KR20070119140A - Liquid crystal display and driving method thereof - Google Patents

Abstract

A liquid crystal display device and a driving method thereof are provided to improve a visibility transmittance of the display device by generating an impulsive data voltage by adding a normal data voltage to a block data voltage, and applying the impulse data voltage. A liquid crystal display device includes plural pixels(PX), gate and data lines, and a data driver(500). The pixels are arranged in a matrix formation. The gate lines(G1-Gn) and the data lines(D1-Dm) are connected to the pixels. The data driver sequentially applies a normal data voltage and a block data voltage to the data lines during one frame. A second period, during which the block data voltage is applied, is shorter than a first period, during which the normal data voltage is applied.

Description

Liquid crystal display and its driving method {LIQUID CRYSTAL DISPLAY AND DRIVING METHOD THEREOF}

With reference to the accompanying drawings will be described in detail the embodiments of the present invention to make the present invention clear.

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

2 is an equivalent circuit diagram of one pixel of a liquid crystal display according to an exemplary embodiment of the present invention.

3 is a view for explaining a driving method of a liquid crystal display according to an exemplary embodiment of the present invention.

4 is a diagram illustrating a method of expressing impulsive image data according to gray scales in a liquid crystal display according to an exemplary embodiment of the present invention.

<Description of Drawing>

3: liquid crystal layer 100: lower display panel

191: pixel electrode 200: upper display panel

230: color filter 270: common electrode

300: liquid crystal panel assembly 400: gate driver

500: data driver 600: signal controller

800: gray voltage generator

R, G, B: Input image data DE: Data enable signal

MCLK: Main Clock Hsync: Horizontal Sync Signal

Vsync: Vertical Sync Signal CONT1: Gate Control Signal

CONT2: data control signal DAT: digital video signal

Clc: Liquid Crystal Capacitor Cst: Keeping Capacitor

Q: switching device

The present invention relates to a liquid crystal display and a driving method thereof.

A typical liquid crystal display (LCD) includes two display panels provided with pixel electrodes and a common electrode, and a liquid crystal layer having dielectric anisotropy interposed therebetween. The pixel electrodes are arranged in a matrix and connected to switching elements such as thin film transistors (TFTs) to receive data voltages one by one in sequence. The common electrode is formed over the entire surface of the display panel and receives a common voltage. The pixel electrode, the common electrode, and the liquid crystal layer therebetween form a liquid crystal capacitor, and the liquid crystal capacitor becomes a basic unit that forms a pixel together with a switching element connected thereto.

In such a liquid crystal display, a voltage is applied to two electrodes to generate an electric field in the liquid crystal layer, and the intensity of the electric field is adjusted to adjust the transmittance of light passing through the liquid crystal layer to obtain a desired image. In this case, in order to prevent degradation caused by an electric field applied to the liquid crystal layer for a long time, the polarity of the data voltage with respect to the common voltage is inverted frame by frame, row by pixel, or pixel by pixel.

On the other hand, since the LCD is a hold type display device, blurring occurs when an edge of an object is not clear and blurs when a moving image is displayed. In order to reduce blurring, an impulsive driving method for displaying a desired normal image and a black image in the middle thereof has been developed.

However, the impulsive driving method has lower brightness than the black image is inserted because the black image is inserted. In order to improve this, the impulsive data input may be inserted with low grayscale data that is slightly brighter than black data.

However, since this method determines the level of gray level currently input with reference to the previous frame, it requires a frame memory capable of storing one frame of image data and a logic circuit for determining the level of gray level, which increases the cost. It can be a factor.

Accordingly, an object of the present invention is to provide a liquid crystal display and a driving method thereof that can solve the problems of the prior art.

According to an embodiment of the present invention, a liquid crystal display device includes a plurality of pixels arranged in a matrix form, a gate line and a data line connected to the pixels, and a regular data voltage and a black data voltage. And a data driver sequentially applying the data line to the data line for one frame, wherein the second time for applying the black data voltage is shorter than the first time for applying a normal data voltage.

The liquid crystal display may further include a gate driver configured to generate gate-on voltages corresponding to the first and second times, and apply the gate-on voltage to the gate lines, respectively.

In this case, the normal data voltage is maintained for a third time after the first time, and the voltage obtained by adding the black data voltage and the normal data voltage for a fourth time after the second time is maintained as an impulsive data voltage. Can be.

Meanwhile, according to an exemplary embodiment, a driving method of a liquid crystal display device including a plurality of pixels, a gate line and a data line connected to the plurality of pixels may include applying a normal data voltage to the data line at a first time; Maintaining the normal data voltage, applying a black data voltage to the data line at a second time, and maintaining a voltage obtained by adding the black data voltage and the normal data voltage as an impulsive data voltage; The second time is shorter than the first time.

