KR101096708B1 - Liquid crystal display and driving method thereof - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device and a driving method thereof for reducing the deterioration of image quality when the response characteristics of a liquid crystal are accelerated. The first modulation data is generated according to first source data corresponding to a first period. A data modulator for generating second modulated data according to the second source data and the first modulated data corresponding to a second period immediately after one period; A liquid crystal display device comprising a liquid crystal display panel for displaying data modulated by the first modulated data in the first period and displaying data modulated by the second modulated data in the second period.

Description

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

1 is a waveform diagram showing a change in luminance according to data in a conventional liquid crystal display.

2 is a waveform diagram showing an example of a luminance change caused by data modulation in the high speed driving method.

3 is a circuit diagram showing an example of a high speed drive device.

4 is a diagram showing the transient response of the liquid crystal resulting from the modulated data causing the liquid crystal cell to reach the target luminance in less than one frame period.

FIG. 5 is a diagram showing complementary color distortion in a scroll image due to the transient response of the liquid crystal as shown in FIG. 4.

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

FIG. 7 is a circuit diagram illustrating in detail the modulator shown in FIG. 6.

8 is a waveform diagram illustrating a response characteristic of a liquid crystal display according to an exemplary embodiment of the present invention.

<Description of Symbols for Main Parts of Drawings>

61: Timing Controller 62: Modulator

63: data driver 64: gate driver

65: data line 66: gate line

67 liquid crystal display panel 73 frame memory

74: lookup table

SW: switch

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 to reduce image quality deterioration when the response characteristics of liquid crystals are accelerated.

The liquid crystal display device displays an image by adjusting light transmittance of liquid crystal cells according to a video signal.

Among the liquid crystal display devices, an active matrix type liquid crystal display device in which switching elements are formed for each liquid crystal cell is advantageous in implementing a moving picture because active control of the switching elements is possible. As a switching element used in an active matrix type liquid crystal display device, a thin film transistor (hereinafter referred to as TFT) is mainly used.                         

As can be seen in Equations 1 and 2, the liquid crystal display has a disadvantage in that the response speed is slow due to the inherent viscosity and elasticity of the liquid crystal.

(gamma)는 액정분자의 회전점도(rotational viscosity)를 각각 의미한다. Where τr is the rising time when voltage is applied to the liquid crystal, Va is the applied voltage, VF is the Freederick Transition Voltage at which the liquid crystal molecules start the tilt motion, and d is the liquid crystal. The cell gap of the cell,

(gamma) means rotational viscosity of liquid crystal molecules, respectively.

Here, τf denotes a falling time during which the liquid crystal is restored to its original position by the elastic restoring force after the voltage applied to the liquid crystal is turned off, and K denotes an elastic modulus inherent to the liquid crystal.

The liquid crystal response speed of the TN mode (Twisted Nematic mode), which has been the most commonly used liquid crystal display device, can vary depending on the physical properties of the liquid crystal material and the cell gap. 20-30 ms. The response speed of the liquid crystal is longer than one frame period (NTSC: 16.67ms). For this reason, as shown in FIG. 1, since the voltage charged in the liquid crystal cell reaches the next voltage before the desired voltage, the motion blurring phenomenon in which the screen is blurred appears in the video.

Referring to FIG. 1, when the data VD changes from one level to another level due to a slow response speed, the liquid crystal display device does not reach a desired luminance because the corresponding display luminance BL does not reach a desired luminance. You won't be able to. As a result, the motion blurring phenomenon appears in the moving image, and the image quality is deteriorated due to the decrease in the contrast ratio.

In order to solve the slow response speed of the liquid crystal display, U.S. Patent No. 5,495,265 and PCT International Publication No. WO 99/05567 use a lookup table to modulate the data depending on whether or not the data is changed (hereinafter, 'high speed driving'). Has been proposed. This high speed drive method modulates data on the same principle as in FIG.

을 크게 하게 된다. 따라서, 고속 구동방법을 이용하는 액정표시소자는 액정의 늦은 응답속도를 데이터값의 변조로 보상하여 동영상에서 모션 블러링 현상을 완화시킨다. Referring to FIG. 2, the fast driving method modulates the input data VD into preset modulation data MVD and applies the modulation data MVD to the liquid crystal cell to obtain a desired luminance MBL. This high-speed driving method uses Equation 1 based on whether or not the data changes so as to obtain a desired luminance corresponding to the luminance value of the input data within one frame period.

