KR20040002294A - Method and Apparatus For Driving Liquid Crystal Display - Google Patents

Abstract

PURPOSE: An LCD driving device and a method thereof are provided to reduce the memory capacitance of a lookup table by inputting upper 7bit source data to the lookup table and setting 8bit modulation data and improve the screen quality by high speed driving. CONSTITUTION: An LCD driving device includes a timing controller having a control signal generating part for generating gate and data control signals, and a lookup table comparing source data of current and previous frames(Fn,Fn-1) by 7bit unit and outputting modulation data of 8bit. The lookup table compares upper 7 bits of the current frame with lower 7bits of the previous frame and selects 8bit modulation data corresponding to the comparison result. The modulation data is set to a value possibly generating undershoot but not overshoot.

Description

Method and apparatus for driving liquid crystal display device {Method and Apparatus For Driving Liquid Crystal Display}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device, and more particularly, to a method and apparatus for driving a liquid crystal display device to reduce the capacity of a data modulation memory and to improve image quality.

In general, a liquid crystal display (LCD) displays an image by adjusting light transmittance of liquid crystal cells according to a video signal. An active matrix liquid crystal display device in which switching elements are formed for each liquid crystal cell is suitable for displaying moving images. As a switching element used in an active matrix 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.

Where τ _r is the rising time when voltage is applied to the liquid crystal, Va is the applied voltage, and V _F is the Freederick Transition Voltage at which the liquid crystal molecules begin their inclined motion, d Is the cell gap of the liquid crystal cell, (gamma) means rotational viscosity of liquid crystal molecules, respectively.

Here, τ _f 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 the elastic modulus inherent to the liquid crystal.

The liquid crystal response speed of the TN mode may vary depending on the physical properties of the liquid crystal material, the cell gap, and the like, but usually has a rising time of 20-80 ms and a polling time of 20-30 ms. Since the response speed of the liquid crystal is longer than one frame period (NTSC: 16.67 ms) of the video, the screen is blurred in the video because the voltage charged in the liquid crystal cell proceeds to the next frame as shown in FIG. 1. Motion blurring phenomenon appears.

Referring to FIG. 1, a conventional liquid crystal display device does not reach a desired display luminance BL when the data VD changes from one level to another due to a slow response speed when a video is implemented. It will not be able to express color and brightness. As a result, the motion blurring phenomenon appears in the moving picture, and the display 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 driving method modulates data in the same principle as in FIG. 2.

Referring to FIG. 2, the conventional high speed driving method modulates the input data VD 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 is changed to obtain a desired luminance corresponding to the luminance value of the input data within one frame period. To make it larger. Accordingly, the liquid crystal display device using the high speed driving method compensates the late response speed of the liquid crystal by modulating the data value, thereby alleviating the motion blurring phenomenon in the moving image, thereby displaying an image with a desired color and luminance.

In other words, the fast driving method compares the most significant bit data MSB of each of the previous frame Fn-1 and the current frame Fn, and if there is a change between the most significant bit data MSB, the corresponding modulation data in the lookup table. Select (Mdata) to modulate as shown in FIG. This high speed driving method modulates only the upper few bits in order to reduce the capacity burden of the memory in hardware implementation. The high speed drive device implemented as described above is illustrated in FIG. 4.

Referring to FIG. 4, the conventional high speed drive device is commonly connected to the frame memory 43 connected to the upper bit bus line 42 and the output terminals of the upper bit bus line 42 and the frame memory 43. The lookup table 44 is provided.

The frame memory 43 stores the most significant bit data MSB for one frame period and supplies the stored data to the lookup table 44. Here, the most significant bit data MSB is set to the upper 4 bits among the 8 bit source data RGB Data In.

