KR100684713B1 - A liquid crystal display and a driving method thereof - Google Patents

Abstract

The present invention relates to a liquid crystal display and a driving method thereof.

According to the present invention, a liquid crystal is formed between a first substrate on which a first electrode is disposed and a second substrate on which a second electrode is disposed, and a light source sequentially transmits red, green, and blue light to one pixel. In the liquid crystal display device, a plurality of voltages for driving the light source are generated, and after the temperature is measured, a voltage corresponding to the measured temperature is selected and supplied to the light source. In particular, as the temperature decreases, the driving voltage of the red light source is increased. By doing so, it is possible to compensate for the luminance of the LED lowered at low temperatures and to balance the white balance.

Field sequential, FS, LCD, light source, LED

Description

Liquid crystal display and its driving method {A LIQUID CRYSTAL DISPLAY AND A DRIVING METHOD THEREOF}

1 is a view showing a pixel of a conventional TFT-LCD.

2 is a waveform diagram illustrating a driving method of a conventional analog liquid crystal display device.

3 is a waveform diagram illustrating a driving method of a conventional digital liquid crystal display device.

4 is a view illustrating a change in luminance for each temperature of a conventional liquid crystal display device.

5 is a view illustrating a change in color coordinates for each temperature of a conventional liquid crystal display device.

6 illustrates 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 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. Panel-type displays are being developed.

An 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 control the amount of light transmitted to the substrate from an external light source (backlight). A display device for obtaining an image signal.

Such LCDs are typical of portable flat panel displays, and among them, TFT-LCD using a thin film transistor (TFT) as a switching element is mainly used.

In the TFT-LCD, each pixel may be modeled as a capacitor having a liquid crystal as a dielectric, that is, a liquid crystal capacitor. The equivalent circuit of each pixel in the LCD is shown in FIG.

As shown in FIG. 1, each pixel of the liquid crystal display includes a TFT 10 having a source electrode and a gate electrode connected to the data line Dm and the scan line Sn, respectively, a drain electrode of the TFT, and a common voltage Vcom. It includes a liquid crystal capacitor (Cl) connected between and a storage capacitor (Cst) connected to the drain electrode of the TFT.

In Fig. 1, when the scan signal is applied to the scan line Sn and the TFT 10 is turned on, the data voltage Vd supplied to the data line is applied to each pixel electrode (not shown) through the TFT. Then, an electric field corresponding to the difference between the pixel voltage Vp and the common voltage Vcom applied to the pixel electrode is applied to the liquid crystal (equivalently represented by the liquid crystal capacitor in FIG. 1), and thus transmittance corresponding to the intensity of the electric field. To allow light to pass through. At this time, the pixel voltage Vp should be maintained for one frame or one field. In FIG. 1, the storage capacitor Cst is used to maintain the pixel voltage Vp applied to the pixel electrode.

In general, the liquid crystal display 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.

A color filter type liquid crystal display device forms a color filter layer composed of three primary colors of red (R), green (G), and blue (B) on one of two substrates, and transmits the amount transmitted through the color filter layer. Display the desired color by adjusting. The color filter type LCD synthesizes R, G, and B colors by adjusting the amount of light transmitted through the R, G, and B color filter layers to transmit light emitted from a single light source to the R, G, and B color filter layers. Thereby displaying the desired color.

As described above, in a liquid crystal display device displaying a color using a single light source and a three-color color filter layer, a corresponding unit pixel is required for each of the R, G, and B regions, so that three times as many pixels are used as for displaying black and white. It is necessary. Therefore, in order to obtain a high resolution image, sophisticated manufacturing technology of a liquid crystal display panel is required.

In addition, there is a manufacturing problem that a separate color filter layer must be formed on the liquid crystal display substrate, and there is a problem that the light transmittance of the color filter itself must be improved.

