KR100599731B1 - LCD and its driving method - Google Patents

Abstract

The present invention relates to a field-sequential driving type liquid crystal display device and a driving method thereof capable of stable operation at low temperatures. The liquid crystal display device of the present invention includes a temperature sensor, a light source and a light source controller. The temperature sensor senses the temperature or the ambient temperature of the liquid crystal panel and outputs a control signal for a time corresponding to the level of the sensed temperature. The light source controller controls light emission or heat generation of the light source according to the control signal. The light source generates heat by applying a transient driving current or transient driving voltage larger than a normal driving current or driving voltage representing a color. According to the present invention, when the temperature or the ambient temperature of the liquid crystal panel is detected at a low temperature, the light sources are heated with a transient driving current or driving voltage higher than the light emitting driving current or driving voltage representing the color to supply predetermined heat to the liquid crystal panel. The temperature of the liquid crystal panel can be maintained at or above room temperature, thereby preventing the problem of low color reproducibility at low temperatures.

LCD, Heat source, LED, Temperature sensor, Field sequential drive, Backlight

Description

Liquid Crystal Display and Driving Method {A LIQUID CRYSTAL DISPLAY AND A DRIVING METHOD THEREOF}

1 is a view showing a pixel of a conventional liquid crystal display device.

2 is a diagram illustrating a liquid crystal display device according to an exemplary embodiment of the present invention.

3 is a view showing the relationship between the forward current (voltage) and the brightness of the LED according to an embodiment of the present invention.

4 is a view for explaining a method of driving a liquid crystal display according to an exemplary embodiment of the present invention.

5 is a view for explaining a method of driving a liquid crystal display according to another exemplary embodiment of the present invention.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device and a driving method thereof, and more particularly, to a liquid crystal display device having a field sequential driving method capable of stable operation at low temperature and a driving method thereof.

Recently, display devices are also required to be lighter and thinner in accordance with the light weight and thickness of personal computers and televisions, and according to such demands, liquid crystal displays ("LCD") are used instead of cathode ray tubes (CRT). Flat panel displays are being developed.

The LCD applies an electric field to a liquid crystal material having an anisotropic dielectric constant injected between two substrates, and adjusts the intensity of the electric field to transmit the amount of light transmitted from the external light source (back-light) to the substrate. By adjusting the desired image is obtained.

Such LCDs are typical of portable flat panel displays, and among them, TFT-LCDs using thin film transistors (hereinafter referred to as TFTs) as switching elements are mainly used.

Therefore, in the TFT-LCD, each pixel may be modeled as a liquid crystal capacitor because electrodes (pixel electrodes and common electrodes) are disposed to face each other with a liquid crystal interposed therebetween. In such LCDs, each pixel is an equivalent circuit as shown in FIG. It may be represented as.

As shown in Fig. 1, each pixel of the liquid crystal display according to the prior art includes: a TFT 10 having a source electrode connected to a data line Dm and a gate electrode connected to a scan line Sn; A liquid crystal capacitor Cl connected between the drain electrode of the TFT 10 and the common electrode Vcom; And a storage capacitor Cst connected to the drain electrode of the TFT 10.

The TFT 10 provides the pixel electrode (not shown) with the data voltage Vd supplied from the data line Dm in response to the scan signal from the scan line Sn. The electric field corresponding to the difference between the data voltage provided to the pixel electrode (that is, the pixel voltage Vp and the common voltage Vcom applied to the common electrode (not shown) is equivalent to that of the liquid crystal capacitor (FIG. 1). The liquid crystal adjusts the transmittance of light in response to the intensity of the applied electric field.The storage capacitor Cst uses the pixel voltage provided to the liquid crystal capacitor Cl to the next data voltage Vd. The light is transmitted for a predetermined time by maintaining it until it is supplied.

In general, the LCD may be divided into two methods, a color filter method and a field sequential driving method, according to a method of displaying a color image.

The color filter LCD forms a color filter layer consisting of three primary colors of red (R), green (G) and blue (B) on the upper substrate of the panel, and adjusts the amount of light transmitted through the color filter layer. The desired image is displayed. However, the color filter type LCD requires unit pixels corresponding to each of the red (R), green (G), and blue (B) regions, and thus requires three times as many pixels as those for displaying black and white. Therefore, in order to obtain high resolution images, sophisticated manufacturing technology of LCD panels is required. In addition, in the color filter LCD, red (R), green (G), and blue (B) color filters must be formed on the upper substrate, which is cumbersome in manufacturing, and the light transmittance of the color filter itself must be improved. There is a problem.