The lookup table 44 includes the upper bit data MSB of the current frame Fn input from the upper bit bus line 42 and the upper bit data MSB of the previous frame Fn-1 input from the frame memory 43. ) And the modulation data (Mdata) corresponding to the comparison result are selected. The modulated data Mdata is added to the bit data LSB from the lower bit bus line 41 and supplied to the liquid crystal display. Table 1 shows the most significant ^{4 bit (2 4, 2 5} , 2 6, 2 7) and the top ^{4 bit (2 4, 2 5} , 2 6, 2 7) of the current frame (Fn) of a previous frame (Fn-1) An example of a lookup table 44 for comparing the? And selecting the modulation data Mdata corresponding to the result of the comparison is shown.

division 0 16 32 48 64 80 96 112 128 144 160 176 192 208 224 240 0 0 32 48 64 80 96 112 144 160 192 208 224 240 240 240 240 16 0 16 48 64 80 96 112 128 160 192 208 224 240 240 240 240 32 0 0 32 64 80 96 112 128 160 192 208 224 240 240 240 240 48 0 0 16 48 80 96 112 128 160 176 208 224 240 240 240 240 64 0 0 16 48 64 96 112 128 144 176 192 208 224 240 240 240 80 0 0 16 32 48 80 112 128 144 176 192 208 224 240 240 240 96 0 0 16 32 48 64 96 128 144 160 192 208 224 240 240 240 112 0 0 16 32 48 64 80 112 144 160 176 208 224 240 240 240 128 0 0 16 32 48 64 80 96 128 160 176 192 224 240 240 240 144 0 0 16 32 48 64 80 96 112 144 176 192 208 224 240 240 160 0 0 16 32 48 64 80 96 112 128 160 192 208 224 240 240 176 0 0 16 32 48 64 80 96 112 128 144 176 208 224 240 240 192 0 0 16 32 48 64 80 96 112 128 144 160 192 224 240 240 208 0 0 16 32 48 48 64 80 96 112 128 160 176 208 240 240 224 0 0 16 32 48 48 64 80 96 112 128 144 176 192 224 240 240 0 0 0 16 32 48 48 64 80 96 112 128 144 176 208 240

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

The reason for modulating only the 4-bit upper bit data MSB is to reduce the memory capacity of the lookup table 44.

However, when the lookup table 44 adopts a 4-bit comparison method to reduce memory capacity, there is a problem in that the quality between the gray scales is not linear and the leap occurs.

In order to reduce such deterioration of image quality, the data width of the modulation data listed in the lookup table 44 should be large enough, and the input source data should be compared in full bit, for example, in units of 8 bits.

Table 2 shows an example of a lookup table in which modulation data (Mdata) is 8 bits and source data is compared in 8 bit full bit units.

In this case, when the lookup table is compared in full bit 8 bit unit and the modulation data (Mdata) pre-stored in the lookup table is 8 bit, the gray level is changed linearly, and thus the image quality is excellent. There is an increasing disadvantage. For example, if the lookup table is compared in 8 bit units and the modulation data Mdata is 8 bits, the memory capacity of the lookup table is increased to 65536 × 8 = 524,000 bits. Here, the first term '65536' on the left side is 8 bits of the source data product (256 × 256) in each of the previous frame (Fn-1) and the current frame (Fn), and the second term '8' on the left side is a lookup table. It is the data width (8 bits) of the modulation data listed in (44). In addition, for color realization, considering red, green, and blue (RGB), the memory capacity of the lookup table reaches 65536 x 8 x 3 = 1,572,000 bits. Therefore, if the lookup table adopts an 8-bit comparison method for high-speed driving, as the memory capacity increases, the manufacturing cost increases and the chip size increases.

Accordingly, an object of the present invention is to provide a method and apparatus for driving a liquid crystal display device, which reduces the capacity of a data modulation memory and improves image quality.

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 conventional high speed driving method.

3 is a diagram illustrating an example of a conventional high speed driving method in 8 bit data.

4 is a block diagram showing a conventional high speed drive device.

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

FIG. 6 is a block diagram illustrating in detail the timing controller shown in FIG. 5.

