KR100590059B1 - Liquid crystal display device and 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, it is determined whether the backlight is on or off, and when the backlight is on, the grayscale data voltage corresponding to the grayscale data is applied to the data line. When the backlight is off, only one voltage corresponding to 1 bit is generated. Apply to data line.

As a result, power consumption for processing grayscale data can be reduced.

Power Consumption, Liquid Crystal Display, Backlight

Description

Liquid crystal display and its driving method {LIQUID CRYSTAL DISPLAY DEVICE AND 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 diagram illustrating a liquid crystal display according to an exemplary embodiment of the present invention.

5 is a diagram illustrating in detail a gray voltage generator according to an exemplary embodiment of the present 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 and a driving method thereof for reducing power consumption.

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. In FIG. 2, the driving voltage refers to a voltage applied to the liquid crystal and the optical tranmittance refers to a transmission ratio with respect to the applied light when light is applied to the liquid crystal. That is, the light transmittance refers to the degree of twist that the liquid crystal can transmit light.

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 light transmittance of the liquid crystal.

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 light transmittance of the liquid crystal is determined according to the applied gradation waveform to perform gradation display.

In the conventional liquid crystal display, the backlight is turned on and the R, G, and B gray data are applied to the data line to display the gray scale. At this time, when the bits of each gray level are n bits for the R, G, and B gray levels, 3 * n bits of data are processed and applied to the data line. In addition, even when the backlight is turned off, the data processing is performed for all of the R, G, and B gray levels in the same way. When the backlight is turned off, the R, G, and B grayscale data need not be applied to the data line. Processing the R, G, and B grayscale data causes a problem of increasing power consumption.

SUMMARY OF THE INVENTION The present invention has been made in an effort to solve the above-described problems of the related art, and to provide a liquid crystal display and a driving method thereof to reduce power consumption when the backlight is turned off.

A liquid crystal display device according to a feature of the present invention for achieving the above object is

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 light source for outputting red, green, and blue light to the pixel;

A gray voltage generator for generating a gray voltage corresponding to grayscale data when the backlight is on in response to on / off information of the light source, and generating only a voltage corresponding to 1 bit when the backlight is off;

 And a data driver for supplying a voltage output from the gray voltage generator to a corresponding data line. The gray voltage generator may include a plurality of switches configured to output gray data voltages corresponding to the gray data; And when the backlight is on, controls the plurality of switches to output gradation data voltages, and when the backlight is off, controls only one switch of the plurality of switches to supply an arbitrary voltage corresponding to the 1 bit. And a switch controller for controlling the output.

A method of driving a liquid crystal display according to another feature of the present invention is

In the driving method of a liquid crystal display device comprising a liquid crystal formed between the first and second substrates, and transmits red, green, blue light to the pixel,

(a) detecting whether the backlight for outputting light is on or off;

(b) generating an arbitrary voltage corresponding to one bit when the backlight is detected to be off in step (a);

(c) applying an arbitrary voltage corresponding to the one bit of step (b) to the data line.

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.

Hereinafter, a liquid crystal display and a driving method thereof according to an exemplary embodiment of the present invention will be described in detail with reference to FIGS. 4 and 5.

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

As shown in FIG. 4, 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. And light emitting diodes 600a, 600b, and 600c respectively outputting R, G, and B light sources, and a light source controller 700.

 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 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. Here, the timing controller 400 according to the embodiment of the present invention corresponds to not only the gray scale data R, G, and B data, but also the control signal Sb supplied to the light source controller 700. The ON / OFF information of the 600b and 600c is supplied to the gray voltage generator 500. That is, the timing controller 400 generates ON / OFF information of the light emitting diodes 600a, 600b, and 600c based on the control signal Sb and transmits the generated ON / OFF information to the gray voltage generator 500.

The gray voltage generator 500 generates a gray voltage having a magnitude corresponding to gray data R, G, and B DATA and supplies the gray voltage to the data driver 300. Here, the gray voltage generator 500 according to an embodiment of the present invention uses not only gray data (R, G, B DATA) but also ON / OFF information of the light emitting diodes 600a, 600b, and 600c. When the light emitting diode is ON, a gray voltage corresponding to the gray data R, G, and B DATA is generated and supplied to the data driver 300. When the light emitting diode is OFF, the gray data is generated. Rather than supplying the gray scale voltage corresponding to (R, G, B DATA) to the data driver 300, any one gray voltage (that is, information corresponding to one bit) is supplied to the data driver 300. Specific methods for this will be described in detail below.

That is, since the gray scale does not need to be displayed on the liquid crystal display when the light emitting diode is OFF, the gray voltage generator 500 processes all the gray scale data when the light emitting diode is OFF. The power consumption can be further reduced by processing only one bit of data, which is one gray level voltage, and providing the data driver 300 to the data driver 300 without providing 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 the embodiment of the present invention, a light emitting diode is used as the backlight, but the present invention is not limited thereto.

5 is a diagram illustrating in detail a gray voltage generator 500 according to an exemplary embodiment of the present invention.