In addition, the LCD of the field sequential driving method periodically turns on independent light sources of red (R), green (G), and blue (B) colors sequentially, and supplies pixel voltages (Vp) to the pixels for each of the lighting cycles. Displays a color image. That is, a field-sequential driving LCD does not divide one pixel into unit pixels of red (R), green (G), and blue (B), and red (R), green (G), and blue colors in one pixel. (B) Color images are displayed using the afterimage effect of the eyes by sequentially displaying the light of the three primary colors supplied from each backlight in time division.

The field sequential driving method can be classified into an analog driving method and a digital driving method.

The analog driving method sets a plurality of gray voltages corresponding to the number of gray scales to be displayed, selects one gray voltage corresponding to gray data among the gray voltages, and drives the liquid crystal panel with the selected gray voltage, thereby applying the applied gray voltage. Gradation display is performed with the amount of transmitted light corresponding to.

In addition, the digital driving method makes the driving voltage applied to the liquid crystal constant and controls the voltage application time to perform gradation display. According to this digital driving method, the gray scale is displayed by adjusting the accumulated amount of light transmitted through the liquid crystal by maintaining the driving voltage constant and controlling the voltage-applied state and the voltage-unapplied state in a timely manner.

On the other hand, since the above-described field sequential driving LCD drives one frame into an R field, a G field, and a B field, the liquid crystal should have a higher response speed than the color filter LCD. However, the lower the temperature, the lower the response speed of the liquid crystal. Therefore, when the field sequential driving LCD is used for a portable device (for example, a mobile phone) that is frequently exposed to a low temperature environment, the response speed of the liquid crystal is lowered and the color reproducibility is reduced. There was a problem of being lowered.

 An object of the present invention for solving the above problems is to provide a field-sequential driving type liquid crystal display device and a driving method thereof capable of stable operation at low temperatures.

As a means for achieving the above object, the liquid crystal display device according to the present invention,

A liquid crystal panel having an upper substrate and a lower substrate; A temperature sensor for sensing a temperature or an ambient temperature of the liquid crystal panel and outputting a control signal for a time corresponding to the level of the detected temperature; The light of red (R), green (G) and blue (B) is sequentially output to each pixel arranged in the liquid crystal panel, and when the temperature detected by the temperature sensor is less than a predetermined temperature, the liquid crystal panel is heated. At least three light sources for making; And a light source controller for controlling light emission or heat generation of the light source according to the control signal.

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Including but not limited to:

The light source may generate heat by applying an excessive driving current or an excessive driving voltage larger than a normal driving current or driving voltage representing a color.

In addition, as another means for achieving the above object, the driving method of the liquid crystal display device according to the present invention,

In the method for driving a liquid crystal display device having a plurality of light sources,

a) sensing the temperature or ambient temperature of the liquid crystal panel;

b) comparing the detected temperature with a predetermined temperature, and determining a heat generation or emission time corresponding to the level of the sensed temperature according to the comparison result;
c) heating the light source by generating a heating driving current or a heating driving voltage during the heating or emitting time; And
d) a predetermined heat is supplied from the heated light source to the liquid crystal panel

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It includes.

According to the present invention, when the temperature or the ambient temperature of the liquid crystal panel is detected as a low temperature, by heating the light sources with a transient driving current or driving voltage higher than the light emitting driving current or driving voltage representing the color by supplying a predetermined heat to the liquid crystal panel The temperature of the liquid crystal panel can be maintained at room temperature or higher.
DETAILED DESCRIPTION Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the present invention. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention. In the drawings, parts irrelevant to the description are omitted in order to clearly describe the present invention. Like parts are designated by like reference numerals throughout the specification.

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2 is a view showing a liquid crystal display (LCD) according to an embodiment of the present invention.

2, the LCD according to an embodiment of the present invention includes a panel 100, a scan driver 300, a data driver 400, a gray voltage generator 500, a timing controller 600, and at least three or more LCDs. Light sources 800R, 800G, and 800B, a light source controller 700 and a temperature sensor 900 are provided. Here, the light sources 800R, 800G, and 800B use a light emitting diode (LED) for backlight of the liquid crystal panel.

The panel 100 includes a plurality of pixels 120 arranged in a matrix at the intersection of the scan line S and the data line D. FIG.

The timing controller 600 receives the gray level data signals R, G, and B data, the horizontal synchronization signal Hsync, and the vertical synchronization signal Vsync from an external or graphic controller (not shown), and scan scan unit 300. ), A scan control signal Sg for controlling the control panel, a data control signal Sd for controlling the data driver 400, and a light source control signal Sb for controlling the light source controller 700. The timing controller 600 supplies the gray data signals R, G, and B data to the gray voltage generator 500.

The scan driver 300 selects a horizontal line to which the data voltage Vd is supplied by sequentially supplying a scan signal to the scan line S in response to the scan control signal Sg supplied from the timing controller 600.