The method may further include generating a gate-on voltage corresponding to the first time and the second time and applying the same to the gate line.

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.

In the drawings, the thickness of layers, films, panels, regions, etc., are exaggerated for clarity. Like parts are designated by like reference numerals throughout the specification. When a portion of a layer, film, region, plate, etc. is said to be "on top" of another part, this includes not only when the other part is "right on" but also another part in the middle. On the contrary, when a part is "just above" another part, there is no other part in the middle.

First, a liquid crystal display according to an exemplary embodiment of the present invention will be described in detail with reference to FIGS. 1 and 2.

1 is a block diagram of a liquid crystal display according to an exemplary embodiment of the present invention, and FIG. 2 is an equivalent circuit diagram of one pixel of the 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 assembly 300, a gate driver 400, a data driver 500, and a data driver 500 connected thereto. The gray voltage generator 800 connected to the signal generator 500 and a signal controller 600 for controlling the gray voltage generator 800 are included.

The liquid crystal panel assembly 300 includes a plurality of signal lines G ₁ -G _n , D ₁ -D _m and a plurality of pixels PX connected to the plurality of signal lines G ₁ -G _n , D ₁ -D _m , and arranged in a substantially matrix form. Include. On the other hand, in the structure shown in FIG. 2, the liquid crystal panel assembly 300 includes lower and upper panels 100 and 200 facing each other and a liquid crystal layer 3 interposed therebetween.

The signal lines G ₁ -G _n and D ₁ -D _m are a plurality of gate lines G ₁ -G _n for transmitting a gate signal (also called a “scan signal”) and a plurality of data lines for transmitting a data signal ( D ₁ -D _m ). The gate lines G ₁ -G _n extend substantially in the row direction and are substantially parallel to each other, and the data lines D ₁ -D _m extend substantially in the column direction and are substantially parallel to each other.

Each pixel PX, for example, the pixel PX connected to the i-th (i = 1, 2,, n) gate line G _i and the j-th (j = 1, 2,, m) data line Dj. ) Includes a switching element Q connected to the signal line G _i D _j , a liquid crystal capacitor Clc, and a storage capacitor Cst connected thereto. Holding capacitor Cst can be omitted as needed.

The switching element Q is a three-terminal element of a thin film transistor or the like provided in the lower panel 100, the control terminal of which is connected to the gate line G _i , and the input terminal of which is connected to the data line D _j . The output terminal is connected to the liquid crystal capacitor Clc and the storage capacitor Cst.

The liquid crystal capacitor Clc has two terminals, the pixel electrode 191 of the lower panel 100 and the common electrode 270 of the upper panel 200, and the liquid crystal layer 3 between the two electrodes 191 and 270 is a dielectric material. Function as. The pixel electrode 191 is connected to the switching element Q, and the common electrode 270 is formed on the front surface of the upper panel 200 and receives the common voltage Vcom. Unlike in FIG. 2, the common electrode 270 may be provided in the lower panel 100. In this case, at least one of the two electrodes 191 and 270 may be formed in a linear or bar shape.

The storage capacitor Cst, which serves as an auxiliary part of the liquid crystal capacitor Clc, is formed by overlapping a separate signal line (not shown) and the pixel electrode 191 provided on the lower panel 100 with an insulator interposed therebetween. A predetermined voltage such as the common voltage Vcom is applied to the separate signal line. However, the storage capacitor Cst may be formed such that the pixel electrode 191 overlaps the front gate line directly above the insulator.

On the other hand, in order to implement color display, each pixel PX uniquely displays one of the primary colors (spatial division) or each pixel PX alternately displays the primary colors over time (time division). The desired color is recognized by the spatial and temporal sum of these primary colors. Examples of the primary colors include three primary colors such as red, green, and blue. FIG. 2 illustrates that each pixel PX includes a color filter 230 representing one of the primary colors in an area of the upper panel 200 corresponding to the pixel electrode 191 as an example of spatial division. Unlike FIG. 2, the color filter 230 may be formed above or below the pixel electrode 191 of the lower panel 100.

At least one polarizer (not shown) for polarizing light is attached to an outer surface of the liquid crystal panel assembly 300.

Referring back to FIG. 1, the gray voltage generator 800 generates two sets of gray voltage sets (or reference gray voltage sets) related to the transmittance of the pixel PX. One of the two sets has a positive value for the common voltage Vcom and the other set has a negative value.