FIG. 7 is a diagram illustrating a modulation data setting method of the lookup table illustrated in FIG. 6.

<Description of Symbols for Main Parts of Drawings>

41: Lower Bit Busline 42: Upper Bit Busline

43,58,59: frame memory 44,62: lookup table

51: timing controller 53: data driver

54 gate driver 55 data line

56 gate line 57 liquid crystal panel

60: input line 61: control signal generator

In order to achieve the above object, a method of driving a liquid crystal display according to the present invention includes a first under in a first data band including first modulated data set larger than a data value of a current frame in response to an increase in a data value. Setting chute data; Setting second undershoot data within a second data band including second modulated data set smaller than a data value of a current frame in response to a decrease in the data value; receiving source data of n bits, where n is a positive integer; Comparing the source data of the previous frame and the current frame in units of n-k (where k is a positive integer smaller than n) and modulating the source data using the undershoot data.

The driving method of the liquid crystal display according to the present invention further includes modulating the source data with data of the current frame if the data value is the same between the previous frame and the current frame.

The method of driving the liquid crystal display according to the present invention comprises the steps of: modulating the source data using the first undershoot data when the source data value of the current frame is increased from the previous frame as a result of comparing the source data of the previous frame and the current frame; ; And modulating the source data by using the second undershoot data when the source data value of the current frame decreases as a result of comparing the source data of the previous frame and the current frame.

A driving device of a liquid crystal display according to the present invention comprises: an input line for inputting source data of n bits, where n is a positive integer; The first undershoot data selected in the first data band including the first modulated data larger than the data value of the current frame corresponding to the increase in the data value and the smaller value than the data value of the current frame in response to the decrease of the data value. 2 List the second undershoot data selected in the modulation data band, compare the source data of the previous frame with the current frame in units of nk (where k is a positive integer less than n) and use the undershoot data to obtain the source data. And a modulator that modulates.

In the driving apparatus of the liquid crystal display according to the present invention, the modulator modulates the source data with the data of the current frame if the data value is the same between the previous frame and the current frame.

A driving apparatus of a liquid crystal display according to the present invention comprises: a first frame memory for delaying data from an input line for one frame period and for supplying delayed data to a modulator; And a second frame memory for delaying data from the first frame memory for one frame period and for supplying the delayed data to the modulator.

In the driving apparatus of the liquid crystal display according to the present invention, the modulator modulates the source data using the first undershoot data when the source data value of the current frame is increased from the previous frame as a result of comparing the source data of the previous frame and the current frame. To; As a result of comparing the source data of the previous frame and the current frame, if the source data value of the current frame is reduced from the previous frame, the source data is modulated using the second undershoot data.

According to an exemplary embodiment of the present invention, a driving apparatus of a liquid crystal display device includes: a liquid crystal display panel in which a plurality of data lines and a plurality of gate lines intersect, and a liquid crystal cell is formed in a pixel region between the data line and the gate line to display an image; A data driver for supplying modulation data from a modulator to data lines of the liquid crystal display panel; A gate driver for supplying a scan signal to a gate line of the liquid crystal display panel; A timing controller for controlling the data driver and the gate driver is further provided.

In the driving apparatus of the liquid crystal display according to the present invention, the modulator is a look-up table built in the timing controller.

In the method and apparatus for driving a liquid crystal display according to the present invention, the first undershoot data is set to a minimum value within a first data band.

In the method and apparatus for driving a liquid crystal display according to the present invention, the second undershoot data is set to a maximum value within a second data band.

In the method and apparatus for driving a liquid crystal display according to the present invention, n is '8' and k is '1'.

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. 5 to 7.

