KR20080063617A - Display apparatus - Google Patents

Abstract

An LCD(Liquid Crystal Display) device is provided to enable a data driver to output a data voltage corresponding to a compensate gray signal, outputted from a gray signal generator, to associated pixels, thereby improving the response rate of the LCD device without an additional process or a change of circuit design. A gray signal generator(400) receives plural original gray signals corresponding to an external image signal in each frame in order, compares a first original gray signal received in an n-2-numbered frame, the first original gray signal received in an n-1-numbered frame, and a second original gray signal received in an n-numbered frame, and outputs the first original gray signal received in the n-1-numbered frame as a compensated compensation gray signal when the gray value of the first original gray signal and the gray value of the second original gray signal are different. A data driver(300) outputs a data voltage swing more than at least one cycle in correspondence to the compensation gray signal. A gate driver(200) outputs a scan signal successively. A display panel(100) includes plural gate lines(GL), plural data lines(DL), and plural pixels(PX). The gate lines receive the scan signal from the gate driver. The data lines receive the data voltage from the data driver. The pixels are connected to the gate lines and the data lines respectively to receive the data voltage in response to the scan signal.

Description

 Display device {DISPLAY APPARATUS}

In order to more fully understand the drawings used in the detailed description of the invention, a brief description of each drawing is provided.

1 is a diagram illustrating an equivalent circuit of each pixel in a liquid crystal display.

2 is a diagram illustrating a data voltage and a pixel voltage applied by a general driving method.

3 illustrates a transmittance of a liquid crystal display according to a general driving method.

4 is a view showing a method of applying a data voltage according to the present invention.

5 is a waveform diagram showing a result of actually simulating a waveform of a data voltage according to the present invention.

FIG. 6 is an enlarged view of a portion A shown in FIG. 5.

7 is a view for explaining a liquid crystal display device according to the present invention.

The present invention relates to a liquid crystal display device, and more particularly, to a liquid crystal display device for high-speed response of liquid crystals.

In general, a liquid crystal display (LCD) includes a liquid crystal panel and a driving circuit for driving the liquid crystal panel. The liquid crystal panel includes two substrates and a liquid crystal material provided between the two substrates and having anisotropic dielectric constant. The liquid crystal display device displays a desired image by applying an electric field to the liquid crystal substance and adjusting the intensity of the electric field.

In recent years, as the liquid crystal display device is used not only for computer monitors but also for TV monitors, the necessity of realizing moving images increases. However, the liquid crystal display has a disadvantage in that it is difficult to implement a moving image because of a slow response speed.

In order to solve the problem of slow response speed, an OCB (Optically Compensated Band) mode is used, a Ferro-Electric Liquid Crysrtal (FLC) material is used, or an overvoltage is applied at an initial stage of driving the liquid crystal. method) has been developed.

However, liquid crystal displays developed to improve the problem of slow response speed as described above require additional process and circuit design changes. As a result, such additional process and circuit design changes increase the production cost of the liquid crystal display.

Accordingly, an object of the present invention is to provide a liquid crystal display device capable of improving the response speed of liquid crystals without changing the additional process or circuit design.

The display device of the present invention for achieving the above technical problem includes a gray signal generator, a data driver, a gate driver and a display panel. The gradation signal generator sequentially receives an original gradation signal corresponding to an image signal from the outside every frame. The gradation signal generator is the first raw gradation signal received in the n-2th frame (where n is a natural number of 3 or more) and the first raw gradation signal received in the n-1th frame and the first received in the nth frame. Compensating the first raw gray level signal received in the n-1th frame when the gray level value of the first raw gray level signal and the second gray level signal of the second raw gray level signal are different from each other by comparing two raw gray level signals. Output as a gradation signal. The data driver corresponds to the corrected gray level signal and outputs a data voltage that swings for at least one period. The gate driver sequentially outputs scan signals. The display panel is connected to the plurality of gate lines receiving the scan signal from the gate driver, the plurality of data lines receiving the data voltage from the data driver, and the gate line and the data line, respectively. A plurality of pixels to receive the data voltage in response to the signal.

