KR20030097247A - A Liquid Crystal Display and A Driving Method Thereof - Google Patents

Abstract

PURPOSE: A liquid crystal display device and a method for driving the same are provided to display patterns for removing after images by a set period even when equal image data is continuously displayed for a predetermined time. CONSTITUTION: A liquid crystal display device includes an LCD panel(1), gate and data driving parts(2,3), a driving voltage generating part(4), a timing control part(5) and a gray voltage generating part(6). The timing control part outputs digital signals for driving the gate and data driving parts by receiving R,G,B data signals, vertical and horizontal synchronizing signals and main clock signals. If image data(R,G,B) are provided from a graphic controller for a predetermined time, the timing control part provides the data driving part with image data corresponding to after-image removing pattern instead of the image data, thereby preventing the after image generation.

Description

A liquid crystal display and a driving method thereof

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 that minimize afterimages.

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 is a display device that obtains a desired image signal by applying an electric field to a liquid crystal material having an anisotropic dielectric constant injected between two substrates, and controlling the amount of light transmitted through the substrate by adjusting the intensity of the electric field. Such LCDs are typical among portable flat panel displays, and among them, TFT LCDs using thin film transistors (TFTs) as switching elements are mainly used.

The liquid crystal display device is used not only for displaying still images but also for displaying moving images. However, when a moving image is displayed or when an image of the same pattern is displayed for a predetermined time, an afterimage occurs due to the characteristics of the liquid crystal. The afterimage represents a phenomenon in which, when displaying an image of one frame and then displaying an image of the next frame, the screen pattern of the previous frame does not disappear and remains intact to affect the display of the image of the current frame.

Afterimage is one of the defects that significantly affect the visibility because the existing screen pattern affects the new screen. Factors affecting afterimages include various concentrations of ion impurities in the liquid crystal, strength of alignment force, kickback phenomenon, and the like.

For example, when the concentration of the ionic impurities is not appropriate and the ionic impurities present in the liquid crystal in the volume are adsorbed onto the polyimide film for some reason, the residual DC voltage remains even in the state where the gradation voltage is not applied. Therefore, when this residual DC voltage acts on the liquid crystal molecules, the image remains in the liquid crystal panel and an afterimage occurs.

For this reason, liquid crystal display devices have been manufactured in such a way as to optimally control the concentration of ionic impurities in the liquid crystal and increase the orientation force as much as possible, and improve the driving method of the liquid crystal display device to reduce the kickback voltage. Efforts have been made to improve the response speed of liquid crystals.

However, only reducing the amount of kickback voltage has a limit in removing the afterimage.

Therefore, the technical problem to be achieved by the present invention is to solve the conventional problem, and to minimize the afterimage in the liquid crystal display device more efficiently.

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

2 is a flowchart for preventing afterimage generation according to an exemplary embodiment of the present invention.

3A to 3C illustrate examples of pattern display for removing an afterimage according to an exemplary embodiment of the present invention.

According to an aspect of the present invention, a liquid crystal display device includes a plurality of gate lines, a plurality of data lines insulated from and intersecting the plurality of gate lines, and an area in which the gate lines and the data lines cross each other. A liquid crystal panel formed on the liquid crystal panel and including a plurality of pixels each having a switching element connected to the gate line and the data line; A gate driver configured to apply a gate voltage to turn on / off the switching element to the gate line; And a data driver for applying a gray voltage representing image data to the data line, wherein the data driver is provided with grayscales according to image data corresponding to an afterimage removing pattern when the same image data is continuously applied for a predetermined time. The voltage is supplied to the data line.

In particular, the apparatus may further include a timing controller configured to provide image data applied from the outside to the data driver and to drive the gate driver to apply the gray voltage through the data line to a pixel connected to the gate line.

In this case, the timing controller may include a storage unit which stores image data corresponding to at least one image retention pattern; A counter for counting the time for which the same image data is applied from the outside; And a controller configured to provide image data corresponding to one afterimage removing pattern stored in the storage unit to the data driver during a setting period when the counted time passes a set time.

