KR101888394B1 - Display device and driving method thereof - Google Patents

Abstract

Disclosed is a display device capable of maintaining a fast response speed and reducing power consumption.
The display device of the present invention includes a plurality of pixels defined by intersecting a plurality of gate lines and data lines, each pixel including a pixel display portion including a cholesteric liquid crystal capacitor, and a pixel portion including a cholesteric liquid crystal capacitor And the common voltage supply unit supplies a first common voltage of the AC type having a polarity opposite to that of the image data supplied to the pixels in the homeotropic phase of the black image .

Description

DISPLAY DEVICE AND DRIVING METHOD THEREOF [0002]

BACKGROUND OF THE INVENTION 1. Field of the Invention [0002] The present invention relates to a display device, and more particularly, to a display device and a driving method that can maintain a fast response speed and reduce power consumption.

2. Description of the Related Art Recently, an organic light emitting diode (OLED) display device has been introduced with a liquid crystal display (LCD) as a video display device. LCD displays images by using electrical and optical properties of liquid crystals having anisotropy such as refractive index and permittivity. Each pixel controls the light transmittance of a polarizer through variable polarizations of liquid crystal alignment do. The OLED display is a self-luminous element that emits an organic light-emitting layer by recombination of electrons and holes, has advantages of high luminance, low driving voltage, and ultra thin film. The OLED display implements the gradation by adjusting the magnitude of the current supplied to the OLED pixel according to the data signal by the driving circuit of each pixel.

The image display device has been improved in color reproduction while developing in the direction of high resolution and high definition.

A general liquid crystal display device includes a liquid crystal display panel and a backlight unit for providing light.

In the liquid crystal display panel, a liquid crystal is interposed between two substrates, and the liquid crystal generally has a property of resembling a crystal with different optical properties depending on the direction,

The molecular structure of the liquid crystal is elongated and elongated, and has a characteristic that the arrangement direction thereof is changed by an electric field, a magnetic field, heat, etc. from the outside, or the movement of the molecules is disturbed. This property can easily change the optical properties.

The type of the liquid crystal may be classified into nematic and cholesteric depending on the molecular arrangement. The nematic liquid crystal has no order in the molecular position but has an order oriented toward the molecular axis. Since the directions of the molecules are almost equal to each other in the up and down directions, the polarization is canceled and does not generally exhibit ferroelectricity. The cholesteric liquid crystals have a layered structure and the molecular arrangement in each layer is similar except for the nectic state. Each molecular layer is very thin, the molecular arrangement in the layer is in the major axis direction and the plane of the layer is parallel. The major axis direction of the molecules in each layer is slightly shifted from the major axis direction of the adjacent layer molecules, and the spiral structure as a whole is formed.

A typical cholesteric liquid crystal displays a black image by being arranged in a homeotropic state when a voltage charged in a liquid crystal capacitor of a pixel is at a maximum, and when a voltage charged in the liquid crystal capacitor is minimum, a planar ) State to display color, and scatter light of the liquid crystal in a focal conic state when having the intermediate potential between the homeotropic state and the planar state.

In order to utilize the high potential difference between the pixel voltage and the common voltage in the black implementation of the homeotropic state, a liquid crystal display device including such a cholesteric liquid crystal must supply a high-voltage pixel voltage based on the common voltage of the DC voltage do.

That is, a general liquid crystal display device has a disadvantage in that the pixel voltage of a high voltage is supplied in order to implement the homeotropic state in contrast to the planar state and the focal conic state, thereby consuming a large amount of power.

An object of the present invention is to provide a display device and a driving method capable of reducing power consumption while maintaining a fast response speed.

According to an embodiment of the present invention,

A plurality of pixels defining a plurality of gate lines and a plurality of data lines crossing each other, each pixel including a pixel display unit including a cholesteric liquid crystal capacitor, and a common voltage to the cholesteric liquid crystal capacitor of each pixel Wherein the common voltage supply unit supplies a first common voltage of an AC type having a polarity opposite to that of the image data supplied to each pixel at the time of homeotropic image formation of the black image, Thereby lowering the voltage level of the video data by the level of the first common voltage.

According to another aspect of the present invention, there is provided a method of driving a display device,

A plurality of pixels defining a plurality of gate lines and a plurality of data lines crossing each other, each pixel including a pixel display unit including a cholesteric liquid crystal capacitor, and a common voltage to the cholesteric liquid crystal capacitor of each pixel And supplying a common voltage supply unit to the pixels, the method comprising: supplying image data to the pixels; and analyzing the image data to supply the pixels with a homeotropic image of a black image, And supplying a first common voltage of the AC type having a polarity opposite to that of the video data to the first common voltage and lowering the voltage level of the video data by the level of the first common voltage.