The liquid crystal display of the field sequential driving method sequentially turns on independent light sources of R, G, and B colors, and applies a color signal corresponding to each pixel in synchronization with the lighting cycle to display a full color image. Get it. That is, according to the liquid crystal display of the field sequential driving method, R, G, and B primary colors output from R, G, and B backlights to one pixel are not divided into R, G, and B pixel units. By displaying the light sequentially in time division, a color image is displayed using the afterimage effect of the eye.

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.

2 is a diagram illustrating a driving voltage and a transmitted light amount according to a conventional LCD driving apparatus.

Referring to FIG. 2, in the R field section Tr for displaying the R color, a driving voltage of the V11 level is applied to the liquid crystal so that light corresponding to the driving voltage of the V11 level passes through the liquid crystal. In the G field section Tg for displaying the G color, a driving voltage of the V12 level is applied so that light corresponding to the driving voltage of the V12 level passes through the liquid crystal. Then, in the B field section Tb for displaying the B color, a driving voltage of the V13 level is applied to obtain a light transmittance corresponding to the driving voltage of the V13 level. The desired color image is displayed by the sum of the R, G, and B lights transmitted in the Tr, Tg, and Tb sections, respectively.

On the other hand, 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 keeping the driving voltage constant and controlling the voltage applied state and the voltage unapplied state in a timely manner.

FIG. 3 is a waveform diagram illustrating a conventional method for driving a liquid crystal display device of a digital driving method, and illustrates a waveform of a driving voltage according to driving data of a predetermined bit and a waveform of an amount of light passing through the liquid crystal. will be.

Referring to FIG. 3, grayscale waveform data corresponding to each grayscale is provided as a digital signal of a predetermined bit, for example, 7bit, and a grayscale waveform according to the 7bit data is applied to the liquid crystal. Then, the transmission amount of the liquid crystal is determined according to the applied gradation waveform to perform gradation display.

On the other hand, the LED used as a light source of the liquid crystal display device has a problem that the brightness is lowered at low temperatures, and not only white balance but also color reproducibility.

This is as follows.

4 is a view showing a change in luminance for each temperature of a conventional LED.

Referring to FIG. 4, as the temperature decreases, the luminance changes, and in particular, the luminance of the red (R) component decreases.

5 is a view showing a change in color coordinates for each temperature of a conventional LED.

Referring to FIG. 5, the lower the temperature, the more the coordinate change occurs for each temperature. In particular, it can be seen that the change of the X coordinate component in which the red component is much related is large.

As described above, the LEDs used in the conventional liquid crystal display have a problem in that the luminance is lowered at low temperatures, and the color reproducibility is lowered as well as the white balance.

SUMMARY OF THE INVENTION The present invention has been made in an effort to solve the problems of the related art, and a liquid crystal display device and a method of driving the same, which compensate for a reduced luminance by changing a driving voltage of an LED light source according to temperature and adjust a white balance. To provide.

According to one aspect of the present invention for achieving the above object, a liquid crystal display device,
A liquid crystal display comprising a liquid crystal formed between a first substrate on which a first electrode is disposed and a second substrate on which a second electrode is disposed, and sequentially transmitting red, green, and blue light to one pixel.
A light source sequentially outputting red, green, and blue light to one pixel based on each driving voltage;
A temperature sensor for measuring a temperature;
A memory for storing a driving voltage of the light source corresponding to each temperature;
A voltage generator configured to generate a plurality of driving voltages for driving the light source; And
And a driving voltage controller configured to determine a driving voltage corresponding to the temperature sensed by the temperature sensing unit with reference to the memory and to supply the determined driving voltage from the voltage generator to the light source.
A driving method of a liquid crystal display device according to an aspect of the present invention for achieving the above object,
And a liquid crystal formed between the first substrate on which the first electrode is disposed and the second substrate on which the second electrode is disposed, wherein the light source sequentially transmits red, green, and blue light to one pixel. As a driving method,
Generating a plurality of driving voltages corresponding to respective temperatures and for driving the light sources;
A second step of measuring the temperature; And
And selecting a driving voltage corresponding to the measured temperature and supplying the driving voltage to the light source.

delete

delete

delete

delete

delete

delete

delete

delete

delete

delete

delete

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.

