KR100982065B1 - Liquid crystal display and driving method thereof - Google Patents

Abstract

Disclosed are a liquid crystal display and a driving method thereof capable of improving image quality irrespective of image type.

A liquid crystal display device according to the present invention comprises: a liquid crystal panel having a plurality of pixels in which gate lines and data lines are arranged in a matrix, and displaying image data on each pixel; The first and second timing signals for driving the liquid crystal panel are generated by using the synchronization signal detected from the image data, and the image type according to the change of movement between the previous frame image and the current frame image of the image data is determined. A control unit; A gate voltage adjuster for adjusting a different high potential gate voltage according to the determined image type; A gate driver for sequentially supplying the adjusted high potential gate voltage to the liquid crystal panel according to the first timing signal; And a data driver for supplying a gray voltage corresponding to the image data to the liquid crystal panel according to the second timing signal. Therefore, according to the present invention, different high potential gate voltages are applied depending on the type of image determined according to the movement, thereby improving the gate charging characteristic in the moving image.

LCD, Still Image, Moving Image, Gate Voltage Adjustment

Description

Liquid crystal display and driving method             

1 is an equivalent circuit diagram of a unit pixel of a general liquid crystal panel.

FIG. 2 is a voltage waveform diagram applied to a general liquid crystal panel in FIG. 1. FIG.

FIG. 2 is a voltage waveform diagram applied to a general liquid crystal panel in FIG. 1. FIG.

Figure 3 is a waveform diagram of a high potential gate voltage having a lower potential in a later section.

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

5A and 5B illustrate waveforms of gate voltages output from the gate voltage adjuster of FIG. 4.

6 is a view showing a state in which a partial image is selected in the partial image selection unit of FIG.

<Name of the code for the main part of the drawing>

20: control unit 21: timing signal generation unit

22: frame memory 23: partial image selection unit                 

24: motion determination unit 25: image determination unit

26: LUT memory 30: Gate voltage adjuster

40: gate driver 50: data driver

60: liquid crystal panel

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device, and more particularly, to a liquid crystal display device and a driving method thereof capable of improving image quality regardless of image type.

In general, a liquid crystal display device is a display device in which a desired image is displayed by individually supplying data signals according to image information to pixels arranged in a matrix, and adjusting light transmittance of the liquid crystal layer. .

Such a liquid crystal display includes a liquid crystal panel in which pixels are arranged in an active matrix, a gate driver and a data driver for driving the liquid crystal panel.

The liquid crystal panel includes a liquid crystal layer including color filter substrates and thin film transistor array substrates facing each other, and liquid crystals filled in spaced intervals of the color filter substrate and thin film transistor array substrates.

Common electrodes and pixel electrodes are formed on inner surfaces of the color filter substrate and the thin film transistor array substrate, respectively. In this case, when a data signal is applied to the pixel electrode while a predetermined common voltage is applied to the common electrode, an electric field due to a potential difference between the pixel voltage and the common voltage is applied to the liquid crystal layer. Therefore, the light transmittance of the liquid crystal layer may be individually controlled by different data signals applied to the pixel electrode to display a desired image.

Data lines for transmitting the data signal supplied from the data driver to the pixel electrode and the high potential gate voltage supplied from the gate driver are sequentially selected on the thin film transistor array substrate by one line. Gate lines are arranged to cross each other.

A thin film transistor (TFT), which is used as a switching element, is connected to the pixel electrodes, and the TFT is turned on by a high potential gate voltage supplied through the gate lines. As the data signal supplied through the data lines is applied to the pixel electrode through the source electrode and the drain electrode of the TFT, an electric field between the common voltage applied to the common electrode and the data signal applied to the pixel electrode is applied. The light transmittance of the liquid crystal layer is adjusted.

The driving of the liquid crystal display device configured as described above will be described in detail with reference to the accompanying drawings.

1 is an equivalent circuit diagram of a unit pixel of a general liquid crystal panel. FIG. 2 is a voltage waveform diagram applied to a general liquid crystal panel in FIG. 1.