A display device according to an exemplary embodiment of the present invention analyzes a focal conic phase of a home image or a white image of a black image using a polarity control signal and image data to generate a homeotropic ), The common voltage of the AC type is supplied at the time of implementation, and the DC voltage is supplied at the time of the implementation of the focal conic, thereby maintaining the response speed of the general display device and reducing the power consumption I have.

The display device according to another embodiment of the present invention analyzes the focal conic phase of the homeotropic image or the white image of the black image using the polarity control signal and the image data to generate homeotropic ) And a common voltage of an alternating current type at a voltage level lower than the common voltage of the alternating current type at the time of implementing the homeotropic phase in a focal conic phase implementation, So that the response speed of a general display device can be maintained and power consumption can be reduced.

1 is a block diagram schematically showing a display device according to an embodiment of the present invention.
FIGS. 2 to 4 are diagrams showing a state change of the cholesteric liquid crystal according to the intensity of an electric field. FIG.
5 is a block diagram showing a detailed configuration of a common voltage supply unit according to an embodiment of the present invention.
6 is a waveform diagram showing a method of driving a pixel according to an embodiment of the present invention.
7 is a waveform diagram illustrating a method of driving a pixel according to another embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the accompanying drawings, embodiments of the present invention will be described in detail.

One embodiment of the present invention is intended to enable a person skilled in the art to fully understand the technical idea of the present invention. Therefore, the present invention is not limited to the embodiments described below, and other embodiments can be added on the basis of the technical idea of the present invention.

FIG. 1 is a block diagram schematically showing a display device according to one embodiment of the present invention, and FIGS. 2 to 4 are diagrams showing a state change of a cholesteric liquid crystal according to an electric field intensity.

1 to 4, a display device according to an embodiment of the present invention includes an image display unit 110 for displaying an image through pixels, A gate driver 120 for supplying a gate driving signal to the gate line GL of the image display unit 110 and a gate driver 120 for supplying a gate driving signal to the data driver 130 and the gate driver 120 And a common voltage supplier 140 for supplying a common voltage Vcom to the common voltage line VL to supply the common voltage of the pixel.

The image display unit 110 defines pixels by intersecting a plurality of data lines DL and a plurality of gate lines GL and each pixel is defined by intersections of the data lines DL and the gate lines GL A cholesteric liquid crystal capacitor CLC connected to the switching device TR and a storage capacitor CST connected to the cholesteric liquid crystal capacitor CLC.

When the voltage charged in the cholesteric liquid crystal capacitor (CLC) is at a maximum, a black image is displayed by a cholesteric liquid crystal arranged in a homeotropic state, and if the charged voltage is at least a planar ) State by the cholesteric liquid crystals arranged in the state. The storage capacitor (CST) holds the voltage charged in the cholesteric liquid crystal capacitor (CLC) for one frame. In general, the color seen depends on the wavelength of the reflected light, which depends on the pitch of the cholesteric liquid crystals.

When the electric field E applied to the cholesteric liquid crystal is increased to the first electric field Ec or more, the cholesteric liquid crystal is arranged in a homeotropic state. Referring to FIG. 1B, in the homeotropic state, when the electric field E of the cholesteric liquid crystal is sharply reduced to a second electric field Ef or less, the cholesteric liquid crystal is arranged in a planar state. 1C, when the electric field E of the cholesteric liquid crystal in the homeotropic state is made larger than the first electric field Ec and smaller than the second electric field Ef, the cholesteric liquid crystal is focal conic. The liquid crystal in the planar state reflects light of a specific wavelength, and the liquid crystal in the focal-conic state scatters light.

The image display unit 110 including the cholesteric liquid crystal of the present invention can be driven in the inversion mode in which the image data input to the pixel electrodes is inverted for each frame.

The timing controller 150 outputs the polarity control signal POL and the video data Data R, G and B to the data driver 130 and the common voltage supplier 140. The timing controller 150 controls the driving timing of the data driver 130 using a dot clock CLK, a data enable signal DE, a horizontal synchronizing signal Hsync, and a vertical synchronizing signal Vsync And a gate control signal (GCS) for controlling the driving timing of the gate driver 120 are generated and output.

In response to the data control signal from the timing controller 150, the data driver 130 converts the digital image data from the timing controller 150 into an analog data signal (current or voltage signal) using a gamma voltage, And supplies it to the data line DL of the display unit 110.