According to the display device according to the present invention, when the first and second raw gray level signals have different values, a corrected gray level signal correcting the first raw gray level signal received in the n−1th frame is output. The data driver outputs a data voltage corresponding to the correction gray level signal to the corresponding pixel. Here, this data voltage is a minute voltage that provides a slight impact on the liquid crystal so that it can be easily changed from black gray (or white gray) to white gray (or black gray). Therefore, the response speed of the liquid crystal display device is improved without changing the additional process or circuit design.

In order to fully understand the present invention, the operational advantages of the present invention, and the objects achieved by the practice of the present invention, reference should be made to the accompanying drawings which illustrate preferred embodiments of the present invention and the contents described in the accompanying drawings. In understanding the drawings, it should be noted that like parts are intended to be represented by the same reference numerals as much as possible. Incidentally, detailed descriptions of well-known functions and configurations that are determined to unnecessarily obscure the subject matter of the present invention will be omitted.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

In general, the liquid crystal display includes a plurality of gate lines that transmit scan signals and data lines that cross the gate lines and transmit data voltages. In addition, the liquid crystal display includes a plurality of pixels formed in a region surrounded by the gate lines and the data lines, and connected to each other through the gate lines, the data lines, and the switching elements.

In the liquid crystal display, 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 such a liquid crystal display is shown in FIG. 1.

As illustrated in FIG. 1, each pixel PX of the liquid crystal display includes a TFT 10 having a source electrode SE and a gate electrode GE connected to the data line DL and the gate line GL, respectively. The liquid crystal capacitor Clc is connected between the drain electrode DE of the TFT and the common voltage Vcom and the storage capacitor Cst is connected to the drain electrode DE of the TFT.

In the operation of each pixel, the gate on signal VON is applied to the gate line GL to turn on the TFT 10. At this time, the data voltage Vd supplied to the data line DL is applied to each pixel electrode PE through the TFT 10. Then, an electric field corresponding to the difference between the pixel voltage Vp and the common voltage Vcom applied to the pixel electrode PE is applied to the liquid crystal (equivalently represented by the liquid crystal capacitor in FIG. 1) to correspond to the intensity of the electric field. Light is transmitted at a transmittance to In this case, the pixel voltage Vp should be maintained for one frame. In FIG. 1, the storage capacitor Cst is used to maintain the pixel voltage Vp applied to the pixel electrode PE.

On the other hand, since the liquid crystal has an anisotropic dielectric constant, there is a characteristic that the dielectric constant is different depending on the direction of the liquid crystal. That is, when the director of the liquid crystal changes as the voltage is applied, the dielectric constant also changes accordingly, and thus the capacitance of the liquid crystal capacitor (hereinafter referred to as liquid crystal capacitance) also changes.

Once the charge is supplied to the liquid crystal capacitor during the period in which the TFT 10 is turned on, the TFT 10 is turned off. Since Q = CV, the pixel voltage Vp applied to the liquid crystal when the liquid crystal capacitance changes is also Change together.

Normally white mode TN (twisted Nematics) liquid crystal display, for example, when the pixel voltage supplied to the pixel is 0V, the liquid crystal capacitance is arranged in a direction parallel to the substrate, so that the liquid crystal capacitance is C ( 0V) = ε _┴ A / d. Here, ε _을 represents the permittivity when the liquid crystal molecules are arranged in a direction parallel to the substrate, that is, when the liquid crystal molecules are arranged in a direction perpendicular to the direction of the light, and A and d are the area of the liquid crystal display substrate, respectively. The distance between the substrates is shown.

Assuming that the voltage for realizing full black is 5V, when 5V is applied to the liquid crystal, the liquid crystal molecules are arranged in a direction perpendicular to the substrate, so that the liquid crystal capacitance is C (5V) = ε _┴ A / d. .