The gray voltage generator 500 generates a gray voltage (data voltage Vd) corresponding to the gray data signals R, G, and B DATA, and converts the generated data voltage Vd to the data driver 400. Supply. The data driver 400 supplies the data voltage Vd to the data line D while being controlled by the data control signal Sd.

The light source controller 700 may emit the light sources 800R, the green light sources 800R, the blue light sources 800G, and the blue light sources 800B in different periods of one frame in response to the light source control signal Sb. 800G, 800B). In this case, driving currents I _R , I _G , and I _B expressing colors are supplied to the light sources 800R, 800G, and 800B, and the temperature or the ambient temperature of the liquid crystal panel detected by the temperature sensor 900 is When the temperature is lower than the predetermined temperature, the transient driving currents H _R , H _G and H _B are supplied. In the embodiment of the present invention, a light emitting diode (LED) is used as the light emitting and heat generating light sources, but the present invention is not limited thereto.

The temperature sensor 900 detects the temperature of the liquid crystal panel 100 or the ambient temperature T of the liquid crystal panel. When the temperature or the ambient temperature of the liquid crystal panel 100 is sensed below a predetermined temperature (in the embodiment of the present invention, the predetermined temperature is set to a temperature between 10 ° C and 25 ° C), the temperature sensor 900 controls the control signal ( S _T ) is generated and supplied to the light source controller 700. The light source controller 700 supplies a transient driving current H _R , H _G , H _B or a driving voltage to the light sources 800R, 800G, and 800B when a control signal is supplied from the temperature sensor 900. When a transient driving current (H _R , H _G , H _B ) or a driving voltage is supplied to the light sources 800R, 800G, and 800B, heat is generated from the light sources 800R, 800G, and 800B, so that the liquid crystal panel 100 ) Temperature is prevented from falling below a predetermined temperature.

Specifically, in the exemplary embodiment of the present invention, when the temperature of the liquid crystal panel 100 is less than or equal to a predetermined temperature, the liquid crystal panel does not operate properly for a predetermined period of time, so that a transient current or transient higher than a driving current or a driving voltage to operate normally. By driving the voltage, the liquid crystal panel is heated by heating the LED which is the light source. In particular, in a situation where the liquid crystal panel does not operate properly anyway, the electric current is induced to be converted into the thermal energy from the liquid crystal by dissipating the light energy as much as possible without breaking the characteristics of the light source element.

As described above, when the temperature of the panel decreases below a predetermined temperature, the panel is independent of the ambient temperature T because the light source controller 700 drives the exothermic light source to heat the liquid crystal panel 100. It is always kept above a predetermined temperature. Therefore, since the liquid crystal contained in the panel 100 maintains a response speed higher than or equal to a predetermined level, reliability of the LCD may be secured.

On the other hand, the method for driving a liquid crystal display device having a plurality of light sources according to an embodiment of the present invention, first sensing the temperature or the ambient temperature of the liquid crystal panel, and if the detected temperature is less than a predetermined temperature, excessive driving to the light source Current or transient driving voltage is applied. Thereafter, the light source is heated according to the transient driving current or the transient driving voltage to supply predetermined heat to the liquid crystal panel. In this case, the transient driving current or the transient driving voltage causes the light source to generate heat within the limit that the device characteristics of the light source are not destroyed.

On the other hand, in the embodiment of the present invention, the temperature may be divided into a plurality of temperature levels, and the driving voltage may be supplied for a different time for each temperature level. In detail, the temperature sensor 900 supplies a control signal to the light source controller 700 for a different time for each preset temperature level. For example, when the temperature of the liquid crystal panel 100 and the ambient temperature of the liquid crystal panel 100 are higher than room temperature (for example, 25 ° C.), the temperature sensor 900 transmits a control signal of “0000” to the light source controller 700. ). In addition, when the temperature of the panel 100 and the ambient temperature of the panel 100 are lower than room temperature, the temperature sensor 900 transmits a control signal of “1111” for a different time for each preset temperature level to the light source controller 700. ). The light source control unit 700 supplies the transient driving voltage to the light sources 800R, 800G, and 800B for a different time at each temperature level in response to the time when the control signal supplied from the temperature sensor 900 is applied. Here, the light source controller 700 supplies the transient driving voltage to the light sources 800R, 800G, and 800B for a longer time as the control signal supplied from the temperature sensor 900 corresponds to a low temperature level. The light sources 800R, 800G, and 800B generate heat in proportion to the time of the transient driving voltage supplied thereto, and supply the heat to the panel 100. That is, in the embodiment of the present invention, as the temperature sensed by the temperature sensor 900 decreases, the panel 100 may be stably driven because heat is generated and supplied to the panel 100 for a long time.

