Method and apparatus for driving liquid crystal display

A driving apparatus is provided for a for a liquid crystal display. The driving apparatus includes a lamp housing, a plurality of lamps arranged in the lamp housing, and a lamp driver. The lamp driver drives a first set of the plurality of lamps to sequentially turn on and off and substantially simultaneously drives a second set of the lamps to be constantly turned on.

The present invention claims the benefit of Korean Patent Application No. P2002-78378 filed in Korea on Dec. 10, 2002, which is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a driving apparatus and method of driving a liquid crystal display, and more particularly, to a driving apparatus and method of driving a liquid crystal display that improves the brightness of the liquid crystal display in accordance with a back light sequential driving system.

2. Description of the Related Art

The liquid crystal display (LCD), is light weight, thin, and low in power consumption. As a result, LDCs have been increasingly applied in a wide variety of applications including office automation instruments, and audio/video devices. The LCD displays a desired picture on a screen by controlling the transmissivity of light beam in accordance with a video signal applied to a plurality of control switches arranged in a matrix.

The LCD with such a configuration has been replacing the cathode ray tube (CRT) due to the above mentioned light weight and low power consumption. One of the reasons facilitating the increased use of LCDs is technological innovation such as the picture quality improvement of the LCD. Though the cathode ray tube CRT uses an impulse of light emission by the scan of an electron gun, the LCD uses a hold-type of the light emission employing a back light system where a linear lamp (fluorescent lamp) is an illuminating light source. As a result, it is impossible to display a perfect moving picture. In other words, when a moving picture is displayed by the LCD, moving picture contour deterioration occurs due to the hold characteristic, thereby causing deterioration of picture quality.

FIG. 1is a simulation diagram illustrating a mechanism of how a moving picture contour deterioration is generated when the moving picture is displayed on the display device such as LCD having a hold property.FIG. 1(A)illustrates that a white image being moved in an direction of arrow A is displayed on part of a black background of the LCD.FIG. 1(B)is an enlarged diagram of the boundary area of the black/white images.FIG. 1(C)is a diagram explaining the cause of occurrence of the moving picture contour deterioration.FIG. 1(D)is an enlarged diagram representing the moving picture contour deterioration. Wherein each of squares shown inFIG. 1represents a pixel. Further, the moving picture contour deterioration is indicated as “a blurring” or as “a moving picture blurring” inFIG. 1.

As illustrated inFIG. 1(C), where one row of the black/white boundary area ofFIG. 1(B)is displayed in a time series, a line of sight moves along arrow B, which is slantingly drawn from top left to bottom right, as a displayed picture is moved in an arrow A direction. The brightness of a pixel is sustained or held while a display of one frame is moving. Because the brightness is represented by the integration of the brightness of pixel, the moving picture contour deterioration occurs as illustrated inFIG. 1(D).

On the other hand, such moving picture contour deterioration does not occur in the impulse type of cathode ray tube “CRT”. More specifically,FIG. 2is the same simulation diagram asFIG. 1(C)where the moving picture is displayed in the CRT not having a hold property. Because the pixel is not displayed while the picture moves between frames, even though the line of sight moves along the arrow B in accordance with the movement of a display picture in an arrow A direction, there occurs no moving picture contour deterioration. In other words, in the impulse type of CRT, black data is displayed between an initial frame and a new frame, so the display picture gets visually vivid due to the black data.

Accordingly, as illustrated inFIGS. 1(C) and 2, an observer's perceived image in the moving picture is vividly displayed in the CRT. As compared with this, the displayed picture becomes blurred in the LCD because of the hold property of liquid crystal in moving pictures. The difference of such a perceived image results from the integration effect of image that temporarily lasts in the eye pursuing the movement. Accordingly, even though the response speed of the LCD is fast, the observer sees a blurred screen owing to a discord between eye's movement and a static image of each frame.

Accordingly, there is a back light sequential driving system for an LDC employing a direct back light where a plurality of lamps are arranged horizontally to prevent the moving picture contour deterioration. The LCD according to the back light sequential driving system turns on/off a plurality of lamps in synchronization with the start time of the scan signal of the display picture, and in addition, when the brightness signals of the same level are applied, the display brightness of the LCD makes the time integration value of the brightness value equalized between each frames, thereby preventing the moving picture contour deterioration from occurring when displaying the moving picture similar to that of an impulse type light emission such as the CRT.

Referring toFIGS. 3 and 4, the driving apparatus for the liquid crystal display employing a back light sequential driving system includes an LCD panel2having TFTs at intersection areas where data lines and gate lines cross, a data driver4for supplying data to the data lines of the LCD panel2, a gate driver6for supplying gate pulses to the gate lines of the LCD panel2, a back light unit10for providing a light beam to the LCD panel2by sequentially driving a plurality of lamps30, a lamp driver12for controlling the back light unit10, and a timing controller8for controlling the data driver4and the gate driver6as well as driving the lamp driver12.

A back light unit10, as shown inFIG. 4, includes a plurality of lamps30, a lamp housing22enclosing the plurality of lamps30, and a diffusion plate20which covers the front of the lamp housing22. The plurality of lamps30is sequentially driven in response to the control of the lamp driver12. The lamp housing22encloses the plurality of lamps30and directs the light beam from the plurality of lamps30toward the diffusion plate20using a reflection surface24. The diffusion plate20allows the light radiated from a plurality of lamps30to proceed to the liquid crystal display panel2with a wide angle of incidence. The diffusion plate20uses a member coated on both sides with films of transparent resin to achieve optical diffusion.