In the case of the liquid crystal used in the TN mode, since ε _∥ − ε _┴ > 0, the higher the pixel voltage applied to the liquid crystal, the larger the liquid crystal capacitance.

The amount of charge that the TFT 10 must charge to make full-black in the nth frame is C (5V) × V. However, assuming full-white (V _{n -1} = 0 V) in the n-1th frame, which is the previous frame, the liquid crystal capacitance becomes C (0 V) since the liquid crystal does not respond during the turn-on time of the TFT. Therefore, even if the data voltage Vd of 5V is applied in the nth frame to make full-black, the amount of charge charged in the actual pixel is C (0V) × 5V, and C (0V) <C (5V). The pixel voltage Vp actually supplied is applied with a pixel voltage less than 5V (for example, 3.5V), so that full-black is not implemented.

In addition, when the data voltage Vd is applied at 5V to implement full-black in the next frame, the n + 1th frame, the amount of charge charged in the liquid crystal becomes C (3.5V) × 5V, which is eventually supplied to the liquid crystal. The voltage Vp becomes between 3.5V and 5V. If this process is repeated, the pixel voltage Vp reaches a desired voltage after several frames.

In terms of gray scale, when a signal (pixel voltage) applied to an arbitrary pixel is changed from low gray scale to high gray scale (or from high gray scale to low gray scale), the gray scale of the current frame is affected by the gray scale of the previous frame. Because it does not receive the desired gradation immediately, it does not reach the desired gradation until a few frames have elapsed. Similarly, the transmittance of the pixel of the current frame is influenced by the transmittance of the pixel of the previous frame to obtain the desired transmittance after a few frames have elapsed.

On the other hand, if n-1 frame is full-black, that is, the pixel voltage (Vp) is 5V, and a data voltage of 5V is applied to implement full-black in n frame, the liquid crystal capacitance is C (5V) The charge amount corresponding to C (5V) × 5V is charged, and thus the pixel voltage Vp of the liquid crystal is 5V.

As such, the pixel voltage Vp actually supplied to the liquid crystal is determined not only by the data voltage supplied to the current frame but also by the pixel voltage Vp of the previous frame.

2 is a diagram illustrating a data voltage and a pixel voltage when applied in a general driving method.

Referring to FIG. 2, the data voltage Vd corresponding to the target pixel voltage Vw is applied every frame without comparing the pixel voltage Vp of the previous frame. Therefore, as described above, the pixel voltage Vp actually applied to the liquid crystal is lower or higher than the target pixel voltage by the liquid crystal capacitance corresponding to the pixel voltage of the previous frame. Therefore, the target pixel voltage is only reached after a few frames.

3 illustrates a transmittance of a liquid crystal display according to a general driving method.

Referring to FIG. 3, since the actual pixel voltage is lower than the target pixel voltage as described above, even when the response time of the liquid crystal is within one frame, the target transmittance may not be reached until several frames have passed.

However, in the present invention, as the image signal Pn of the current frame is input, the following correction signal Pn 'is obtained by comparing the image signal Pn-1 of the previous frame with the image signal Pn + 1 of the next frame. ) Is applied, and the corrected image signal Pn 'is applied to each pixel. Here, the image signal Pn means a data voltage when the liquid crystal display adopts an analog driving method, but a gray level signal (or gradation data) that is binary to control the data voltage when the digital driving method is adopted. Since the correction of the voltage applied to the actual pixel is performed through the correction of the gray level signal.

4 is a diagram showing a method of applying a data voltage according to the present invention, FIG. 5 is a diagram showing a result of simulating a waveform of a data voltage according to the present invention shown through measurement equipment, and FIG. 6 is shown in FIG. An enlarged view of the portion A shown.

Referring to FIG. 4, the present invention compares the target pixel voltage of the nth frame with the pixel voltage (or data voltage) of the (n-1) th frame and the pixel voltage of the (n + 1) th frame. The data voltage Vn 'is applied accordingly so that the pixel voltage Vp of the current frame immediately reaches the target pixel voltage.