A gate driver 400, a gate line (G ₁ -G _n) and is connected to the gate turn-on voltage (Von), and a gate signal consisting of a combination of a gate-off voltage (Voff), a gate line (G ₁ of the liquid crystal panel assembly 300 -G _n ).

The data driver 500 is connected to the data lines D ₁ -D _m of the liquid crystal panel assembly 300 and selects a gray voltage from the gray voltage generator 800 and uses the data line D ₁ as a data signal. -D _m ). However, when the gray voltage generator 800 provides only a predetermined number of reference gray voltages instead of providing all of the voltages for all grays, the data driver 500 divides the reference gray voltages to divide the gray voltages for all grays. Generate and select the data signal from it.

The signal controller 600 controls the gate driver 400, the data driver 500, and the like.

Each of the driving devices 400, 500, 600, and 800 may be mounted directly on the liquid crystal panel assembly 300 in the form of at least one integrated circuit chip, or may be a flexible printed circuit film (not shown). It may be mounted on the liquid crystal panel assembly 300 in the form of a tape carrier package (TCP) or mounted on a separate printed circuit board (not shown). Alternatively, these driving devices 400, 500, 600, and 800 are integrated in the liquid crystal panel assembly 300 together with the signal lines G ₁ -G _n , D ₁ -D _m and the thin film transistor switching element Q. May be In addition, the driving devices 400, 500, 600, and 800 may be integrated into a single chip, in which case at least one of them or at least one circuit element constituting them may be outside the single chip.

Next, the operation of the liquid crystal display will be described in detail.

The signal controller 600 receives input image signals R, G, and B and an input control signal for controlling the display thereof from an external graphic controller (not shown). Examples of the input control signal include a vertical sync signal Vsync, a horizontal sync signal Hsync, a main clock MCLK, and a data enable signal DE.

The signal controller 600 properly processes the input image signals R, G, and B according to operating conditions of the liquid crystal panel assembly 300 based on the input image signals R, G, and B and the input control signal, and controls the gate. After generating the signal CONT1 and the data control signal CONT2, the gate control signal CONT1 is sent to the gate driver 400, and the data control signal CONT2 and the processed image signal DAT are transmitted to the data driver 500. Export to).

The gate control signal CONT1 includes a scan start signal STV indicating a scan start and at least one clock signal controlling an output period of the gate-on voltage Von. The gate control signal CONT1 may also further include an output enable signal OE that defines the duration of the gate-on voltage Von.

The data control signal CONT2 is a load for applying a data signal to the horizontal synchronization start signal STH and the data lines D ₁ -D _m indicating the start of image data transmission for the pixels PX in one row [bundling]. Signal LOAD and data clock signal HCLK. The data control signal CONT2 is also an inverted signal that inverts the voltage polarity of the data signal relative to the common voltage Vcom (hereinafter referred to as " polarity of the data signal " by reducing the " voltage polarity of the data signal for the common voltage &quot;) RVS) may be further included.

According to the data control signal CONT2 from the signal controller 600, the data driver 500 receives the digital image signal DAT for the pixels PX in one row (bundling), and each digital image signal DAT. By converting the digital image signal DAT into an analog data signal by selecting a gray scale voltage corresponding to), it is applied to the corresponding data lines D ₁ -D _m .

The gate driver 400 applies the gate-on voltage Von to the gate lines G ₁ -G _n in response to the gate control signal CONT1 from the signal controller 600, thereby applying the gate lines G ₁ -G _n . Turn on the switching element (Q) connected to. Then, the data signal applied to the data lines D ₁ -D _m is applied to the pixel PX through the switching element Q turned on.

The difference between the voltage of the data signal applied to the pixel PX and the common voltage Vcom is shown as the charging voltage of the liquid crystal capacitor Clc, that is, the pixel voltage. The arrangement of the liquid crystal molecules varies depending on the magnitude of the pixel voltage, thereby changing the polarization of light passing through the liquid crystal layer 3. The change in polarization is represented by a change in transmittance of light by a polarizer attached to the display panel assembly 300.

This process is repeated in units of one horizontal period (also referred to as "1H" and equal to one period of the horizontal sync signal Hsync and the data enable signal DE), thereby all the gate lines G ₁ -G _n. ), The gate-on voltage Von is sequentially applied to the data signal to all the pixels PX, thereby displaying an image of one frame.

When one frame ends, the state of the inversion signal RVS applied to the data driver 500 is controlled so that the next frame starts and the polarity of the data signal applied to each pixel PX is opposite to the polarity of the previous frame. "Invert frame"). In this case, the polarity of the data signal flowing through one data line is changed (eg, row inversion and point inversion) or the polarity of the data signal applied to one pixel row is different depending on the characteristics of the inversion signal RVS within one frame. (E.g. column inversion, point inversion).