Referring to FIG. 5, a driving device of a liquid crystal display according to the present invention includes a liquid crystal panel in which a data line 55 and a gate line 56 cross each other and a TFT for driving the liquid crystal cell Clc is formed at an intersection thereof. 57, a data driver 53 for supplying data to the data line 55 of the liquid crystal panel 57, and a gate driver 54 for supplying scan pulses to the gate line 56 of the liquid crystal panel 57. ) And a timing controller 51 for modulating the data through comparison of the upper 7 bits from the 8-bit source data and generating timing control signals DDC and GDC, the input line 60 and the timing controller 51. First and second frame memories 58 and 59 connected between the plurality of transistors.

In the liquid crystal panel 57, liquid crystal is injected between two glass substrates, and the data lines 55 and the gate lines 56 are orthogonal to each other on the lower glass substrate. The TFT formed at the intersection of the data lines 55 and the gate lines 56 supplies the data on the data lines 55 to the liquid crystal cell Clc in response to a scan pulse from the gate line 56. . For this purpose, the gate electrode of the TFT is connected to the gate line 56 and the source electrode is connected to the data line 55. The drain electrode of the TFT is connected to the pixel electrode of the liquid crystal cell Clc.

The data driver 53 stores the data by one line in response to a shift register for sampling the dot clock of the timing control signal DDC, a register for temporarily storing the data, and a clock signal from the shift register. For outputting the data at the same time; an analog / digital converter for selecting a positive / negative gamma voltage corresponding to a digital data value from the latch; and a data line 55 for outputting data from the analog / digital converter. It consists of a multiplexer for selecting and an output buffer connected between the multiplexer and the data line. The data driver 53 receives the modulated data Mdata of red (R), green (G), and blue (B) colors modulated by the timing controller 51 to control the gate from the timing controller 51. The modulated data Mdata is supplied to the data lines 55 of the liquid crystal panel 57 in response to the signal DDC.

The gate driver 54 shifts a shift register that sequentially generates scan pulses in response to the gate control signal GDC from the timing controller 51, and shifts the voltage of the scan pulses to a level suitable for driving the liquid crystal cell Clc. Level shifter and the like.

The timing controller 51 compares the source data Fn and Fn-1 input from the first and second frame memories 58 and 59 in the upper 7 bit units and compares the modulation data Mdata corresponding to the comparison result. Will be chosen. The modulated data Mdata selected by the timing controller 51 is input to the data driver 53. In addition, the timing controller 51 controls the gate control signal GDC and the data driver 53 for controlling the gate driver 54 using the vertical / horizontal synchronization signals V and H and the main clock MCLK. A data control signal DDC is generated.

The first frame memory 58 stores data from the input line 60 for one frame period and supplies the data RGB of the current frame Fn stored to the second frame memory 59 and the timing controller 51. do.

The second frame memory 59 stores data from the first frame memory 58 for one frame period, and supplies the data RGB of the previous frame Fn-1 to the timing controller 51.

On the other hand, between the input line 60 and the frame memory 58, an interface circuit adopting an interface method such as Low Voltage Differential Signaling (LVDS), Transition Minimized Differential Signaling (TMDS), RSDS, etc. Can be installed. Furthermore, the first frame input and output ends of the first and the second frame memory 59 of the memory 58, the bit conversion circuit, or discard the least significant bit (2 ⁰⁾ in the source data of 8 bit takes a top 7 bit 7 bit Bus lines may be installed.

6 shows the timing controller 51 in detail.

Referring to FIG. 6, the timing controller 51 according to the present invention includes a control signal generator 61 for generating a gate control signal GDC and a data control signal DDC, a current frame Fn, and a previous frame ( A lookup table 62 for comparing the source data of Fn-1) in units of 7 bits and outputting modulation data of 8 bits is provided.

The control signal generator 61 receives the gate start pulse GSP, the gate shift clock GSC, and the gate output enable GOE using the vertical / horizontal synchronization signals V and H and the main clock MCLK. Generate a gate control signal (GDC) including the data enable signal (DE), the source shift clock (SSC), the source start pulse (SSP), the polarity control signal (POL), and the source output enable signal (SOE). Generate a data control signal DDC.