To make it larger. Therefore, the liquid crystal display device using the high speed driving method compensates for the late response speed of the liquid crystal by modulating the data value to mitigate the motion blur phenomenon in the video.

In other words, the high speed driving method compares data between the previous frame and the current frame, and if there is a change between the data, modulates the data of the current frame with preset modulation data. The high speed driving device in which the high speed driving method is implemented may be implemented as shown in FIG. 3.

Referring to FIG. 3, the high speed drive device includes a frame memory 33 for storing data from the data input line 32 and a lookup table 34 for modulating the data.

The frame memory 33 stores data in units of frames according to the pixel clock and outputs the stored data to supply the previous frame data, that is, the n−1 th frame data Fn−1, to the lookup table 34.

The lookup table 34 compares the n th frame data Fn from the data input line 32 with the n-1 th frame data Fn from the frame memory 33 and modulates the corresponding modulation data ( MRGB) is selected from Table 1 to modulate the data. The modulation data MRGB of Table 1 is stored in a read only memory (ROM).

division 0 One 2 3 4 5 6 7 8 9 10 11 12 13 14 15 0 0 2 3 4 5 6 7 9 10 12 13 14 15 15 15 15 One 0 One 3 4 5 6 7 8 10 12 13 14 15 15 15 15 2 0 0 2 4 5 6 7 8 10 12 13 14 15 15 15 15 3 0 0 One 3 5 6 7 8 10 11 13 14 15 15 15 15 4 0 0 One 3 4 6 7 8 9 11 12 13 14 15 15 15 5 0 0 One 2 3 5 7 8 9 11 12 13 14 15 15 15 6 0 0 One 2 3 4 6 8 9 10 12 13 14 15 15 15 7 0 0 One 2 3 4 5 7 9 10 11 13 14 15 15 15 8 0 0 One 2 3 4 5 6 8 10 11 12 14 15 15 15 9 0 0 One 2 3 4 5 6 7 9 11 12 13 14 15 15 10 0 0 One 2 3 4 5 6 7 8 10 12 13 14 15 15 11 0 0 One 2 3 4 5 6 7 8 9 11 13 14 15 15 12 0 0 One 2 3 4 5 6 7 8 9 10 12 14 15 15 13 0 0 One 2 3 3 4 5 6 7 8 10 11 13 15 15 14 0 0 One 2 3 3 4 5 6 7 8 9 11 12 14 15 15 0 0 0 One 2 3 3 4 5 6 7 8 9 11 13 15

In Table 1, the leftmost column is data of the previous frame Fn-1, and the uppermost row is data of the current frame Fn.

Recently, research has been conducted to adjust the response speed of liquid crystals in a time shorter than one frame period in response to consumer demand. However, when the response speed of the liquid crystal is adjusted to reach the target luminance TBL in a time shorter than one frame period as shown in FIG. 4, the liquid crystal molecules become excessively responsive beyond the target luminance TBL, resulting in the liquid crystal response characteristic. Overshoot 41 will appear. In the next data, the response time of the liquid crystal molecules becomes longer due to the transient response in the previous data. The transient response of the liquid crystal and the delay of the recovery time cause the deterioration of image quality. As an example, when some images are scrolled to the right as shown in FIG. 5, a band of complementary color 50 appears heavily at the left end of the moving image due to the transient response of the liquid crystal and the delay of the return time. .

Accordingly, an object of the present invention is to provide a liquid crystal display device and a method of driving the same, which reduce image quality degradation caused by transient response and return delay of liquid crystal when data is modulated to reach a target luminance within less than one frame period. In providing.

In order to achieve the above object, the liquid crystal display according to the present invention generates the first modulation data according to the first source data corresponding to the first period, and the second source data corresponding to the second period immediately after the first period. And a data modulator for generating second modulated data according to the first modulated data. And a liquid crystal display panel displaying data modulated by the first modulated data in the first period and data modulated by the second modulated data in the second period.

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A method of driving a liquid crystal display according to the present invention includes generating first modulated data according to first source data corresponding to a first period; Generating second modulated data according to second source data and the first modulated data corresponding to a second period immediately after the first period; In the second period of time, displaying data modulated by the second modulated data.