The term "reset" described below means applying a voltage (or waveform) to make the liquid crystal material in the LCD black, which cannot transmit light. In addition, the 'gradation voltage' refers to a voltage having different voltage levels.

Next, a liquid crystal display according to an exemplary embodiment of the present invention will be described with reference to FIG. 6.

FIG. 6 is a diagram illustrating a liquid crystal display according to an exemplary embodiment of the present invention, and a dotted line in FIG. 6 represents a flow of power.

As shown in FIG. 6, the liquid crystal display according to the exemplary embodiment of the present invention includes a liquid crystal display panel 100, a scan driver 200, a data driver 300, a gray voltage generator 500, and a timing controller ( 400, light emitting diodes 600a, 600b, and 600c that output R, G, and B light sources, light source controller 700, temperature sensing unit 900, driving low voltage control unit 800, voltage generating unit 1000, and Memory 1100.

A plurality of scan lines are formed on the liquid crystal display panel 100 to transmit a gate-on signal, and the plurality of scan lines are insulated from and intersect with the plurality of scan lines, and the data lines are configured to transmit gray data voltages and reset voltages corresponding to gray data. Formed. The plurality of pixels 110 arranged in a matrix form are surrounded by scan lines and data lines, respectively. Each pixel includes a thin film transistor (not shown) having a gate electrode and a source electrode connected to the scan line and a data line, a pixel capacitor (not shown), and a storage capacitor (not shown) connected to the drain electrode of the thin film transistor. do. The liquid crystal display panel 100 includes a liquid crystal (not shown) formed between a first substrate on which a first electrode is disposed and a second substrate on which a second electrode is disposed, and a predetermined amount of dopant is added to the liquid crystal. In addition to lower the chiral pitch to a specific state.

The gate driver 200 sequentially applies a scan signal to the scan line, thereby turning on the TFT to which the gate electrode is connected to the scan line to which the scan signal is applied.

The timing controller 400 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 controls necessary signals Sg, Sd and Sb are supplied to the scan driver 200, the data driver 300, and the light source controller 700, respectively, and the gray scale data R, G, and B DATA are supplied to the gray voltage generator 500.

The gray voltage generator 500 generates a gray voltage having a magnitude corresponding to gray data and supplies it to the data driver 300. The data driver 300 applies the gray voltage output by the gray voltage generator 500 to the data line in the gray bit period, and applies a reset voltage to the data line to reset the data in the reset period. do.

The light emitting diodes 600a, 600b, and 600c respectively output light corresponding to R, G, and B to the LCD panel 100 during the lighting period, and the light source controller 700 turns on the light emitting diodes 600a, 600b, and 600c. Control the timing.

In this case, the timing at which the gray level voltage is supplied or stopped from the data driver 300 to the data line and the timing at which the R, G, and B light emitting diodes are turned on by the light source controller 800 are controlled by the timing controller 500. Can be synchronized by a signal.

On the other hand, the temperature sensing unit 900 measures and outputs a temperature as a temperature sensor. The memory 1100 stores the driving voltage look-up table of the light emitting diodes 600a, 600b, and 600c corresponding to the temperature, and the value of the light emitting diode 600a emitting red light may vary depending on the temperature. Therefore, the lower the temperature, the higher the driving voltage. If necessary, the driving voltages of the other light emitting diodes 600b and 600c may vary only in accordance with the temperature in order to save memory and simplify and reduce costs. Such a lookup table calculates and stores a suitable driving voltage at a corresponding low temperature by experiment.

In addition, the voltage generator 100 generates a plurality of voltages for driving the light sources, that is, the light emitting diodes 600a, 600b, and 600c.

