjusted according to each temperature, so that compensation for the blue variation is performed.

6 is a diagram illustrating a blue light compensation circuit according to a third embodiment of the present invention.

6, the compensation circuit according to the third embodiment of the present invention is located in a data modulator (192 in FIG. 3), and is provided between the timing controller 360 and the data driver 355, 350, an analog-to-digital converter 331, a thermistor 320, and a selector 340. This is a conventional structure in which image data for each subpixel constituting a liquid crystal panel is divided into red / green pixels and blue pixels, and the timing controller 360 controls the red / green pixels The data RG is directly transmitted to the data driver 355 without modulation and the blue image data B which is a signal for the blue pixel is converted into the modulated blue image data B ' To the data driver 355. The selector 340 is connected to an analog-to-digital converter 331 and a thermistor 320 to measure the temperature of the surrounding environment. The selector 340 having the thermistor 320 may adjust the gray level of the blue image data B according to the temperature of the liquid crystal display so that the modulated blue image data B ' And a memory unit 350 in which modulation blue image data B 'for each gradation according to temperature is recorded. Here, the thermistor 320 is an example of the NTC type thermistor mentioned in the first embodiment, and one element may be used to measure the temperature inside the liquid crystal display device.

The timing controller 360 transmits the red / green image data RG to the data driver 355 and transmits the blue image data B to the data driver 355. The selector 340 receives the blue image data B and inputs a signal from the thermistor 320 to compare the blue image data B with the modulation blue image data B ' Receive.

Here, since the signal value of the thermistor 320 is an analog type continuously appearing according to the temperature change, it is necessary to make a signal value of the digital type using the analog-to-digital converter 331. However, If there is a conversion function, the analog-to-digital converter 331 can be excluded.

The selector 340 receives the digital signal of the modulated thermistor 320 and compares the blue image data B with the data of the memory unit 350. As described above, the memory unit 350 includes a table for the modulation value of each gradation according to the temperature to adjust the brightness of each pixel of the screen. More specifically, the memory unit 350 includes the gradation of the blue light, Which is set so as to be in inverse proportion to the value of the table. In particular, the table represents a maximum of 256 gradations at room temperature (25 占 폚) and includes limiting the maximum 242 gradations of light at high temperatures (45 占 폚).

The selection unit 340 having the memory unit 350 having the table thus configured compares the temperature of the modulated thermistor 320 and the blue image signal B with a table for the modulation value by gradation according to the temperature The data driver 355 reads the modulated blue video signal B 'having the output voltage information corresponding to the modulated blue video signal B' from the memory unit 350 and transmits the modulated blue video signal B ' ') To limit the maximum luminance of the blue pixel represented by the panel. The liquid crystal display device driven in this manner can individually control the blue pixels, so that it is possible to compensate not only the blue transition occurring to the physical properties of the liquid crystal but also the light of the blue backlight module, It becomes possible to provide white light.

A comparison of the observed color coordinates with the conventional liquid crystal display device when the gamma is adjusted to reduce the blue light of the liquid crystal display device will be described in detail with reference to FIG.

FIG. 7 is a graph illustrating a color coordinate change according to temperature of a liquid crystal display device including the compensation circuit according to the first to third embodiments of the present invention.

As shown in FIG. 7, in the liquid crystal display device having the compensation circuit according to the first to third embodiments for adjusting the luminance of the blue pixel to compensate for the blue transition, the initial value 410 and the measured value 420 are similar In the conventional case, however, the white light rapidly moves to a short wavelength according to the temperature increase, and the white light transmitted through the liquid crystal display device becomes blue. 6 is a graph of CIE 1931 XYZ. The conventional measurement value 422 for the conventional backlight module is shifted to a position decreasing 0.007 in the Wx axis and 0.009 in the Wy axis at the initial temperature, However, the backlight module of the present invention has a slight difference of about 0.001 on the Wx axis and about 0.0001 on the Wy axis, thereby compensating for the blue variation so as not to be greatly different from the white light in the initial state.

As described above, when only the luminance of the blue pixel is reduced, not only the effect of compensating for the blue transition occurring in the liquid crystal display device and the backlight module but also the luminance reduction of the liquid crystal display device is improved. .

8 is a graph comparing luminance differences when a compensation method according to the present invention and a conventional compensation method are applied to a liquid crystal display device.

As shown in FIG. 8, in the present invention in which only the luminance of the blue LED element is compensated to compensate for the blue transition and the conventional invention in which the total voltage is reduced to compensate for the blue transition, a large difference appears in the overall luminance of the liquid crystal display do. The horizontal axis of FIG. 7 shows the gray level of light, and the vertical axis shows the luminance of the light in units of nit. When the luminance of the blue LED is adjusted by applying the compensation circuit according to the embodiment of the present invention, the total luminance of the liquid crystal display is finely reduced by about 3 to 4 nit in accordance with the gradation change, The luminance of the device varies greatly by about 62 to 64 nit depending on the gradation change, which is about 20 times higher than the luminance loss rate of the liquid crystal display according to the present invention.

As described above, the backlight module including the blue light compensation circuit for compensating for the blue transition of the liquid crystal display device by reducing the blue gamma of the liquid crystal panel and the liquid crystal display using the backlight module compensate for the increase in temperature, There is an effect that the luminance of the liquid crystal display device is not reduced.

Although the preferred embodiments of the present invention have been described above, the present invention is not limited thereto, and various modifications can be made without departing from the spirit of the present invention.

301: power supply unit 310: red / green LED element driver
311: blue gamma voltage supply unit 320: thermistor
331: Analog-to-digital converter 350:

Claims (8)

A power supply for supplying a first power supply voltage;
A red / green gamma voltage supplier for receiving the first power source voltage from the power source and generating an red / green data voltage;
A power supply voltage modulator receiving the first power supply voltage from the power supply unit and modulating the first power supply voltage according to the temperature to generate a second power supply voltage;
A blue gamma voltage supplier for receiving a second power supply voltage from the power supply voltage modulator to generate a blue data voltage;
A liquid crystal panel for displaying an image using the red / green data voltage and the blue data voltage,
And the liquid crystal display device.
The method according to claim 1,
Wherein the power supply voltage modulating unit includes a thermistor and a resistor connected between the power supply unit and the thermistor, and a connection node between the resistor and the thermistor is connected to the blue gamma voltage supply unit.
The method according to claim 1,
Wherein the power supply voltage modulator includes a thermistor and a control element coupled to the thermistor, wherein the control element modulates the first power supply voltage to the second power supply voltage according to a signal received from the thermistor, To the supply unit.
The method of claim 3,
Wherein the power supply voltage modulator further comprises an analog-to-digital converter connected between the control element and the thermistor.
A timing controller for supplying red / green image data and blue image data;
A data driver for receiving the red / green image data from the timing controller;
A data modulator receiving the blue image data from the timing controller and modulating the blue image data according to the temperature to generate modulated blue image data;
A data driver for outputting red / green data voltages and blue data voltages using the red / green image data and the modulated blue image data;
A liquid crystal panel for displaying an image using the red / green data voltage and the blue data voltage,
And the liquid crystal display device.
6. The method of claim 5,
Wherein the data modulator comprises a thermistor, a selector coupled to the thermistor, and a memory coupled to the selector.
The method according to claim 6,
Wherein the data modulator further comprises an analog-to-digital converter connected between the thermistor and the selection unit.
The method according to claim 6,
Wherein the selecting unit modulates the blue image data by comparing the data received from the thermistor with data of the memory unit to generate the modulated blue image data and transmits the modulated blue image data to the data driver.

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