The gate driver 120 sequentially drives the gate line GL of the image display unit 110 in response to the gate control signal GCS of the timing controller 150. [

The common voltage supply unit 140 supplies the common voltage Vcom supplied to each pixel using the polarity control signal POL and the image data Data R, G and B from the timing controller 150.

The common voltage supplier 140 supplies a common voltage Vcom having a polarity opposite to the polarity of the video data in a homeotropic black image requiring a high voltage. That is, the common voltage Vcom may be an AC signal which is opposite to the image data in a homeotropic black image.

Also, the common voltage supplier 140 of the present invention supplies a DC common voltage Vcom to a white image in a focal conic state.

Therefore, the common voltage supply unit 140 of the present invention receives the polarity control signal POL and the image data Data R, G, and B to generate a homeotropic image or a focal conic image Accordingly, the common voltage Vcom can be selectively converted into alternating current and direct current to maintain a fast response speed and to reduce power consumption.

The detailed configuration of the common voltage supply unit 140 of the present invention will be described in detail with reference to FIG.

FIG. 5 is a block diagram illustrating a detailed configuration of a common voltage supply unit according to an exemplary embodiment of the present invention, and FIG. 6 is a waveform diagram illustrating a method of driving a pixel according to an exemplary embodiment of the present invention.

5 and 6, the common voltage supplier 140 according to an exemplary embodiment of the present invention includes a polarity control signal POL input from a timing controller 150 (FIG. 1) and video data (Data R, G, B), a first common voltage generator 143 for generating an AC common voltage, and a second common voltage generator 143 for generating a DC common voltage A second common voltage generating unit 145 for generating a first common voltage and a second common voltage generating unit 143 for selectively outputting the first common voltage and the second common voltage according to a control signal from the data analyzer 141, 147).

The data analyzer 141 analyzes whether the image data (Data R, G, B) is on the homeotropic (H) or white (F) And controls the selection unit 147 according to the result.

For example, the image data (Data R, G, and B) may be a pulse-shaped signal that can determine whether the image is a black or white image.

That is, the image data (Data R, G, and B) may be supplied with a pulse signal having a high signal and a low signal, and the high signal period may be supplied with a homeotropic (H) , And the low signal interval can be defined as a focal conic (F) of a white image. The setting of the focal conic of the homeotropic (H) image and the white image according to the high signal and the low signal may be changed as much as possible.

The data analyzer 141 generates a common voltage of the AC type when the input image data Data R, G, and B are high signals that can be defined as homeotropic (H) The common voltage from the first common voltage generator 143 is selected.

Here, the AC common voltage output from the first common voltage generator 143 has a polarity opposite to the polarity of the black image data. Therefore, a common voltage of negative polarity is supplied during the black data period of positive polarity, and a common voltage of positive polarity is supplied during the negative polarity of the black data period, resulting in homeotropic (H) The driving voltage at the time of implementation of the H (homeotropic) phase can be reduced by the voltage level of the common voltage so that the power consumption of the entire display device can be reduced.

For example, when the potential difference between the pixel voltage and the common voltage is ± 18 V when implementing a homeotropic image for implementing a black image, a common voltage of ± 5 V is supplied in a polarity different from the pixel voltage, By supplying the pixel voltage of 13V, it is possible to reduce the power consumption by the voltage level of the common voltage.

The data analyzer 141 may be configured to generate a DC voltage having a positive polarity when the input image data Data R, G, and B are low signals that can be defined as a focal conic of a white image, And controls the selector 147 so that the common voltage from the second common voltage generator 145 is selected.

For example, in a focal conic (F) conic mode for realizing a general white image, the potential difference between the pixel voltage and the common voltage is ± 7 V, A common voltage of a direct current type is supplied.

Therefore, the display device according to an embodiment of the present invention can display the homeotropic or white image of the black image using the polarity control signal POL and the image data Data R, G, (F) conical phase to provide a common voltage in the form of an alternating current at the time of implementation of homeotropic (H) phase, and a common voltage in the form of a direct current at the time of implementation of a focal conic So that the response speed of a general display device can be maintained and power consumption can be reduced.

7 is a waveform diagram illustrating a method of driving a pixel according to another embodiment of the present invention.

As shown in FIG. 7, the driving method of a pixel according to another embodiment of the present invention is characterized in that a common voltage supplied at the time of implementing a focal conic (F) The method of driving the pixel according to the embodiment is the same as that of the driving method of the pixel according to the embodiment, and a detailed description thereof will be omitted.

The image data input in the homeotropic (H) phase of the black image according to another embodiment of the present invention is supplied with a pixel voltage of high voltage.