In addition, a method of driving a liquid crystal display according to another aspect of the present invention may include a plurality of gate lines, a plurality of data lines that are insulated from and cross the plurality of gate lines, and are formed in an area where the gate lines and the data lines cross each other. A driving method of a liquid crystal display including a plurality of pixels each having a switching element connected to the gate line and the data line, the method comprising: supplying a gray voltage corresponding to image data applied to the data line; Supplying a gate voltage to the gate line to apply the gray voltage to the pixel; And supplying a gray scale voltage according to the image data corresponding to the afterimage removing pattern to the data line during the setting period, when the image data is the same for the set time.

In the present invention having such characteristics, the afterimage removing pattern includes at least one of a black pattern, a white pattern, and a 32 gray pattern.

DETAILED DESCRIPTION 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.

1 illustrates a structure of a liquid crystal display according to an exemplary embodiment of the present invention.

As shown in FIG. 1, a liquid crystal display according to an exemplary embodiment of the present invention includes a liquid crystal panel 1, a gate driver 2, a data driver 3, a driving voltage generator 4, and a timing controller 5. ) And the gray voltage generator 6.

The liquid crystal panel 1 includes two substrates (eg, a TFT substrate and a color filter substrate), and a plurality of data lines and a plurality of gate lines cross each other on one substrate, and one gate line and one data line. Pixels are formed in each of these intersecting regions. Each pixel includes a TFT which is a switching element in which a gate electrode, a source electrode, and a drain electrode are respectively connected to a gate line, a data line, and a pixel electrode.

The timing controller 5 is an R (red), G (green), B (blue) data signal, a vertical synchronization signal (Vsync) that is a frame discrimination signal, and a row discrimination signal from a graphic controller (not shown) outside the LCD module. The digital synchronization signal Hsync and the main clock signal CLK are received to output a digital signal for driving the gate driver 2 and the data driver 3.

The timing signal output from the timing controller 5 to the gate driver 2 includes a vertical start signal Vstart for instructing the gate on voltage to be applied to the gate line, and the gate on voltage. There are a gate clock signal (CPV signal) for sequentially applying to each gate line, and a gate on enable signal OE for enabling the output of the gate driver 2.

In the timing signal output from the timing controller 5 to the data driver 3, the digital data signals R (0: N), G (0: N) and B (0: N), which are passed from the graphics controller, are data. A horizontal start signal Hstart for inputting to the driver 3, a signal for commanding the panel to apply an analog data signal converted in the data driver 3 (hereinafter referred to as a "LOAD signal"), and There is a horizontal clock signal HCLK for data shift in the data driver 3.

In particular, in the embodiment of the present invention, the timing controller 5 receives the same digital data from the graphic controller for a predetermined time, that is, the image data [R (0: N), G (0: N), B (0: N)]. When provided, the image data corresponding to the afterimage removal pattern is provided to the data driver 3 to be displayed instead of the input image data in order to prevent the occurrence of an afterimage.

The afterimage removal pattern according to an embodiment of the present invention includes a black pattern, a white pattern, and a 32 gradation pattern, and the timing controller 5 selects and displays one of the afterimage removal patterns. However, the afterimage removal pattern according to the embodiment of the present invention is not limited to the above-described one, and a pattern composed of image data having a different value from the input image data may be used.

To this end, as shown in FIG. 1, the timing controller 5 according to an exemplary embodiment of the present invention may include a first frame memory 51 in which previous image data is stored, and a second frame memory in which image data currently input ( 52, a pattern storage unit 53 for storing the afterimage removal pattern, a counter 54 for counting a time for inputting the same image data, and a controller 55 for performing a data processing operation or the like. .

On the other hand, the data driver 3 is also called a source driver, and serves to lower the voltage value transferred to each pixel in the liquid crystal panel 1 by one line. More specifically, the data driver 3 stores the digital data (data corresponding to the image data or the image retention pattern) from the timing controller 5 in a shift register in the data driver, and when the LOAD signal is received, the respective data. It selects a voltage corresponding to and transfers this voltage into the liquid crystal panel 1.