Then, the driving voltage controller 800 determines a voltage corresponding to the temperature sensed by the temperature sensing unit 900 with reference to the memory 1100, and determines the determined voltage from the voltage generating unit as the light emitting diode ( Control to supply 600a, 600b, 600c).

By this process, even when the temperature is low, the luminance is compensated by driving the light emitting diodes 600a, 600b, and 600c with a driving voltage corresponding thereto, and white balance can be achieved.

Although the above has been described with reference to embodiments of the present invention, those skilled in the art will be able to variously modify and change the present invention without departing from the spirit and scope of the invention as set forth in the claims below. It will be appreciated.

 As described above, according to the present invention, the driving voltage of the LED light source may be changed according to temperature, thereby compensating for the reduced luminance, adjusting the white balance, and improving the color reproducibility.

Claims (9)

A liquid crystal display comprising a liquid crystal formed between a first substrate on which a first electrode is disposed and a second substrate on which a second electrode is disposed, and sequentially transmitting red, green, and blue light to one pixel. A light source sequentially outputting red, green, and blue light to one pixel based on each driving voltage; A temperature sensor for measuring a temperature; A memory for storing a driving voltage of the light source corresponding to each temperature; A voltage generator configured to generate a plurality of driving voltages for driving the light source; And A driving voltage controller configured to determine a driving voltage corresponding to the temperature sensed by the temperature sensing unit with reference to the memory, and to control the driving voltage to be supplied from the voltage generator to the light source; The driving voltage of the light source is higher as the temperature is lower, the liquid crystal display device. The method of claim 1, The light source is, A red light emitting diode emitting red light; A green light emitting diode emitting green light; A liquid crystal display comprising a blue light emitting diode emitting blue light. The method of claim 2, And the memory stores a driving voltage of the red light emitting diode, a driving voltage of the green light emitting diode, and a driving voltage of the blue light emitting diode corresponding to a temperature. The method of claim 2, And the memory stores a driving voltage of the red light emitting diode corresponding to a temperature. The method according to claim 3 or 4, A matrix form having a plurality of scan lines for transmitting a scan signal, a plurality of data lines insulated from and intersecting the scan lines, a switching element formed in an area surrounded by the scan lines and data lines, and connected to the scan lines and data lines, respectively. A liquid crystal display panel including a plurality of pixels arranged in a line; A gate driver for sequentially supplying scan signals to the scan lines; A gray voltage generator which generates a gray voltage corresponding to gray data; And a data driver for supplying a gradation voltage output from the gradation voltage generator and a reset pulse for initializing the state of the liquid crystal to a specific state. The method of claim 1, And the temperature sensing unit senses a temperature inside the liquid crystal display panel. And a liquid crystal formed between the first substrate on which the first electrode is disposed and the second substrate on which the second electrode is disposed, wherein the light source sequentially transmits red, green, and blue light to one pixel. As a driving method, Generating a plurality of driving voltages corresponding to respective temperatures and for driving the light sources; A second step of measuring the temperature; And Selecting a driving voltage corresponding to the measured temperature and supplying the driving voltage to the light source; The driving voltage of the light source is higher as the temperature is lower, the driving method of the liquid crystal display device. The method of claim 7, wherein The light source is, A red light emitting diode emitting red light; A green light emitting diode emitting green light; A blue light emitting diode emitting blue light, In the third step, the driving voltage of the red light emitting diode, the driving voltage of the green light emitting diode, and the driving voltage of the blue light emitting diode corresponding to a temperature are supplied to the red light emitting diode, the green light emitting diode, and the blue light emitting diode, respectively. A method of driving a liquid crystal display device. The method of claim 7, wherein The light source is, A red light emitting diode emitting red light; A green light emitting diode emitting green light; A blue light emitting diode emitting blue light, In the third step, the driving voltage of the red light emitting diode corresponding to a temperature is supplied to the red light emitting diode, and the green light emitting diode and the blue light emitting diode are supplied with a constant voltage, respectively. Way.

Images