3 is a view illustrating a driving method of a liquid crystal display according to an exemplary embodiment of the present invention, and FIG. 4 is a method of expressing impulsive image data according to gray scales in a liquid crystal display according to an exemplary embodiment of the present invention. It is a figure which shows.

3 illustrates an impulsive driving method of the liquid crystal display according to the exemplary embodiment of the present invention.

According to an exemplary embodiment of the present invention, a liquid crystal display displays a regular image one by one from the first pixel row one by one, and then displays an impulsive image within a predetermined time after displaying the regular image in a predetermined number of pixel rows. For example, display on k pixel rows at the same time. Repeating this for one frame looks as if an impulsive image band with a width of k pixel rows is rotated, as shown.

Therefore, in each pixel row, a normal image is displayed first, followed by an impulsive image.

4 shows an nth frame and a (n + 1) th frame, which is the next frame. In the following, the pixel voltages for the (n + 1) th frame have opposite polarities and the same absolute values. This description is omitted and only the nth frame is described.

In addition, the liquid crystal display according to the exemplary embodiment of the present invention is a normally white mode. As the data voltage is smaller, the image is closer to white, and the data voltage indicating this is called a high gray voltage, and the data voltage is increased. As the image gets closer to black, the data voltage representing this is called a low gray voltage.

4 shows that the data voltages Vd1, Vd2, and Vd3 (hereinafter, referred to as “normal data voltages”) for displaying a normal image gradually increase from top to bottom. In addition, the data voltages Vd1, Vd2, and Vd3 are applied to the pixel PX to show the pixel voltages Vdp1, Vdp3, and Vdp5 that are slightly reduced due to the kick-back voltage.

The nth frame is divided by time T1-T4, the first half T1, T2 is the time for displaying the normal data voltage, and the second half T3, T4 is the data voltage (hereinafter, abbreviated " Impulse data voltage).

That is, if the gray scale is described as an example, the data driver 500 applies the regular data voltage Vd2 to the time T1, and the voltage Vd2 decreases by the kickback voltage and then during the time T2. Is maintained at the pixel voltage Vdp3. Subsequently, the data driver 500 applies the impulsive data voltage Vi2 for a time T3 and is maintained at the pixel voltage Vip3 for a time T4.

Of course, the gate driver 400 generates the gate-on voltage Von for a corresponding time period T1 and T3 during one frame.

At this time, time T3 is shorter than time T1. Therefore, when the impulsive data voltage is applied, the liquid crystal capacitor Clc of the pixel PX may not be sufficiently charged. For example, when an impulsive data voltage of 5V is applied, only about 1V to 2V is charged.

However, the actual impulsive data voltages Vi1, Vi2, and Vi3 are the sum of the previously applied pixel voltages Vdp1, Vdp2, and Vdp3, as shown in the drawing, and the actual charging voltage. Can be.

As a result, the impulsive image is expressed according to the gradation level, and the luminance is not lowered as compared with the case where the black data is completely inserted. In addition, a separate frame memory is not required to apply such an impulsive data voltage, and furthermore, a logic circuit for analyzing a gray level of a previous frame is not required, thereby greatly reducing the cost.

In this way, by applying a value obtained by adding a black data voltage to a previously applied normal data voltage as an impulsive data voltage, an impulsive image according to the gradation level can be expressed without increasing luminance, thereby improving visibility. Furthermore, no frame memory and logic circuits are required, resulting in cost savings.

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.

Claims (5)

A plurality of pixels arranged in a matrix form, A gate line and a data line connected to the pixel, and The data driver sequentially applies a normal data voltage and a black data voltage to the data line for one frame. Including; The second time when the black data voltage is applied is shorter than the first time when a normal data voltage is applied. Liquid crystal display. In claim 1, And a gate driver configured to generate gate on voltages corresponding to the first and second times, and to apply the gate on voltages to the gate lines, respectively. In claim 2, A liquid crystal display in which the normal data voltage is maintained for a third time after the first time, and the voltage of the black data voltage plus the normal data voltage is maintained as an impulsive data voltage for a fourth time following the second time. Device. A driving method of a liquid crystal display device comprising a plurality of pixels, a gate line and a data line connected thereto. Applying a normal data voltage to the data line at a first time; Maintaining the normal data voltage; Applying a black data voltage to the data line at a second time, and Maintaining a voltage obtained by adding the black data voltage and the normal data voltage as an impulsive data voltage Including, The second time is shorter than the first time Driving method of liquid crystal display device. In claim 4, And generating a gate-on voltage corresponding to the first time and the second time and applying the gate-on voltage to the gate line.

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