1 and 2, the common voltage Vcom is applied to the common electrode, the voltage Vdata of the data signal is applied to the source electrode of the TFT 100 through the data line 103, and has a high potential gate. The voltage Vgh is applied to the gate electrode of the TFT 100 through the gate line 101 every frame. At this time, the high potential gate voltage (Vgh) is usually applied as a square wave.

Therefore, first, in the turn-on period of the TFT 100 to which the high potential gate voltage Vgh of the nth frame is applied, the voltage Vdata of the positive data signal, that is, the (+) field is generated from the source electrode. The liquid crystal layer 102 is driven by being supplied to the pixel electrode Vp through the drain electrode, and is charged in the liquid crystal capacitors Clc and 104.

The parasitic capacitance Cgs caused by the overlap between the gate electrode and the drain electrode of the TFT 100 is turned on when the gate voltage transitions from the high potential Vgh to the low potential Vgl and the TFT 100 is turned off. 105, the voltage variation of the gate electrode affects the pixel electrode connected to the drain electrode, so that a voltage drop occurs from the charged pixel voltage Vp, which is referred to as a variation ΔVp of the pixel voltage.

The variation ΔVp of the pixel voltage may be expressed by Equation 1 below.

Here, Clc is a liquid crystal capacitor, Cst is a storage capacitor, Cgs is a parasitic capacitance between the gate electrode and the drain electrode, and Vgh and Vgl represent high potential gate voltage and low potential gate voltage, respectively.                         

As shown in Equation 1, due to the parasitic capacitance Cgs between the gate electrode and the drain electrode, variations in the predetermined pixel voltage Vp occur.

Therefore, even when the voltage Vdata of the data signal is applied to the pixel electrode, the voltage actually applied to the liquid crystal layer 102 is reduced by the variation of the pixel voltage Vp from the voltage Vdata of the data signal. ) Will exist.

Meanwhile, in the turn-off period of the TFT 100 transitioning from the high potential gate voltage Vgh to the low potential gate voltage Vgl, the liquid crystal capacitor Clc charged in the liquid crystal layer 102 is sustained at the pixel electrode. Is supplied to maintain the driving of the liquid crystal layer.

On the other hand, in the n + 1 frame, since the inversion driving method described above is applied, the voltage Vdata of the negative data signal is supplied from the source electrode to the pixel electrode through the drain electrode, and the liquid crystal capacitor 104 is applied. ) Will be charged.

Therefore, the pixel voltage Vp of the n + 1th frame is ideally matched with the pixel voltage Vp of the nth frame in the turn-on, transition, and turn-off periods of the TFT 100 based on the common voltage Vcom. The voltage waveform should be symmetrical.

Accordingly, since the pixel voltage Vp is lower than the voltage Vdata of the data signal due to the variation ΔVp of the pixel voltage, as described above, the pixel of the nth frame and the n + 1th frame is actually used. The voltages Vp are not symmetrical with each other as shown in FIG.

As such, the pixel voltage Vp is asymmetrically present for each frame, resulting in luminance deviation, and flicker occurs due to the luminance deviation.

As a method for eliminating the flicker, a method of transferring a predetermined period (adjustment region) after the high potential gate voltage to a lower potential has been proposed.

That is, as shown in FIG. 3, the high potential gate voltage (for example, 25 V) of a square wave is applied, and the high potential gate voltage is transferred to a lower potential (10 V) during the adjustment region after a certain point of time, and then turned. At the off time point, the low potential is shifted from the low potential gate voltage (Vgl, for example, -5V).

Accordingly, the transition to the lower potential (10V) in the adjustment region of the high potential gate voltage, thereby minimizing the effect of the voltage variation of the gate electrode on the pixel electrode connected to the drain electrode due to the parasitic capacitance (Cgs) Flicker due to the variation ΔVp can be removed.

However, this adjustment of the high potential gate voltage is effective to remove flicker only in still images, and in the case of moving images, the flicker does not become a problem because the screen is dynamically changed.

In addition, if the predetermined period of the rear end of the high potential gate voltage is transferred to a lower potential, the lower drop voltage lowers the charging characteristic of the gate line, thereby preventing the accurate image from being displayed.