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Other objects and features of the present invention in addition to the above objects will become apparent from the description of the embodiments with reference to the accompanying drawings.

Hereinafter, exemplary embodiments of the present invention will be described with reference to FIGS. 4 to 8.

Referring to FIG. 4, in the liquid crystal display according to the present invention, a liquid crystal display panel 67 in which a data line 65 and a gate line 66 cross each other and a TFT for driving the liquid crystal cell Clc is formed at an intersection thereof. And a data driver 63 for supplying data to the data line 65 of the liquid crystal display panel 67 and a gate driver 64 for supplying scan pulses to the gate line 66 of the liquid crystal display panel 67. And the data modulator 62 for modulating the source data SRGB to the preset modulation data MRGB, the data driver 63 and the gate driver 64, and the source data to the data modulator 62. A timing controller 61 for supplying (SRGB) is provided.
The liquid crystal display panel 67 includes liquid crystals injected between two glass substrates, and includes data lines 65 and gate lines 66 formed to be orthogonal to each other on the lower glass substrate of the pair of glass substrates. The TFT formed at the intersection of the data lines 65 and the gate lines 66 causes the liquid crystal cell Clc to supply data from the data lines 65 in response to a scan pulse from the gate line 66. do. For this purpose, the gate electrode of the TFT is connected to the gate line 66 and the source electrode is connected to the data line 65. The drain electrode of the TFT is connected to the pixel electrode of the liquid crystal cell Clc. In this case, the liquid crystal cell Clc equivalently displays the liquid crystal affected by the electric field between the pixel electrode and the common electrode.
In addition, a storage capacitor Cst is formed on the lower glass substrate of the liquid crystal display panel 67 to maintain the voltage of the liquid crystal cell Clc. The storage capacitor Cst includes one side connected to the pixel electrode to be connected in parallel with the liquid crystal cell Clc. In particular, the storage capacitor Cst may be formed between the liquid crystal cell Clc and the front gate line 66. It may be formed between (Clc) and a separate common line.

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The data driver 63 applies a signal to each data line 65 in each horizontal period in response to the data control signal DDC from the timing controller 61. The data driver 63 stores the shift register, the register for temporarily storing the modulation data MRGB from the timing controller 61, and the data for each line in response to the clock signal from the shift register. A latch for outputting data at the same time, a digital / analog converter for selecting an analog positive / negative gamma compensation voltage corresponding to the digital data value from the latch, and a data line to which a positive / negative gamma compensation voltage is supplied. A multiplexer for selecting 65) and an output buffer connected between the multiplexer and the data line. The data driver 63 receives modulated data MRGB from the timing controller 61 and receives the modulated data MRGB from the data lines 65 of the liquid crystal display panel 67 under the control of the timing controller 61. To feed.

The gate driver 64 shifts the shift register which sequentially generates scan pulses in response to the gate control signal GDC from the timing controller 61, and the swing width of the scan pulses to a level suitable for driving the liquid crystal cell Clc. Level shifter, output buffer, and so on. The gate driver 64 turns on the TFTs connected to the gate line 66 by supplying a scan pulse to the gate line 66 to supply the pixel voltage of the data, that is, the analog gamma compensation voltage. The liquid crystal cells Clc of one horizontal line are selected. The pixel voltage of the data generated from the data driver 63 is supplied to the liquid crystal cell Clc of one horizontal line selected by the scan pulse by being synchronized with the scan pulse.
In summary, the gate driver 64 sequentially supplies scan pulses to the gate lines 66 in one vertical period required to scan all of the liquid crystal cells Clc, and the gates to which the scan pulses are applied. The TFTs connected to the line 66 are turned on to supply the signal of the data line 65 to the pixel electrode of the liquid crystal cell Clc. The data driver 63 supplies each data signal, that is, a pixel voltage, to the entire data line 65 every one horizontal period for scanning liquid crystal cells corresponding to one gate line in one vertical period. The pixel voltage at this time is modulated data MRGB modulated by the data modulator 62 in response to the source data SRBG supplied from the timing controller 61.

The timing controller 61 controls the gate control signal GDC and the data driver 63 to control the gate driver 64 using the vertical / horizontal synchronization signals V and H and the pixel clock CLK. Generate a data control signal DDC. The timing controller 61 samples the digital source data SRGB in accordance with the pixel clock CLK and supplies the source data SRGB to the data modulator 62.