As shown in FIG. 5, the gray voltage generator 500 according to an exemplary embodiment of the present invention includes an LED detector 520, a switch controller 540, a plurality of resistors R1, R2 .. Rn + 1, Switches S1, S2, .. Sn and amplifiers Amp1, Amp2 .. AmpN. Here, the amplifiers Amp1, Amp2 ... AmpN amplify the output voltages of the corresponding switches S1, S2, S3..Sn and supply them to the data driver 300.

As shown in FIG. 5, a plurality of resistors R1, R2, ..Rn + 1 are connected in series between the voltage source VDD and ground, and each switch S1, S2, .. Sn is connected to the plurality of resistors. Is connected between a plurality of resistors R1, R2 .. Rn + 1 to provide the data driver 300 with a voltage divided by this divided voltage corresponds to a gradation voltage.

The LED detecting unit 520 determines whether the light emitting diodes 600a, 600b, and 600c are turned on / off based on the on / off information of the light emitting diodes transmitted from the timing controller 400. The signal is sensed and supplied to the switch controller 540.

The switch controller 540 uses the input gray level data R, G, and B data and a signal corresponding to on / off of the light emitting diode. Turn on When the switch corresponding to the grayscale data is turned on, the divided voltage according to the resistance connected to the turned on switch is amplified by the amplifier and transmitted to the data driver 300. The voltage amplified and provided to the data driver 300 is a gray data voltage.

Meanwhile, when the light emitting diode is ON, the switch controller 540 controls the on / off of the plurality of switches in the same manner as described above with respect to all grayscale data R, G, and B data, and thus the data driver 300. To the gray level voltage. Therefore, in this case, since the switch controller 540 has to process all gray data (R, G, DATA), a lot of power is consumed.

Herein, when the switch controller 540 receives a signal indicating that the LED is off from the LED sensing unit 520, the switch controller 540 turns on any of the switches S1 to Sn to turn on any of the corresponding voltages (that is, 1 bit). Corresponding to the information of S1) is supplied to the data driver 300. In this way, only the arbitrary switch is turned on and the corresponding voltage is supplied to the data driver 300 while the signal from the LED sensor 530 indicates that the light emitting diode is turned off. Therefore, the switch control unit 540 processes only one switch by processing the off signal of the light emitting diode without controlling all the switches corresponding to the grayscale data R, G, and B DATA, thereby further reducing power consumption. Will be. In addition, when the light emitting diode is off, only one arbitrary switch is continuously turned on, so that switching loss can be further reduced. When the light emitting diode is turned off, the switch controller 540 turns on any one switch and supplies a voltage corresponding thereto to the data driver 300. However, the switch controller 540 does not provide any voltage corresponding to the switch. A voltage other than the voltage corresponding to the switch may be supplied to the data driver 300.

In the above description, only the analog type liquid crystal display device is described, but when the light emitting diode is turned off, the power consumption can be reduced by applying one arbitrary gray scale waveform to the digital liquid crystal display device. In the above, the field sequential liquid crystal display device is described as an embodiment, but the present invention is not limited thereto, and the present invention can be applied to a liquid crystal display device having a general color filter method.

Although the preferred 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.

As described above, according to the present invention, when the backlight is off, power consumption may be further reduced by processing only information corresponding to 1 bit and applying the information to the liquid crystal display.

Claims (9)

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 light source for outputting red, green, and blue light to the pixel; A gray voltage generator for generating a gray voltage corresponding to grayscale data when the backlight is on in response to on / off information of the light source, and generating only a voltage corresponding to 1 bit when the backlight is off;  And a data driver for supplying a voltage output from the gray voltage generator to a corresponding data line. The method of claim 1, And a timing controller configured to receive a plurality of clocks to generate a control signal for controlling the gate driver, the data driver, and the light source, and to generate the light source on / off information using the control signal. The method according to claim 1 or 2, And the voltage corresponding to the one bit is one of the gray voltages corresponding to the gray data. The method of claim 2, The gray voltage generator A plurality of switches configured to output gray data voltages corresponding to the gray data; An LED sensing unit receiving on / off information of the light source from the timing controller and transmitting on / off information of the backlight; And When the on information of the backlight is transmitted from the LED sensing unit, the plurality of switches are controlled to output gray level data voltages. When the off information of the backlight is transmitted from the LED sensing unit, the plurality of switches are controlled. And a switch controller for controlling only one of the switches to be turned on and the other switches to be turned off to output an arbitrary voltage corresponding to the one bit.  The method according to claim 1 or 2, And when the backlight is off, continuously applying only a voltage corresponding to the first bit to the data line. In the driving method of a liquid crystal display device comprising a liquid crystal formed between the first and second substrates, and transmits red, green, blue light to the pixel, (a) detecting whether the backlight for outputting light is on or off; (b) generating an arbitrary voltage corresponding to one bit when the backlight is detected to be off in step (a); and (c) applying an arbitrary voltage corresponding to the one bit of step (b) to a data line. The method of claim 6, And continuously applying a voltage corresponding to the one bit to the data line when the backlight is off. The method of claim 6, And generating a gray data voltage corresponding to the gray data which is input when the backlight is detected to be on in the step (a) and applying the gray data voltage to the data line. The method according to any one of claims 6 to 8, And wherein the arbitrary voltage is any one of a plurality of gradation data voltages corresponding to the gradation data.

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