KR100637438B1 - Liquid crystal display - Google Patents

Abstract

The present invention relates to a liquid crystal display device. According to the present invention, the current flowing through each of the light emitting diodes R, G, and B for each luminance is equally controlled. In this way, the LCD panel can maintain a uniform luminance even when the characteristics of the light emitting diode are changed to change the voltage at which the light emitting diodes are turned on.

LCD, LED, Current Control

Description

Liquid crystal display

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

The present invention relates to a liquid crystal display device, and more particularly to a liquid crystal display device of the field sequential driving method.

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, flat displays such as liquid crystal displays (LCDs) instead of cathode ray tubes (CRTs) are required. 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). It is a ticket market value which acquires 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 illustrated 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, and a drain electrode and a common voltage Vcom of the TFT. 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. In this case, 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 consisting 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. To display the desired color.

As described above, in a liquid crystal display device that displays color using a single light source and a three-color color filter layer, since each unit pixel is required for each of the R, G, and B regions, three times as many pixels are used as for a black and white display. 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 periodically turns on independent light sources of R, G, and B colors, and applies a color signal corresponding to each pixel in synchronism 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.

An example of such a field sequential driving method is an analog 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 T1 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 T2 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 T3 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 T1, T2, and T3 sections, respectively.

Referring to FIG. 2, the period in which the R color is actually displayed is a period Tr from the time t2 to t3 when the R backlight is emitted, and the G color is displayed in the period from the time t5 to t6 when the G backlight is emitted ( Tg), and the color B is displayed in the period Tb from the time t8 to t9 when the B backlight emits light.

On the other hand, as described above, in the field sequential driving method, an independent light source of each of R, G, and B colors is used to display colors of R, G, and B, and as such a light source, a light-emitting diode, Hereinafter referred to as LED). Therefore, the characteristics of the LED serves as an important factor in determining the characteristics of the color, gray scale, brightness, etc. of the LCD panel.

Conventionally, the voltage supplied to each of the LEDs of R, G, and B is varied to control the current flowing through the LEDs for each luminance. However, color LEDs except for white LEDs usually have characteristics of varying characteristics of LEDs according to time, temperature, and voltage. As a result, when the voltage input to the LEDs is changed, the characteristics of the LEDs are changed so that each LED is turned on ( Vf) may change, which causes a problem in that luminance of the LCD panel is uneven.

SUMMARY OF THE INVENTION The present invention has been made in an effort to provide a field-sequential driving liquid crystal display device in which each of R, G, and B maintains uniform luminance.

A liquid crystal display device according to an aspect of the present invention for achieving the above object is defined by a plurality of data lines for transmitting a data voltage representing an image, a plurality of scan lines for transmitting a scan signal, the data line and the scanning line A liquid crystal display panel including a plurality of pixels, a scan driver for sequentially supplying a scan signal to the scan line, a data driver for supplying a gray voltage corresponding to grayscale data to the data line, light of a first color to each pixel, First, second and third light emitting diodes sequentially outputting light of a second color and light of a third color, a light source controller for controlling the lighting timing of the first to third light emitting diodes, and the first light emitting diode. A first resistor coupled between the cathode of the light source controller and the light source controller, between the cathode of the second light emitting diode and the light source controller Control the second resistor, and comprising a third resistor connected between the cathode and the light source control of the third light-emitting diode,

The light source controller adjusts voltages applied to the first to third resistors so that currents flowing through the first to third light emitting diodes are the same.

A liquid crystal display according to another aspect of the present invention includes a plurality of data lines for transmitting a data voltage representing an image, a plurality of scan lines for transmitting a scan signal, the data lines, and a plurality of pixels defined by the scan lines. A liquid crystal display panel, a scan driver for sequentially supplying scan signals to the scan lines, a data driver for supplying gray voltages corresponding to grayscale data to the data lines, and red and green light for each pixel, respectively. The first, second and third light emitting diodes sequentially outputting the light of the light and blue (BLUE), and the first to third resistors having one end connected to the cathode of the first to third light emitting diodes, respectively. And controlling the lighting timing of the first to third light emitting diodes, and the currents flowing through the first to third light emitting diodes are the same. And a light source controller that adjusts a voltage applied to the third resistor.

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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.