The lookup table 62 shows the upper 7 bits (2 ⁷ , 2 ⁶ , 2 ⁵ , 2 ⁴ , 2 ³ , 2 ² , 2 ¹ ) of the current frame (Fn) and the lower 7 bits (2 ⁷ ) of the previous frame (Fn). , 2 ⁶ , 2 ⁵ , 2 ⁴ , 2 ³ , 2 ² , 2 ¹ ), and 8-bit modulation data corresponding to the comparison result are selected.

When the data input to the timing controller 51 represents '200' and '201' as a binary number, 11001000 ₂ and 11001001 ₂ are the upper 7 bits (2 ⁷ , 2 ⁶ , 2 ⁵ , 2 ⁴ , 2 ³ , The values of 2 ² , 2 ¹ are the same and only the least significant bit (2 ⁰ ) is different. Therefore, when the data supplied to the input line 60 is '200' and '201', 1100100 is input to the lookup table 62.

The modulation data listed in the lookup table 62 satisfies the high speed driving conditions as shown in the following relational expressions ① to ③.

VDn <VDn-1 ---> MVDn <VDn -------- ①

VDn = VDn-1 ---> MVDn = VDn, -------- ②

VDn> VDn-1 ---> MVDn> VDn. -------- ③

In (1) to (3), VDn-1 represents the data voltage of the previous frame, VDn represents the data voltage of the current frame, and MVDn represents the modulated data voltage, respectively.

In the case of the relation ③, the overshoot occurs electrically and optically when the modulation data Mdata is higher than the optimum value, and in the case of the relation ①, the undershoot (electrically / optically) when the modulation data Mdata is lower than the optimum value. Undershoot occurs. In the overshoot, since the brightness of the image is rapidly increased, the degradation of image quality that the observer feels subjectively is severe, whereas the undershoot hardly decreases the image quality that the observer feels subjectively. Therefore, it is preferable that the modulation data Mdata listed in the lookup table 62 is set to a value where only an undershoot can appear without overshooting. To this end, when the modulation data (Mdata) listed in the lookup table 62 is divided into three bands of the relations (1) to (3), four modulation data (Mdata) is generated in the modulation data band satisfying the relation (1) as shown in FIG. Each adjacent small band is set to a maximum value. In addition, each of the small bands adjacent to the four modulation data Mdata in the modulation data band satisfying the relation (3) is set to a minimum value. In FIG. 7, the modulation band Mdata is set to a value equal to the value of the data RGB currently input in the data band satisfying the relation (2).

Table 3 and 4 show an example of the lookup table 62. Table 3 sets the modulation data (Mdata) in the lookup table of Table 2 by converting the source data into 7 bits and generating an undershoot of a modulation data band satisfying relations (1) and (3). Table 4 is a reconstruction of the lookup table of Table 3 by taking any one when the source data in Table 3 is the same.

Comparing Tables 2 and 3, the conventional small bands '106,108,106,107' satisfying the relation 1 in the lookup table 62 are converted to undershoot values, i.e., the maximum values 108,108,108,108. Further, in the lookup table 62, the conventional small bands '144, 145, 144 and 145' which satisfy the relation 3 are converted to undershoot values, i.e., the minimum values (144, 144, 144 and 144).

The memory capacity of the lookup table 62 according to the present invention is 16,384 × 8 = 131,072 bits, and considering the red, green, and blue colors (RGB), the memory capacity of the lookup table is 16,384 × 8 × 3 = 393,216 bits. Compared by 8 bit unit, memory capacity is greatly reduced compared to lookup table with 8 bit modulated data. Here, the first term '16, 384 'on the left side is the source data product (128 × 128) of 7 bits in the previous frame (Fn-1) and the current frame (Fn), and the second term' 8 'on the left side is the modulation data. Data width (8 bits).