3 is a diagram illustrating a relationship between a forward current (voltage) and brightness of an LED according to an exemplary embodiment of the present invention. When the forward current or voltage is applied to the LED, the light source described above, the LED corresponds to the brightness of the corresponding LED. Luminous Flux is almost linearly proportional, and accordingly, as described above, the transient driving current or the driving voltage may be applied according to the temperature level detected by the temperature sensor, and thus heat is generated from the light source. The liquid crystal panel is supplied to the liquid crystal panel, and eventually, the heating at the low temperature can be improved by heating the liquid crystal panel.

On the other hand, Figure 4 is a view for explaining a driving method of the liquid crystal display according to an embodiment of the present invention, when the temperature or ambient temperature of the liquid crystal panel detected by the temperature sensor is lower than the predetermined temperature, each of the red, green and In the blue LED, the transient heating current or the heating driving voltage higher than the driving current or driving voltage expressing the color is applied to the light source, and thus the light source generates heat. Such an operation is performed for a predetermined time until the temperature reaches a predetermined temperature or more according to the temperature or ambient temperature of the liquid crystal panel detected by the temperature sensor.

FIG. 5 is a view for explaining a method of driving a liquid crystal display according to another exemplary embodiment of the present invention, wherein the transient driving current or the transient driving voltage may be applied to the light source within a range in which device characteristics of the light source are not destroyed. In other words, the light source is operated in a range larger than the driving current or driving voltage representing the color and smaller than the maximum driving current or driving voltage at which the characteristics of the light source element are destroyed.

In this case, the time for which the transient driving current or the transient driving voltage is applied depends on the temperature or the ambient temperature of the liquid crystal panel. When the liquid crystal panel becomes above room temperature, the application of the transient driving current or the transient driving voltage is stopped. In addition, a driving current or a driving voltage to which the light source normally expresses color is applied.

Although the embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements of those skilled in the art using the basic concepts of the present invention defined in the following claims are also provided. It belongs to the scope of rights.

For example, in the above-described embodiment of the present invention, the LCD of the field sequential driving method has been described as an example, but may be applied to various LCDs other than the field sequential driving LCD.

According to the present invention, when the temperature or the ambient temperature of the liquid crystal panel is detected at a low temperature, the light sources are heated with a transient driving current or driving voltage higher than the light emitting driving current or driving voltage representing the color to supply predetermined heat to the liquid crystal panel. The temperature of the liquid crystal panel may be maintained at room temperature or higher, thereby preventing the problem of low color reproducibility at low temperatures.

Claims (13)

A liquid crystal panel having an upper substrate and a lower substrate; A temperature sensor for sensing a temperature or an ambient temperature of the liquid crystal panel and outputting a control signal for a time corresponding to the level of the sensed temperature; The light of red (R), green (G) and blue (B) is sequentially output to each pixel arranged in the liquid crystal panel, and when the temperature detected by the temperature sensor is less than a predetermined temperature, the liquid crystal panel is heated. At least three light sources for making; And A light source controller for controlling light emission or heat generation of the light source according to the control signal Including but not limited to: And the light source generates heat by applying an excessive driving current or an excessive driving voltage larger than a normal driving current or driving voltage representing a color. The method of claim 1, Wherein the transient driving current or the transient driving voltage generates the light source within a limit in which element characteristics of the light source are not destroyed. The method of claim 1, And the light source is a backlight light emitting diode (LED) of the liquid crystal panel. The method of claim 1, The predetermined temperature is a liquid crystal display device, characterized in that the temperature between 10 ℃ to 25 ℃. delete The method of claim 1, And the light source controller provides a transient driving current or a transient driving voltage to the light source for more time as the temperature level decreases. In the method for driving a liquid crystal display device having a plurality of light sources, a) sensing the temperature or ambient temperature of the liquid crystal panel; b) comparing the detected temperature with a predetermined temperature, and determining a heat generation or emission time corresponding to the level of the sensed temperature according to the comparison result; c) heating the light source by generating a heating driving current or a heating driving voltage during the heating or emitting time; d) a predetermined heat is supplied from the heated light source to the liquid crystal panel Liquid crystal display driving method comprising a. The method of claim 7, wherein Wherein the exothermic driving current or the exothermic driving voltage of step c) generates the light source within a range in which element characteristics of the light source are not destroyed. The method of claim 7, wherein And the light source generates heat by applying an excessive driving current or an excessive driving voltage larger than a normal driving current or driving voltage representing a color. The method of claim 7, wherein And the plurality of light sources are backlight LEDs. delete The method of claim 7, wherein In step c), The lower the temperature level is, the longer the time for which the heating driving current or the heating driving voltage is applied is set. The method of claim 7, wherein In step b), And a result of determining the heating or emitting time corresponding to the level of the detected temperature when the detected temperature is lower than the predetermined temperature.

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