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

As shown in FIG. 3, the liquid crystal display according to the exemplary embodiment of the present invention includes a liquid crystal display panel 100 (hereinafter, referred to as an “LCD panel”), a scan driver 200, a data driver 300, and a gray voltage. The generator 500 includes a timing controller 400, light emitting diodes 600a, 600b, and 600c that output R, G, and B light sources, respectively, and a light source controller 700.

The LCD panel 100 includes a plurality of scan lines (not shown) for transmitting a gate-on signal. The LCD panel 100 is insulated from and intersects with the plurality of scan lines and transfers gray data voltages and reset voltages corresponding to gray data. Data lines (not shown) are formed. A plurality of pixels arranged in a matrix form is surrounded by a scan line and a data line, and each pixel includes a thin film transistor (not shown) and a drain electrode of the thin film transistor, in which a gate electrode and a source electrode are connected to the scan line and the data line, respectively. A pixel capacitor (not shown) and a storage capacitor (not shown) are connected to each other.

The scan 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.

The light emitting diodes 600a, 600b, and 600c respectively output light corresponding to R, G, and B to the LCD panel, and the light source controller 700 controls when the light emitting diodes 600a, 600b, and 600c are turned on. In this case, according to an exemplary embodiment of the present invention, the timing controller 500 may be configured to supply the grayscale data from the data driver 300 to the data line and to turn on the R, G, and B light emitting diodes by the light source controller 700. It can be synchronized by the control signal provided by.

In addition, the light source controller 700 according to the embodiment of the present invention allows the same current to flow through each of the light emitting diodes 600a, 600b, and 600c.

In detail, a resistor (not shown) is connected to the cathode of each of the light emitting diodes 600a, 600b, and 600c, and the light source controller 700 senses a voltage applied to the resistor. That is, a resistor may be connected inside the light source controller 700 or may be connected between the light source controller 700 and the light emitting diodes 600a, 600b, and 600c, respectively, and the light source controller 700 may sense a voltage applied to each resistor. By controlling this, the predetermined constant current flows for each luminance through the resistor.

In general, light emitting diodes have characteristics that vary with time, temperature, and voltage, but are relatively insensitive to changes in current. Therefore, as shown in the embodiment of the present invention, when the same current is controlled to flow through each of the light emitting diodes 600a, 600b, and 600c, the characteristics of the light emitting diodes 600a, 600b, and 600c vary according to time, temperature, and voltage changes. Even when the voltage Vf at which the light emitting diodes 600a, 600b and 600c are turned on changes in the luminance characteristics of the light emitting diodes 600a, 600b and 600c, the luminance is uniformly displayed on the LCD panel 100. Can be.

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 LCD panel is uniform even when the voltage of the light emitting diode is changed by changing the characteristics of the light emitting diode by controlling the current flowing through each of the light emitting diodes R, G, and B according to luminance. One brightness can be maintained.

Claims (3)

A liquid crystal display panel comprising a plurality of data lines for transmitting a data voltage representing an image, a plurality of scanning lines for transmitting a scanning signal, a plurality of pixels defined by the data lines and the scanning lines, A scan driver for sequentially supplying scan signals to the scan lines; A data driver for supplying a gray voltage corresponding to gray data to the data line; First, second, and third light emitting diodes sequentially outputting light of a first color, light of a second color, and light of a third color to each pixel, A light source controller controlling a lighting timing of the first to third light emitting diodes; A first resistor connected between the cathode of the first light emitting diode and the light source controller, A second resistor connected between the cathode of the second light emitting diode and the light source controller, and A third resistor connected between the cathode of the third light emitting diode and the light source controller Including; And the light source controller adjusts voltages applied to the first to third resistors so that currents flowing through the first to third light emitting diodes are the same. The method of claim 1, The first color, the second color, and the third color are red, green, and blue, respectively. A liquid crystal display panel comprising a plurality of data lines for transmitting a data voltage representing an image, a plurality of scanning lines for transmitting a scanning signal, a plurality of pixels defined by the data lines and the scanning lines, A scan driver for sequentially supplying scan signals to the scan lines; A data driver for supplying a gray voltage corresponding to gray data to the data line; First, second and third light emitting diodes sequentially outputting red light, green light, and blue light to each pixel, and A first to third resistors having one end connected to the cathodes of the first to third light emitting diodes, respectively, controlling the lighting timing of the first to third light emitting diodes, and the first to third light emitting diodes. A light source controller that adjusts voltages applied to the first to third resistors so that the current flowing through them is the same Liquid crystal display comprising a.

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