As described above, the method and apparatus for driving the liquid crystal display according to the present invention reduce the memory capacity of the lookup table by inputting the upper 7 bits of the source data into the lookup table and setting the modulation data of 8 bits, and the high speed driving method. To improve the picture quality. Furthermore, the driving device of the liquid crystal display according to the present invention integrates the lookup table 52 into the timing controller 51 to simplify the circuit configuration by integrating the timing controller 51 and the lookup table 52 into a single chip. In addition, the number of bus lines formed on the driving printed circuit board (PCB) can be reduced, and high frequency noise and electromagnetic interference (EMI) can be reduced.

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. For example, the data modulator may be implemented in other forms, such as a program and a microprocessor for executing the lookup table. In addition, the technical idea according to the present invention may be applied to all fields requiring data modulation, for example, digital flat panel displays other than telecommunications, optical media, and liquid crystal displays. In addition, although the embodiment has been described as a method of selecting a 7-bit comparison method and 8-bit modulation data by assuming 8 bits of data input through the input line, the case where the data input through the input line is 6 bits is described. You may compare the lookup table with 5 bits and set the modulation data to 6 bits. 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 (15)

Setting first undershoot data within a first data band including first modulated data set larger than a data value of a current frame in response to an increase in the data value; Setting second undershoot data within a second data band including second modulated data set smaller than a data value of the current frame in response to a decrease in a data value; receiving source data of n bits, where n is a positive integer; comparing the source data of the previous frame and the current frame in units of nk (where k is a positive integer smaller than n) and modulating the source data using the undershoot data. Method of driving display device. The method of claim 1, And the first undershoot data is set to a minimum value in the first data band. The method of claim 1, And the second undershoot data is set to a maximum value in the second data band. The method of claim 1, And modulating the source data with data of the current frame if the data value is the same between the previous frame and the current frame. The method of claim 1, Modulating the source data using the first undershoot data when the source data value of the current frame is increased as a result of comparing the source data of the previous frame and the current frame; And modulating the source data by using the second undershoot data when the source data value of the current frame is lower than the previous frame as a result of comparing the source data of the previous frame and the current frame. A method of driving a liquid crystal display device. The method of claim 1, N is '8' and k is '1'. an input line for inputting source data of n bits, wherein n is a positive integer; Smaller than the data value of the current frame in response to a decrease in the selected first undershoot data and the data value within the first data band containing the first modulated data that is larger than the data value of the current frame in response to an increase in the data value. List the selected second undershoot data within the second modulation data band, compare the source data of the previous frame and the current frame in units of nk (where k is a positive integer less than n) and compare the undershoot data. And a modulator for modulating the source data by using the modulator. The method of claim 7, wherein And the first undershoot data is set to a minimum value in the first data band. The method of claim 7, wherein And the second undershoot data is set to a maximum value in the second data band. The method of claim 7, wherein And the modulator modulates the source data with data of the current frame if the data value is the same between the previous frame and the current frame. The method of claim 7, wherein A first frame memory for delaying data from the input line for one frame period and for supplying the delayed data to the modulator; And a second frame memory which delays the data from the first frame memory for one frame period and supplies the delayed data to the modulator. The method of claim 7, wherein The modulator modulates the source data using the first undershoot data when the source data value of the current frame is increased as a result of comparing the source data of the previous frame and the current frame; And comparing the source data of the previous frame with the source data of the current frame to reduce the source data value of the current frame to modulate the source data using the second undershoot data. Drive. The method of claim 7, wherein A liquid crystal display panel in which a plurality of data lines and a plurality of gate lines cross each other and a liquid crystal cell is formed in a pixel region between the data line and the gate line to display an image; A data driver for supplying modulation data from the modulator to a data line of the liquid crystal display panel; A gate driver for supplying a scan signal to a gate line of the liquid crystal display panel; And a timing controller for controlling the data driver and the gate driver. The method of claim 7, wherein And the modulator is a look-up table built in the timing controller. The method of claim 7, wherein Wherein n is '8' and k is '1'.