The pixel voltage may have opposite polarity for each frame by the inversion driving method.

For example, when the potential difference between the pixel voltage and the common voltage is ± 18 V at the time of implementing a homeotropic image for implementing a black image, a common voltage of ± 5 V is supplied in a polarity different from the pixel voltage, The pixel voltage of ± 13 V is supplied to the pixel electrode, so that the power consumption by the voltage level (± 5 V) of the common voltage can be reduced.

In addition, a pixel voltage of a low voltage is supplied to the image data inputted at the time of implementing a focal conic (F) conic to realize a white image.

The pixel voltage may have opposite polarity for each frame by the inversion driving method.

For example, in the case of a focal conic (F: focal conic) implementation for realizing a white image, when the potential difference between the pixel voltage and the common voltage is ± 7 V, a common voltage of ± 3 V is supplied in a polarity different from the pixel voltage, The pixel voltage of ± 4 V is supplied to the pixel electrode, so that the power consumption by the voltage level (± 3 V) of the common voltage can be reduced.

Accordingly, the display apparatus according to another embodiment of the present invention analyzes the homeotropic (H) or white (F) image of a black image using a polarity control signal and image data A common voltage of an alternating current type is supplied at the time of implementing a homeotropic phase, and a common voltage of an alternating current type at the time of implementation of the homeotropic phase is provided at the time of implementing a focal conic (F) The common voltage of the AC type having the voltage level lower than the common voltage is supplied to maintain the response speed of the general display device and to reduce the power consumption.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention. Therefore, the technical scope of the present invention should not be limited to the contents described in the detailed description of the specification, but should be defined by the claims.

140: Common voltage supply unit 141: Data analysis unit
143: first common voltage generator 145: second common voltage generator
147:

Claims (10)

A pixel display unit including a plurality of pixels defining a plurality of gate lines and data lines crossing each other, each pixel including a Cholesteric liquid crystal capacitor; And
And a common voltage supply unit for supplying a common voltage to the cholesteric liquid crystal capacitors of the pixels,
Wherein the common voltage supply unit supplies a first common voltage of the AC type having a polarity opposite to that of the image data supplied to each pixel at the time of homeotropic image of the black image, Thereby lowering the voltage level of the video data. The method according to claim 1,
Wherein the common voltage supply unit supplies a DC common second voltage to the pixel in a focal conic state of a white image. The method according to claim 1,
Wherein the common voltage supply unit supplies a third common voltage of the AC type having a voltage level lower than the first common voltage of the AC type to the pixel in the focal conic state of the white image. The method according to claim 1,
Wherein the common voltage supply unit includes:
A data analyzer for analyzing a homeotropic or focal-conic fashion using the polarity control signal supplied from the timing controller and the image data;
A first common voltage generator for generating the first common voltage of the AC type;
A second common voltage generator for generating a second common voltage in the form of a direct current or a third common voltage having an alternating voltage of a voltage level lower than the first common voltage; And
And a selection section for selecting any one of the first and second common voltage generation sections by a control signal of the data analysis section. The method according to claim 1,
Wherein the image data is a pulse signal capable of discriminating whether the image data is a black image or a white image. A plurality of pixels defining a plurality of gate lines and a plurality of data lines crossing each other, each pixel including a pixel display unit including a cholesteric liquid crystal capacitor, and a common voltage to the cholesteric liquid crystal capacitor of each pixel A method of driving a display apparatus having a common voltage supply unit,
Supplying image data to each pixel; And
Analyzing the image data to supply a first common voltage of an AC type having a polarity opposite to that of the image data supplied to each pixel at the time of homeotropic image of the black image, And lowering the voltage level of the image data by a predetermined amount. The method according to claim 6,
Further comprising the step of analyzing the image data to supply a DC common second voltage to the pixel at the time of implementation of a focal conic of a white image. The method according to claim 6,
And analyzing the image data to supply a third common voltage of the AC type having a voltage level lower than the first common voltage of the AC type to the pixel at the time of implementing the focal conic of the white image And a driving method of the display device. The method according to claim 6,
Wherein the step of supplying the common voltage comprises:
Analyzing a homeotropic or focal-conic fashion using a polarity control signal supplied from a timing controller through a data analysis unit and the image data;
Generating a first common voltage of the AC type through a first common voltage generator;
Generating a third common voltage of the AC type having a voltage level lower than the second common voltage of the DC type or the first common voltage of the AC type through the second common voltage generator; And
And selecting one of the first and second common voltage generators through the selection unit. The method according to claim 6,
Wherein the image data is a pulse signal capable of discriminating whether the image data is a black image or a white image.

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