The gate driver 2 is also called a scan driver, and serves to open a way for data from the data driver 3 to be transferred to the pixel. Each pixel of the liquid crystal panel 1 is turned on or off by a TFT serving as a switch, and the TFT is turned on or off by applying a constant voltage (Von, Voff) to a gate. The gate driver 2 receives the CPV signal and the 0E signal output from the timing controller 5, and applies gate-on voltages G1, G2,..., Gn to the gate line in synchronization with the two signals CPV, OE. Apply sequentially.

The gray voltage generator 6 generates a gray voltage equally divided according to the number of bits of RGB data provided from a graphic controller (not shown) and provides it to the data driver 3. The data driver 3 is driven by a signal output from the timing controller 5 to apply the data voltages D1, D2,..., Dm to all data lines in synchronization with the driving of the gate driver 2.

On the other hand, the Von voltage for turning on the gate of the TFT and the Voff voltage for turning off the gate are generated in the driving voltage generator 4. The driving voltage generator 4 generates not only the above-mentioned Von and Voff voltages but also a Vcom voltage which is a reference for the data voltage difference in the TFT, and the Vcom voltage is provided to the common electrode of each pixel.

Next, the operation of the liquid crystal display device of the present invention having such a structure will be described in detail.

2 is a flowchart illustrating a processing of a timing controller for removing afterimages according to an exemplary embodiment of the present invention.

First, when image data, a vertical synchronizing signal Vsync as a frame discrimination signal, a horizontal synchronizing signal Hsync as a row discrimination signal, and a main clock signal CLK are provided from a graphic controller (not shown) external to the LCD module. The controller 55 of the timing controller 5 generates various timing signals necessary for driving the liquid crystal, for example, a gate driving clock CPV and a horizontal sync pulse STV, and provides image data to the data driver 3. do.

That is, as shown in FIG. 2, the control unit 55 may include previously transmitted image data stored in the first frame memory 51 before processing and transmitting image data provided from an external graphic controller. By comparison, it is determined whether the image data currently input is the same as the previous image data (S100 to S120).

If the currently input image data is the same as the previous image data, it is determined whether the time at which the same image data input starts to be made exceeds the set time (S130).

Here, the counter 53 of the timing controller starts counting the time from the input time point when the same image data as the previous image data is input, and the set time is continuously displayed from the time point at which the same image data is input, resulting in an afterimage. It's time to get there. In the embodiment of the present invention, after the same image data is continuously displayed for 10 minutes or more, afterimages have started to occur, and a setting time for determining whether the afterimages have occurred is set to 10 minutes. However, this is only one example and may vary depending on the type of liquid crystal display or the experimental environment.

In the above step (S130), when the time at which the same image data input starts to be made exceeds the set time, the controller 55 may include a black pattern, a white pattern, and a residual image removing pattern stored in the pattern storage unit 54. One of the 32 gray patterns is selected and provided to the data driver 3 for display during the set period (S140). However, if the time at which the same image data input starts to be made does not exceed the set time, the input image data is provided to the data driver 3 to be displayed (S150).

In general, the liquid crystal display displays 64 gray levels, and in the embodiment of the present invention, the 32 gray pattern is used as the afterimage removal pattern, but is not necessarily limited thereto.

In detail, the controller 55 provides the input image data to the data driver 3, and if the set time is exceeded, the controller 55 transmits the image data corresponding to the afterimage removing pattern to the data driver 3 for a setting period, for example, about 2 seconds. to provide.

Accordingly, the data driver 3 converts the image data into corresponding data voltages in synchronization with the horizontal start signal Hstart, and then applies them to the source electrodes of the TFTs of the liquid crystal panel 1 in accordance with the applied load signal. The gate driver 2 applies a gate-on voltage to the gate electrode of the TFT in synchronization with the gate clock signal output from the timing controller 5, and as a result, the data voltage applied to the source electrode is charged in the pixel electrode.

Accordingly, the alignment state of the liquid crystals is changed according to the potential difference between the data voltages supplied to the common electrode and the pixel electrode, and thus the light transmission amount is changed to display a desired image, that is, a pattern for removing an afterimage.