In more detail, when the nth frame changes from black gray to white gray, an abnormal data voltage according to the present invention higher than the black gray in one frame before converting to white gray, that is, in the (n-1) th frame. A small impact is applied to the liquid crystal for a short time.

The abnormal data voltage is not a voltage level enough to form a pretilt angle on the liquid crystal molecules, but the liquid crystal molecules are excited by providing a fine impact to the liquid crystal molecules for a very short time. As such, the liquid crystal molecules excited in the activated state can more easily reach the target pixel voltage.

5 and 6, the data voltage according to the present invention has a form of an AC voltage swinging at least one cycle. The AC voltage may be an AC voltage having a positive impulse and a negative impulse type. The peak voltage Vpeak of the AC voltage may be set to be 5% to 10% higher than the data voltage Vblack corresponding to the lowest gray level, for example, the black gray level. In addition, one cycle T1 of the AC voltage is preferably set to 50% or less of one frame period.

The data voltage applied to the liquid crystal in the n−1 th frame may be set to correspond to the black gradation set independently of gray, or may be set to have different values to correspond to each gray.

That is, when the gray scale is changed from the nth frame, the response speed of converting the black gray to the white gray can be increased.

For example, if the (n-2) th frame is black or dark gradation and the nth frame is white or light gradation, even if the signal corresponding to the (n-1) th frame is black gradation (n-1) The correct gradation signal, not the black gradation, is applied to the first frame. Then, the n-th frame can reach the target pixel voltage, that is, the white gray level, more quickly.

As such, in response to the gray level signal changing from black gray to white gray, the response speed of the liquid crystal may be increased by outputting a data voltage corresponding to the corrected gray level signal for providing a minute shock to the liquid crystal for a very short time.

7 is a view for explaining a liquid crystal display device according to the present invention.

Referring to FIG. 7, the liquid crystal display according to the present invention includes a liquid crystal display panel 100, a gate driver 200, a data driver 300, and a gray signal generator 400. Here, the gate driver 200, the data driver 300, and the gray level signal generator 400 convert the image signal provided from an external host system such as a graphic controller to be adapted to the liquid crystal display panel 100 and output the liquid crystal. The operation is performed as a driving device of the display device.

A plurality of gate lines DLs are formed in the liquid crystal display panel 100 to transfer gate-on signals, and a plurality of data lines DLs are provided to transfer data voltages corresponding to the correction gray level signals. Each of the regions surrounded by the gate line GL and the data line DL constitutes a pixel, and each pixel includes a gate electrode GE and a source electrode at the gate line GL and the data line DL, respectively. The TFT includes a thin film transistor 110 connected to the SE, a liquid crystal capacitor Clc connected to the drain electrode DE of the thin film transistor 110, and a storage capacitor Cst.

In particular, the liquid crystal display panel 100 may adopt a twisted nematic (TN) mode, a vertical alignment (VA) mode, or a patterned vertical alignment (PVA). An alignment mode may be employed, or a mixed vertical alignment (MVA) mode may be employed.

The gate driver 200 sequentially applies gate-on voltages VON (S1, S2, S3, ..., Sn) to the gate line GL, and applies the gate-on voltage to the gate line GL to which the gate-on voltage is applied. The thin film transistor 110 to which the gate electrode GE is connected is turned on.

The data driver 300 respectively converts the data signals D1, D2,..., And Dm from which the correction gray level signal Gn'-1 received from the gray level signal generator 400 to the corresponding data voltage are respectively included in the data line ( DL).

The gray level signal generator 400 receives the original gray level signal Gn of the nth frame, and then compares and corrects the data gray level signals of the n-1 th frame, the n-2 th frame, and the n th frame as described above. The gray level signal Gn'-1 is output.

