KR100590106B1 - A liquid crystal display and a driving method thereof - 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.

A liquid crystal display device according to the present invention comprises: 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; 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, wherein a light source displaying a color among the light sources is normally emitted, and a light source not displaying a color is driven to generate heat as long as light emission does not occur. do.

According to the present invention, when the temperature or ambient temperature of the liquid crystal panel is detected as a low temperature, the light sources that do not display color are heated in a range where no light is emitted, thereby supplying predetermined heat to the panel, thereby increasing the temperature of the liquid crystal panel above room temperature. It can be maintained as, thereby preventing the problem of low color reproduction rate 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.

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") instead of cathode ray tubes (CRTs) are required. 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 (FIG. 1). The liquid crystal adjusts the transmittance of light in response to the intensity of the applied electric field, and the storage capacitor Cst converts 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 by using the afterimage effect of the eyes by sequentially displaying time-divisionally the light of three primary colors supplied from each backlight.

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;

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

Including but not limited to:

Among the light sources, a light source displaying color is normally operated to emit light, and a light source not displaying color is driven to generate heat as long as light emission does not occur.

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

A method of driving a sequential drive type liquid crystal display device having at least three light sources for backlight,

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

b) applying a light emission driving current or a light emission driving voltage to a light source for displaying color to output corresponding light;

c) applying a heating driving current or a heating driving voltage to a light source that does not display color when the sensed temperature is lower than a predetermined temperature; And

d) supplying predetermined heat to the liquid crystal panel by heating a light source not displaying the color according to the exothermic driving current or the exothermic driving voltage;

It includes.

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 that do not display color are heated in a range where no light is emitted to supply predetermined heat to the liquid crystal panel, whereby the liquid crystal display apparatus has a low temperature. Will work stably.

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.

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 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 driving voltage to the light sources 800R, 800G, and 800B when a control signal is supplied from the temperature sensor 900. When a driving voltage is supplied to the light sources 800R, 800G, and 800B, heat is generated from the light sources 800R, 800G, and 800B to prevent the temperature of the liquid crystal panel 100 from falling below a predetermined temperature. As a result, the light source controller 700 simultaneously controls emission and heat generation.

For example, in an exemplary embodiment of the present invention, when the temperature of the liquid crystal panel is lower than or equal to a predetermined temperature, an LED (for example, a red LED) for displaying a color operates normally by applying a driving current and does not display a color. Other LEDs (e.g., green LEDs and blue LEDs) that do not have a small current smaller than the driving current (a current that does not completely light up the liquid crystal) are applied to heat the LEDs to supply predetermined heat to the liquid crystal panel. do.

As described above, when the panel temperature drops 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 maintained at a temperature higher than 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, in the embodiment of the present invention as a method of driving a sequential driving type liquid crystal display device having at least three light sources for the backlight, first, to detect the temperature or the ambient temperature of the liquid crystal panel, and then display the color A light emission driving current or a light emission driving voltage is applied to the light source for outputting the corresponding light.

Next, when the detected temperature is less than the predetermined temperature range of 10 ° C and 25 ° C, a heating driving current or a heating driving voltage is applied to a light source that does not display color, and the color according to the heating driving current or heating driving voltage. By heating a light source that does not display the predetermined heat is supplied to the liquid crystal panel.

Meanwhile, in the embodiment of the present invention, the temperature may be divided into a plurality of temperature levels, and different driving voltages may be supplied for each temperature level. In detail, the temperature sensor 900 supplies different control signals to the light source controller 700 for each preset temperature level. For example, the temperature sensor 900 may output a control signal of “0000” when the temperature of the liquid crystal panel 100 and the ambient temperature of the liquid crystal panel 100 are higher than room temperature (eg, 25 ° C.). To supply. In addition, the temperature sensor 900 has a different control signal for each preset temperature level when the temperature of the panel 100 and the ambient temperature of the panel 100 are less than room temperature, that is, the control signals of “0001” to “1111”. Is supplied to the light source control unit 700. The light source controller 700 supplies a driving voltage having a different voltage value for each temperature level to the light sources 800R, 800G, and 800B in response to a control signal supplied from the temperature sensor 900. Here, the light source controller 700 supplies a driving voltage having a higher voltage value to the light sources 800R, 800G, and 800B 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 that is proportional to the voltage value of the 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 the heat is generated and supplied to the panel 100.

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 to each other. Accordingly, as described above, various exothermic driving currents or driving voltages may be applied according to the temperature level sensed by the temperature sensor. Is generated and 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, it is shown that a heating current or a heating driving voltage smaller than the driving current or driving voltage expressing the color is applied to the light source not expressing the color, and thus the light source generates heat. As described above, the exothermic driving current or the exothermic driving voltage is provided less than the value that the light source can normally emit, and thus only generates heat rather than emitting light. In addition, since the red, green, and blue light sources emit light sequentially, when the temperature or the ambient temperature of the liquid crystal panel detected by the temperature sensor is lower than a predetermined temperature, when one light source emits light, the other light source generates heat. This operation is repeatedly performed until the temperature or ambient temperature of the liquid crystal panel sensed by the temperature sensor is above a predetermined temperature.

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 of the liquid crystal panel or the ambient temperature of the liquid crystal panel is detected as a low temperature, by supplying a predetermined heat to the liquid crystal panel by using light sources that do not display color, the temperature of the liquid crystal panel above a predetermined temperature It can be maintained as, thereby preventing the problem of low color reproduction rate at low temperatures.

Claims (12)

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; 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 Including but not limited to: A light source displaying color among the light sources is normally light-emitted, and a light source not displaying color is driven by heat generation as long as light emission does not occur. The method of claim 1, Wherein the exothermic driving current or the exothermic driving voltage is smaller than the driving current or driving voltage at which the light source normally emits light. 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 ℃. The method of claim 1, And the temperature sensor determines which temperature level among the plurality of temperature levels, and outputs a different control signal for each of the determined temperature levels. The method of claim 5, And the light source controller provides a heat generating driving current or a heat generating driving voltage to the light source in which a light source that does not display the color generates more heat as the temperature level decreases. A method of driving a sequential drive type liquid crystal display device having at least three light sources for backlight, a) sensing the temperature or ambient temperature of the liquid crystal panel; b) applying a light emission driving current or a light emission driving voltage to a light source for displaying color to output corresponding light; c) applying a heating driving current or a heating driving voltage to a light source that does not display color when the sensed temperature is lower than a predetermined temperature; And d) supplying predetermined heat to the liquid crystal panel by heating a light source not displaying the color according to the exothermic driving current or the exothermic driving voltage; Method of driving a liquid crystal display of a field sequential driving method comprising a. The method of claim 7, wherein And a heat generating driving current or a heat generating driving voltage is applied to a light source that does not display the color of step c) in a range in which light emission does not occur. The method of claim 7, wherein And wherein the exothermic driving current or the exothermic driving voltage is smaller than the driving current or driving voltage at which the light source normally emits light. The method of claim 7, wherein And at least three or more light sources are backlight LEDs. The method of claim 7, wherein Determining which temperature level among the plurality of temperature levels corresponds to the temperature detected in step a); And Supplying a heating driving current or a heating driving voltage corresponding to the determined temperature level to the light source. Method of driving a liquid crystal display of a field sequential driving method comprising a. The method of claim 11, And the lower the temperature level, the higher the value of the heating driving current or the heating driving voltage is set.

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