The modulated data MRGB listed in the lookup table in the data modulator 62 is set to data that reaches the target luminance within a time period less than one frame period, for example, 8 ms, at the time of data change. The data modulator 62 selects the modulation data MRGB using the first input source data SRGB and the next input source data SRGB as the address of the lookup table, and modulates in the previous frame for subsequent data. The modulated data MRGB is selected from the lookup table using the modulated data MRGB and the source data SRGB of the current frame as addresses of the lookup table. The modulated data MRGB selected by the data modulator 62 satisfies the following Equations 3 to 5 below.

Fn (SRGB) <Fn-1 (MRGB, SRGB) ---> Fn (MRGB) <Fn (SRGB)

Fn (SRGB) = Fn-1 (MRGB, SRGB) ---> Fn (MRGB) = Fn (SRGB)

Fn (SRGB)> Fn-1 (MRGB, SRGB) ---> Fn (MRGB)> Fn (SRGB)

As can be seen from Equations 3 to 5, the modulation data MRGB is the source data SRGB of the current frame Fn than the modulation data MRGB and source data SRGB of the previous frame Fn-1. Is larger than the source data SRGB of the current frame Fn, while the current frame Fn is larger than the modulation data MRGB and source data SRGB of the previous frame Fn-1. If the source data SRGB is smaller than the source data of the current frame Fn, it is set smaller. The modulation data MRGB is the source data of the current frame Fn if the modulation data MRGB and the source data SRGB of the previous frame Fn-1 and the source data SRGB of the current frame Fn are the same. It is set to the same value as (SRGB).

7 shows data modulator 62 in detail.

Referring to FIGS. 7 and 8, the data modulator 62 according to the present invention includes a frame memory 73 for storing source data SRGB and modulated data MRGB, which are first input from the data input line 72. And modulated data set in advance using the switch SW for selecting data stored in the frame memory 73, the data from the frame memory 73 and the source data SRGB from the input line 72 as addresses. And a lookup table 74 for outputting MRGB).

The frame memory 73 stores the first input source data SRGB and the modulation data RGB selected by the lookup table 74 in units of frames and supplies the stored data to the lookup table 74.

The switch SW supplies the first input source data F1 (SRGB) to the frame memory 73 under the control of the timing controller 61, and thereafter, the switch SW supplies the horizontal data to each other by the lookup table 74 which will be described later. The modulated data Fi (MRGB) (i is a natural number of 2 or more) selected according to the source data SRGB corresponding to the period is supplied to the frame memory 73.

The lookup table 74 has a modulation data MRGB set in advance according to the conditions of Equations 3 to 5 using the source data MRGB from the data input line 72 and the data MRGB from the frame memory 73 as addresses. Select).

On the other hand, the data modulated by the lookup table 74 is the most significant 4 bit data in order to reduce the memory capacity. Therefore, the modulated data MRGB supplied to the data driver 63 is data obtained by adding the least significant 4 bits of data of the source data SRGB and the most significant 4 bits of data of the modulated data MRGB.
The data modulator 62 described above is summarized as follows.
The data modulator 62 according to the embodiment of the present invention receives the source data SRGB from the timing controller 61, generates modulation data MRGB corresponding to the source data SRGB, and sends the result to the timing controller 61. Is authorized. At this time, the source data SRGB corresponds to each horizontal period.
As illustrated in FIG. 7, the data modulator 62 is connected to the timing controller 61 to receive data input lines 72 for receiving source data SRGB corresponding to each horizontal period from the timing controller 61. A switch SW for selecting any one of the data input line 72 and an output end of the lookup table 74 to be described later, a frame memory 73 for storing data selected by the switch, and source data corresponding to each horizontal period. And a lookup table 74 for generating modulation data MRGB corresponding to (SRGB) and previous modulation data corresponding to the horizontal period immediately before it.
Here, in the case of a horizontal period (hereinafter, referred to as an initial horizontal period) of a frame including a driving start point, the switch SW does not have modulation data generated before the initial horizontal period, and thus the source data F1 corresponding to the initial horizontal period On the contrary, in the case of the horizontal period Fn except the initial horizontal period, the modulation data Fn-1 (generated according to the source data Fn-1 (SRGB) corresponding to the immediately preceding horizontal period) is selected. MRGB)).
The lookup table 74 includes setting values such that the target luminance corresponding to all the source data SRGB can be displayed by the liquid crystal cell within a time shorter than one frame period (for example, 8 ms). The lookup table 74 receives the source data Fn (SRGB) corresponding to the current horizontal period from the data input line 72 and modulates the data Fn-1 corresponding to the immediately preceding horizontal period from the frame memory 73. (MRGB)), the current source data Fn (SRGB) and the previous modulation data Fn-1 (MRGB) as addresses, and the modulation data Fn (MRGB) corresponding to the current horizontal period among the set values. Select)).
Although not separately illustrated in FIG. 7, the data modulator 62 uses the current modulated data Fn (MRGB) output from the lookup table 74 to input the current source data Fn (inputted from the data input line 72). SRGB)) can be corrected and the corrected data can be output to the data driver 63. For example, the output value of the data modulator 62 may be determined as the sum of the current modulated data Fn (MRGB) and the current source data Fn (SRGB).
Alternatively, the data modulator 62 outputs both the current modulated data Fn (MRGB) and the current source data Fn (SRGB) to the data driver 63, and the data driver 63 outputs the current modulated data Fn ( MRGB)) to correct the current source data Fn (SRGB).
On the other hand, in order to reduce the memory capacity, the data modulator 62 may input and modulate only the most significant 4-bit data of the source data SRGB.