In general, in the case of a still image, the screen is fixed every frame, so that a person can recognize the flicker. In the case of a moving image, the screen is dynamically changed every frame, so the flicker is caused by the human. It will not be detected.

Thus, flicker may or may not be effective depending on whether the image is a moving image or a still image.

In this case, as described above, if an unadjusted high potential gate voltage is applied irrespective of the type of image, flicker may be removed, but in the case of moving images, the gate charging characteristic may be degraded by the adjusted high potential gate voltage. A problem occurred.

In particular, in the case of high resolution or other application techniques (e.g., data blinking, etc.), it is important to secure more gate charging time. This is clearly a problem.

Accordingly, the present invention has been made to solve the above problems, and provides a liquid crystal display device and a driving method thereof which can improve image quality by applying different high potential gate voltages according to the movement of an image. There is a purpose.

According to an exemplary embodiment of the present invention for achieving the above object, a liquid crystal display device has a plurality of pixels in which the gate lines and the data lines are arranged in a matrix form, the liquid crystal panel for displaying image data in each pixel ; The first and second timing signals for driving the liquid crystal panel are generated by using the synchronization signal detected from the image data, and the image type according to the change of movement between the previous frame image and the current frame image of the image data is determined. A control unit; A gate voltage adjuster for adjusting a different high potential gate voltage according to the determined image type; A gate driver for sequentially supplying the adjusted high potential gate voltage to the liquid crystal panel according to the first timing signal; And a data driver for supplying a gray voltage corresponding to the image data to the liquid crystal panel according to the second timing signal.

According to the liquid crystal display device, the control unit includes: a partial image selecting unit for selecting partial images to determine a change in motion from the previous frame image and the current frame image; A motion determination unit for comparing the partial images of the previous frame image and the partial images of the current frame image to determine whether to move; And an image determination unit for determining an image type of the image data by using a distribution ratio of the partial images determined as the movement, and outputting a different gate control signal accordingly.

According to the liquid crystal display, the gate voltage adjusting unit outputs a high potential gate voltage as it is when the gate control signal is a signal for a moving image, and constants at a rear stage when the gate control signal is a signal for a still image. It can be adjusted to a high potential gate voltage that transitions to a lower potential in the interval.                     

According to another preferred embodiment of the present invention, a method of driving a liquid crystal display device comprises the steps of determining an image type by using a previous frame image and a current frame image of image data, wherein the image type is one of a still image or a moving image. -; Adjusting a high potential gate voltage according to the type of the determined image; Sequentially supplying the adjusted high potential gate voltage to a liquid crystal panel; And supplying a gray voltage for the image data to the liquid crystal panel in synchronization with the high potential gate voltage.

According to the driving method of the liquid crystal display, the image type may be determined based on a change in motion between the partial images respectively selected from the previous frame image and the current frame image.

Hereinafter, with reference to the accompanying drawings will be described an embodiment of the present invention.

4 is a block diagram schematically illustrating a configuration of a liquid crystal display according to an exemplary embodiment of the present invention. 5A and 5B illustrate waveforms of gate voltages output from the gate voltage adjuster of FIG. 4.

Referring to FIG. 4, the liquid crystal display according to the present invention includes a liquid crystal panel 60 having a plurality of pixels arranged in a matrix form along the gate lines GL and the data lines DL, and an external analog image. A change in motion between the digital video card 10 and the previous image data supplied from the digital video card 10 and the current image data while converting the data into digital image data while detecting the synchronization signals Vsync and Hsync. A control unit 20 for determining a type of an image according to the control unit, generating a first timing signal and a second timing signal using the synchronization signal, and a gate voltage for adjusting a high potential gate voltage according to the type of the image. A crab for sequentially supplying the high potential gate voltage adjusted from the gate voltage adjuster to the gate lines GL according to the adjuster 30 and the first timing signal. And a data driver 50 for supplying a gray voltage corresponding to the image data to the data lines DL according to the second timing signal.

The digital video card 10 converts analog image data into digital image data R, G, and B, and detects synchronization signals Vsync and Hsync included in the analog image data. The converted digital image data and the synchronization signals Vsync and Hsync are supplied to the controller 20.