As a result, as voltages different from the previous voltage accumulated in each pixel of the liquid crystal panel 1 are applied as the same image data is continuously displayed before, a voltage refresh effect is generated and an afterimage occurs. Is prevented.

Specifically, namely, the voltage of the image data input to the source electrode of the TFT of each pixel is accumulated in the liquid crystal cell and the capacitor from the time when the gate-on voltage for turning on the TFT is applied. The accumulated voltage must be maintained until the next frame, and is discharged by a parasitic capacitor generated by the overlapping chip of the source electrode and the gate electrode, and the DC voltage is offset and applied to the liquid crystal cell by the discharged voltage. When a DC voltage is applied to the liquid crystal cell, impurities in the liquid crystal layer are ionized, and cationic impurities are stacked on the alignment film having a negative polarity, and anion impurities are stacked on the alignment film having a positive polarity, and thus adsorbed to the alignment film as time passes. Because of the ions adsorbed on the alignment layer, the liquid crystal molecules have a direct current voltage, and the voltage acts as a residual direct current voltage. Since the residual DC voltage changes the arrangement direction of the molecules by changing the pretilt angle, which is an optical parameter of the liquid crystal molecules in the liquid crystal cell, the liquid crystal molecules do not react sensitively to the signal voltage applied from the outside. If is displayed for a long time, even if the display screen is changed, the trace of the initial screen remains by the accumulated charge.

However, according to an embodiment of the present invention and as described above, when a predetermined time elapses even when displaying the same image, an image signal having a different pattern is applied to the liquid crystal cell to prevent the voltage of the image data to be displayed in the liquid crystal cell from accumulating. do.

3A to 3C show examples of the pattern display for removing an afterimage.

For example, as shown in Fig. 3A, a black pattern is displayed for two seconds in the middle of the same image display, a white pattern is displayed as shown in Fig. 3B, or a 32 gray pattern is displayed as shown in Fig. 3C.

Therefore, even when the signal display of the same image is performed, image display corresponding to a different pattern is performed for a predetermined time, whereby afterimage generation due to the same image signal display can be suppressed.

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, after the same image data is continuously displayed for a predetermined time, the afterimage can be removed by displaying the afterimage removal pattern for each set period.

Therefore, a remarkable image quality improvement effect of the liquid crystal display device can be obtained.

Claims (5)

A plurality of gate lines, a plurality of data lines insulated from and intersecting the plurality of gate lines, and a plurality of switching elements formed in a region where the gate lines and the data lines intersect, and connected to the gate lines and the data lines, respectively. A liquid crystal panel including pixels; A gate driver configured to apply a gate voltage to turn on / off the switching element to the gate line; And A data driver for applying a gray voltage representing image data to the data line Including; And the data driver is configured to supply the grayscale voltage corresponding to the image data corresponding to the afterimage removal pattern to the data line when the same image data is continuously applied for a predetermined time. The method of claim 1, And a timing controller configured to provide image data applied from the outside to the data driver and to drive the gate driver to apply a gray voltage through the data line to a pixel connected to the gate line. The timing controller, A storage unit which stores image data corresponding to at least one image retention pattern; A counter for counting the time for which the same image data is applied from the outside; And When the counted time has passed the set time, the control unit for providing the image data corresponding to the one image remaining image removal pattern stored in the storage unit to the data driver during the set period Liquid crystal display comprising a. The method according to claim 1 or 2, The afterimage removal pattern may include at least one of a black pattern, a white pattern, and a 32 gray pattern. A plurality of gate lines, a plurality of data lines insulated from and intersecting the plurality of gate lines, and a plurality of switching elements formed in a region where the gate lines and the data lines intersect, and connected to the gate lines and the data lines, respectively. In the driving method of the liquid crystal display device containing a pixel, Supplying a gray voltage corresponding to image data applied to the data line; Supplying a gate voltage to the gate line to apply the gray voltage to the pixel; And If the image data is the same continuously for a set time, supplying a gradation voltage according to the image data corresponding to the afterimage removing pattern to the data line during the set period. Method of driving a liquid crystal display comprising a. The method of claim 1, The afterimage removal pattern includes at least one of a black pattern, a white pattern, and a 32 gray pattern.