As shown in FIG. 8, the liquid crystal display according to the present invention includes a data modulator 62, and currently inputs data previously modulated from modulated data preset to reach the target luminance TBL at a time smaller than one frame period. The overshoot of the liquid crystal response characteristics is reduced by compensating the transient response of the liquid crystal with previous modulation data in comparison with the source data. Therefore, in the liquid crystal display device of the present invention, even if the response characteristic of the liquid crystal is adjusted in a time smaller than one frame period, the complementary color distortion which appears in the scroll direction when the image is scrolled does not appear.

As described above, the memory driving method and apparatus of the liquid crystal display device according to the present invention, when modulating the data with the preset modulation data to reach the target luminance in a time less than one frame period, the next input data of the modulation data In comparison, by modulating the source data, it is possible to compensate for the transient response of the liquid crystal to the previous modulated data, thereby reducing the deterioration of image quality caused by the return delay.

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

Claims (8)

Generating first modulated data according to the first source data corresponding to the first period, and generating second modulated data according to the second source data and the first modulated data corresponding to the second period immediately after the first period. A data modulator; And a liquid crystal display panel for displaying data modulated by the first modulated data in the first period and displaying data modulated by the second modulated data in the second period. The method of claim 1, The data modulator, A data input line into which source data corresponding to each period is input; In the case of the third period corresponding to the frame including the initial driving, the third source data corresponding to the third period is selected, and in the remaining periods except the third period, the period is generated corresponding to the previous period of each period. A switch for selecting modulation data; A frame memory for storing data selected by the switch; And a look-up table for generating modulation data corresponding to each period according to source data corresponding to each period input to the data input line and data stored in the frame memory. delete The method of claim 2, The lookup table includes modulation data set to a value indicating a target luminance in the liquid crystal display panel at a time smaller than one frame, corresponding to each source data. In response to the second period, the second modulation data is selected from among the set modulation data by using the first modulation data and the second source data selected by the switch and stored in the frame memory as addresses; And corresponding to the third period of time, the third modulation data is selected from among the set modulation data by using the third source data selected by the switch as an address. Generating first modulated data according to the first source data corresponding to the first period of time; Generating second modulated data according to second source data and the first modulated data corresponding to a second period immediately after the first period; And displaying data modulated by the second modulated data in the second period. The method of claim 5, The generating of the second modulated data may include: And selecting the second modulated data from among values at which the liquid crystal cell reaches a target luminance for a time smaller than one frame period by using the first modulated data and the second source data as addresses. Method of driving display device. The method of claim 6, When the first period corresponds to a frame including initial driving, generating the first modulated data may include: And selecting the first modulated data from among values at which the liquid crystal cell reaches a target luminance for a time smaller than the one frame period, using the first source data as an address. Method of driving the device. The method of claim 5, Before displaying the data modulated by the second modulated data, And adding the second modulated data and the second source data to generate the modulated data.

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