The controller 20 includes a timing signal generator 21, a frame memory 22, a partial image selector 23, a motion determiner 24, an image determiner 25, and a look-up table (LUT) memory. It comprises 26. Here, the image data supplied from the digital video card 10 is supplied to the frame memory 22, and the synchronization signals Vsync and Hsync are supplied to the timing signal generator 21.

The timing signal generator 21 generates a first timing signal to be supplied to the gate driver 40 and a second timing signal to be supplied to the data driver 50 by using the synchronization signals Vsync and Hsync. Output it.

Here, the first timing signal includes a gate shift clock (GSC), a gate start pulse (GSP), a gate output enable (GOE), and the second timing signal includes a source shift clock (SSC) and a source start (SSP). Pulse) and SOE (Source Output Enable) may be included. The first timing signal controls the high potential gate voltage supplied from the gate driver 40 to the gate lines GL of the liquid crystal panel 60, and the second timing signal is controlled by the data driver 50. The gray voltage according to the image data supplied to the data lines DL of the liquid crystal panel 60 is controlled.

The frame memory 22 temporarily stores image data supplied from the digital video card 10, and previous image data and current image data may be stored. That is, the frame memory 22 is provided with a space for storing two image data at a time, one of the two spaces provided in the previous image data is stored in one space, while the current image data is stored in another space Will be. At this time, when the next image data is input, the next image data is stored in place of the previous image data stored in the one space. Further, when the next image data is input, the next image data is stored in place of the current image data stored in the other space. The image data sequentially input in this manner is alternately stored in two spaces allocated to the frame memory 22.

Alternatively, a plurality of storage spaces may be provided in the frame memory 22, and image data supplied from the digital video card 10 may be stored in the plurality of storage spaces. In this case, when a plurality of image data is previously stored in the plurality of storage spaces, the input image data may be stored in a storage space that is stored first in time among the plurality of storage spaces.                     

At this time, the previous image data and the current image data stored in the frame memory 22 are supplied to the partial image selecting unit 23 together.

The partial image selecting unit 23 selects a predetermined number of partial images for determining a change in motion from the previous image data and the current image data. That is, partial images are selected from both the previous image data and the current image data. Here, each of the partial images preferably includes at least one pixel value, that is, grayscale data. That is, the partial image may be selected to have a size of 2 pixels * 2 pixels or 3 pixels * 3 pixels. Each pixel included in the partial image includes a corresponding pixel value. At this time, it is preferable to optimize the number of selected partial images. That is, if too many partial images are selected, the time required for judging a change in motion is too long for the selected partial images, whereas if too few partial images are selected, the selected partial images are thus selected. In case of judging the motion through the change of motion, the decision error is more likely to occur. Accordingly, the size of the sum of the selected partial images may be selected to occupy an area of 30 to 60% of one image data of the previous image data or the current image data.

In addition, the number of partial images selected from each of the previous image data and the current image data is the same and preferably selected to correspond to the same position. That is, the number of partial images selected from the previous image data and the number of partial images selected from the current image data must match. Further, each of the partial images selected from the previous image data and each of the partial images selected from the current image data must correspond to each other at the same position.

The partial image selecting unit 23 may randomly select partial images or select partial images based on a preset number of partial images, a size of a partial image, and a reference position. For example, as shown in Fig. 6, when all 64 pixels P1 to P64 exist in one image data, the number of partial images is four, and the size of the partial images is 2 pixels * 2 pixels, If the reference position is set to P10, P13, P34, and P37, the first partial image including P10, P11, P18, and P19 from the image data, the second partial image including P13, P14, P21, and P22; The third partial image including, P34, P35, P42, and P43 and the fourth partial image including P37, P38, P45, and P46 may be selected as partial images for motion determination.

The motion determination unit 24 compares the pixel values of the partial images of the previous image data selected by the partial image selection unit 23 and the partial images of the current image data to determine whether the motion is performed.

For example, when the size of the partial image is 2 pixels * 2 pixels, four pixels exist, and the pixel values of the previous image data corresponding to the positions of the four pixels are compared with the pixel values of the current image data. It is determined whether or not both pixel values are changed. In this case, when a variation occurs in any one of the four pixels, it may be determined that there is motion in the corresponding partial image.