For example, the first raw gray level signal Gn-2 of the n-2th frame, the first raw gray level signal Gn-1 of the n-1th frame, and the second raw gray level signal of the nth frame ( When Gn) is sequentially received and the first raw gray level signal Gn-1 and the second raw gray level signal Gn have the same value, the first raw gray level signal Gn− of the n−1th frame is received. 1) is not corrected.

The first raw gray level signal Gn-2 of the n-2th frame and the first raw gray level signal Gn-1 of the n-1th frame correspond to the black gray level, and the second raw gray level signal of the nth frame ( When Gn) corresponds to the white gray scale, that is, when the first raw gray level signal Gn-2 and the second raw gray level signal Gn have different values, the first raw gray level of the n-1th frame The signal Gn-1 is corrected to a data voltage that can give a slight impact to the liquid crystals. This data voltage does not function as a voltage including image signal information, which may deteriorate the display quality of the display device. However, one frame is not recognized because it is a very short time.

Meanwhile, although the gradation signal generator 400 is illustrated as being independently present in the drawing, the gradation signal generator 400 may be integrated into a graphic card, a liquid crystal display module, a timing controller, or a data driver.

As described above, according to the present invention, the pixel voltage can reach the target voltage level by correcting the data voltage and applying the corrected data voltage to the pixel. Therefore, the response speed of the liquid crystal can be improved without changing the structure of the liquid crystal display panel or changing the complicated circuit design, so that a moving picture or the like can be usefully displayed.

According to the display device of the present invention as described above, the gradation signal generator is configured to output the first raw gradation signal of the n-2th frame, the first raw gradation signal of the n-1th frame and the second raw gradation signal of the nth frame. It sequentially receives and compares the first and second raw gray level signals. In this case, when the first and second raw gray level signals have different values, a corrected gray level signal corrected by the first raw gray level signal received in the n−1th frame is output. On the other hand, the data driver outputs a data voltage corresponding to the corrected gradation signal to the corresponding pixel. Here, this data voltage is a minute voltage that provides a slight impact on the liquid crystal so that it can be easily changed from black gray (or white gray) to white gray (or black gray).

Therefore, the response speed of the liquid crystal display device is improved without changing the additional process or circuit design.

As described above, the optimum embodiment has been disclosed in the drawings and the specification. Although specific terms have been used herein, they are used only for the purpose of describing the present invention and are not intended to limit the scope of the present invention as defined in the claims or the claims. Therefore, those skilled in the art will understand that various modifications and equivalent other embodiments are possible. Therefore, the true technical protection scope of the present invention will be defined by the technical spirit of the appended claims.

Claims (5)

A plurality of raw gradation signals corresponding to an image signal are received sequentially from the outside every frame, and the first raw gradation signal received in the n-2 th frame (where n is a natural number of 3 or more) and the n-1 th frame When the gray level value of the first raw gray level signal and the gray level value of the second raw gray level signal are different from each other by comparing the received first raw gray level signal with the second raw gray level signal received in the nth frame, the n− A gradation signal generator for outputting the first gradation signal received in the first frame as a corrected gradation signal; A data driver corresponding to the corrected gray level signal and outputting a data voltage swinging at least one cycle; A gate driver sequentially outputting scan signals; And A plurality of gate lines receiving the scan signal from the gate driver, a plurality of data lines receiving the data voltage from the data driver, and a gate line and the data line, respectively, in response to the scan signal And a display panel including a plurality of pixels to receive the data voltage. The display device of claim 1, wherein the data voltage is an alternating voltage comprising a positive impulse voltage and a negative impulse voltage.  The display device of claim 2, wherein the peak voltage of the AC voltage is 5% to 10% higher than the data voltage corresponding to the lowest gray level. The display device of claim 2, wherein one period of the data voltage is 50% or less of one frame period. The gray level value of the first raw gray level signal and the second gray level signal of the second raw gray level signal are the same, and the gray level value of the corrected gray level signal is the same as the gray level value of the second raw gray level signal. Display device.

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