In this way, it is determined whether there is motion for each partial image, and the determined result is supplied to the image determination unit 25.

The image determining unit 25 determines whether the image data is a still image or a moving image, that is, the type of the image based on a determination result of whether the movement is supplied from the motion determining unit 24, and according to the determined result. The gate control signals FLK and FLK 'are supplied to the gate voltage adjuster 30. In this case, a look-up table included in the LUT memory 26 may be used to determine the type of the image. In the lookup table, an image type according to a ratio of partial images determined to have movement among all selected partial images may be preset and stored.

For example, if the ratio of the partial images determined to have a motion among the entire partial images is set to 20% in the lookup table, the image determination unit 25 determines from the motion determination unit 24. Receive the partial images, calculate the proportion of the partial images which are judged to be motion among these partial images among the whole selected partial images, and when the calculated ratio is 20% or more, determine as moving picture, 20 If it is% or less, it can determine with a still image. In this case, the ratio of the partial images determined to be in motion among the entire selected partial images set in the lookup table should be optimally set through experiments.

As described above, the image determiner 25 determines the type of image based on the ratio of the partial images determined to be in motion among all the partial images, and transmits the gate control signal FLK according to the gate voltage adjuster ( 30). Here, the gate control signal is generated using the GSC of the first timing signal generated from the timing signal generator 21.

Therefore, when the image data is a moving picture, as shown in Fig. 5A, the gate control signal FLK for the still picture in which the entire section (one frame period) is on is output, and when the image data is the still picture, As shown in FIG. 5B, a gate control signal FLK 'for a moving image, which is an ON signal, is output in a first section having a relatively wide section for each GSC period and an off signal in a second section having a relatively narrow section. Here, the second period refers to a period in which the gate voltage transitions to a lower potential at high potential when the gate voltage is later adjusted.

The gate voltage adjuster 30 adjusts the high potential gate voltage by using the first timing signal supplied from the timing signal generator and the gate control signal supplied from the image determiner 25. In this case, the high potential gate voltage is present as a basic waveform of the square wave pulse.

For example, when the gate control signal is a control signal FLK for a moving image, the high potential gate voltage is not adjusted and the square wave pulse is output as it is.

On the contrary, when the gate control signal is the control signal FLK 'for the still image, the gate control signal is adjusted to a high potential gate voltage that is shifted to a lower potential in a predetermined section (ie, the second section) after the square wave pulse.

The high potential gate voltage Vgh adjusted as described above is supplied to the gate driver 40.                     

The gate driver 40 receives the high potential gate voltage Vgh adjusted from the gate voltage adjuster 30 according to the first timing signal generated by the timing signal generator. GL) sequentially.

The data driver 50 converts the image data into a gray voltage corresponding to a gray value according to the second timing signal synchronized with the first timing signal, and supplies the image data to the data lines DL of the liquid crystal panel 60. do.

Accordingly, a predetermined image is displayed on the liquid crystal panel 60 according to the gray scale voltage.

A method of driving a liquid crystal panel using a high potential gate voltage that is adjusted differently according to the type of image in the liquid crystal display device configured as described above will be described.

First, analog image data input from the outside is converted into digital image data by the digital video card 10, and a vertical synchronizing signal Vsync and a horizontal synchronizing signal Hsync are detected from the analog image data.

The converted digital image data is supplied to the frame memory 22, and the detected vertical and horizontal synchronization signals are supplied to the timing signal generator 21.

The timing signal generator 21 generates first and second timing signals for driving the gate driver 40 and the data driver 50 using the vertical and horizontal synchronization signals Vsync.Hsync.

The frame memory 22 temporarily stores the previous image data and the current image data supplied from the digital video card 10 and then supplies them to the partial image selector 23.

The partial image selector 23 selects a predetermined number of partial images to determine a change in motion from the previous image data and the current image data, and supplies them to the motion determiner 24.

The motion determiner 24 compares the partial images of the previous image data selected by the partial image selector 23 with respective pixel values of the partial images of the current image data, and determines whether there is motion. The determination result is supplied to the image determination unit 25.

The image determination unit 25 determines the type of image based on a determination result of whether the movement is supplied from the movement determination unit 24, and the gate control signal FLK, FLK ′ according to the determined result is determined. Supply to the voltage adjusting unit 30.

Accordingly, when the gate control signal is a gate control signal FLK for a moving image, a square wave pulse is output as it is without correcting the high potential gate voltage by the gate voltage adjusting unit 30, and conversely, the gate control signal is In the case of the gate control signal FLK 'for the still image, the gate voltage adjusting unit 30 adjusts the gate voltage to the high potential gate voltage which is transitioned to a lower potential in a predetermined section after the square wave pulse.

The high potential gate voltage Vgh adjusted as described above is supplied to the gate driver 40.

Accordingly, the gate driver 40 may adjust the high potential gate voltage adjusted from the gate voltage adjuster 30 according to the first timing signal generated from the timing signal generator to generate gate lines (eg, gate lines) of the liquid crystal panel 60. GL) is sequentially supplied, while the data driver 50 converts the image data into a gradation voltage according to a gradation value in accordance with the second timing signal synchronized with the first timing signal. By supplying the data lines DL, a predetermined image is displayed on the liquid crystal panel 60.

Accordingly, the present invention compares the previous frame image with the current frame image to determine the image type, adjusts the high potential gate voltage according to the determined image type, and adjusts the adjusted high potential gate voltage to the gate lines GL of the liquid crystal panel. In addition, the image quality can be improved by supplying the gradation voltage corresponding to the image data to the data lines DL of the liquid crystal panel.

As described above, according to the present invention, by applying a different high potential gate voltage according to the type of the image, it is possible to secure more gate charging time in the moving image to improve the gate charging characteristic.

Therefore, by using different high potential gate voltages depending on the type of image in this way, the image quality of the image can be further improved.

Claims (10)

A liquid crystal panel having a plurality of pixels in which gate lines and data lines are arranged in a matrix, and displaying image data on each pixel; The first and second timing signals for driving the liquid crystal panel are generated by using the synchronization signal detected from the image data, and the image type according to the change of movement between the previous frame image and the current frame image of the image data is determined. A control unit; A gate voltage adjuster for adjusting a different high potential gate voltage according to the determined image type; A gate driver for sequentially supplying the adjusted high potential gate voltage to the liquid crystal panel according to the first timing signal; And A data driver for supplying a gray voltage corresponding to the image data to the liquid crystal panel according to the second timing signal, The gate voltage adjusting unit outputs a high potential gate voltage as a square wave pulse as it is when the gate control signal is a signal for a moving image, and when a gate control signal is a signal for a still image, And a high potential gate voltage which is transitioned to a low potential. The method of claim 1, wherein the control unit, A partial image selecting unit for selecting partial images to determine a change in motion from the previous frame image and the current frame image; A motion determination unit for comparing the partial images of the previous frame image and the partial images of the current frame image to determine whether to move; And An image determination unit for determining an image type for the image data by using a distribution ratio of the partial images determined as the movement and outputting different gate control signals accordingly Liquid crystal display comprising a. The lookup table memory according to claim 2, wherein an image type according to a distribution ratio of partial images determined as motion is set as a table. Liquid crystal display further comprising. The liquid crystal display device according to claim 2, wherein the image type is one of a still image or a moving image. delete delete Determining an image type using a previous frame image and a current frame image of image data, wherein the image type is one of a still picture or a moving picture; Adjusting a high potential gate voltage according to the type of the determined image; Sequentially supplying the adjusted high potential gate voltage to a liquid crystal panel; And Supplying a gray voltage for the image data to the liquid crystal panel in synchronization with the adjusted high potential gate voltage, When the image is a moving image, the high potential gate voltage is supplied to the liquid crystal panel as a square wave pulse, and when the image is a stationary image, the high potential gate voltage is transferred to a lower potential in a predetermined section after the square wave pulse. The method of driving a liquid crystal display device, characterized in that is adjusted to the above gate voltage and supplied to the liquid crystal panel. 8. The method of claim 7, wherein the image type is determined based on a change in movement between partial images respectively selected from the previous frame image and the current frame image. delete delete

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