In the LCD panel2, a liquid crystal is injected between two glass substrates. The TFTs are formed at the intersection areas of the data lines and the gate lines of the liquid crystal display panel2, thereby providing the liquid crystal cell with the data on the data line in response to a scanning pulse from the gate driver6. The source electrode of the TFT is connected to the data line, the drain electrode is connected to a pixel electrode of the liquid crystal cell, and the gate electrode of the TFT is connected to the gate line. The liquid crystal display panel2is stacked on the diffusion plate20of the back light unit10.

The timing controller8rearranges the digital video data supplied from a digital video card (not shown) by red (R), green (G), and blue (B), respectively. The data (R, G, B) rearranged by the timing controller8is supplied to the data driver4. Further, the timing controller8generates a data control signal and a gate control signal using the horizontal/vertical synchronization signal (H/V) input to itself. The data control signal including a dot clock (Dclk), a source shift clock (SSC), a source enable signal (SOE), and a polarity inversion signal (POL) is supplied to the data driver4. The gate control signal including a gate start pulse (GSP), a gate shift clock (GSC), and a gate output enable (GOE) is supplied to the gate driver6. Further, the timing controller8controls the lamp driver12so that the back light unit10may sequentially be driven at a point of time when the data is completely supplied to the liquid crystal cell.

The data driver4latches the sampled data line by line after sampling the data in accordance with data control signal from the timing controller8, and then converts the latched data into an analog gamma voltage from a gamma voltage supplying part (not shown). The gate driver6includes a shift register for generating the gate pulse sequentially in response to the gate start pulse (GSP) among the gate control signal from the timing controller8, and a level shifter for shifting the voltage of the gate pulse to the voltage level suitable for driving the liquid crystal cell. The lamp driver12drives a plurality of lamps30of the back light unit10sequentially in response to the lamp driving control signal from the timing controller8. More specifically, the lamp driver12drives a plurality of lamps30sequentially after the data voltage is supplied to the liquid crystal cell completely.

In the driving apparatus of the liquid crystal display device as described, a plurality of lamps30are driven sequentially when a plurality of gate lines are driven during one frame as shown inFIG. 5. More specifically, when the gate pulse is supplied to the gate lines of at least GL—1 to GL—1+M among N gate lines and the data voltage is completely supplied through the data lines to the liquid crystal cell, the first lamp30is turned off after being turned on. Further, when the gate pulse is supplied to the gate lines of at least GL—(1+M)+1 to GL—1+2M among the N gate lines and the data voltage is supplied through the data lines to the liquid crystal cell, the second lamp is turned off after being turned-on.

Here, the computation of the brightness is explained according to the above described scanning back light driving method. In the first place, the brightness of hold-type back light driving method constantly turning on back light is defined as equation 1. Here, it is assumed that the brightness of 1 frame is 1 in case that one lamp is turned on.Brightness(Hold⁢-⁢Type)=⁢(1+1+1+⋯+1)/1⁢⁢Frame⁢⁢Time=⁢n/1⁢⁢Frame[Equation⁢⁢1]

Hereby, the brightness of the scanning back light driving method is reduced in inverse proportion to the number of the lamps by contrast with the hold-type back light driving method as illustrated in equation 2.Brightness(Scanning⁢⁢Type)=⁢(1/n+1/n+1/n+⋯+1/n)/1⁢⁢Frame=⁢1/1⁢⁢Frame[Equation⁢⁢2]

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a driving apparatus and method of liquid crystal display that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.

An object of the present invention is to provide a driving apparatus and method of liquid crystal display for improving the brightness of liquid crystal display according to a back light sequential driving system.

To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, the driving apparatus and method of liquid crystal display includes a driving apparatus for a liquid crystal display comprises a lamp housing; a plurality of lamps arranged in the lamp housing; and a lamp driver to drive a first set of the plurality of lamps to sequentially turn on and off and to substantially simultaneously drive a second set of the lamps to be constantly turned on.

In another aspect, a driving method for a liquid crystal display having a plurality of lamps disposed in a lamp housing comprises the steps of sequentially turning on and off a first set of the plurality of lamps during one frame; and turning on a second set of the plurality of lamps simultaneously with the step of sequentially turning on and off the first set of lamps, the second set of lamps being turned on constantly during the one frame.

In another aspect, a liquid crystal display comprises a liquid crystal display panel; a lamp housing having a plurality of lamps arranged therein to provide light to the liquid crystal panel; and a lamp driver to drive a first set of the plurality of lamps to sequentially turn on and off and to substantially simultaneously drive a second set of the lamps to be constantly turned on.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring toFIGS. 6 and 7, a driving apparatus of a liquid crystal display employs a back light sequential driving scheme according to an embodiment of the present invention. The driving apparatus includes a liquid crystal display panel102in which data lines and gate lines intersect with TFTs at the intersections, a data driver104for supplying data to the data lines of the liquid crystal display panel102, a gate driver106for supplying gate pulses to the gate lines of the liquid crystal display panel102, a back light unit110for providing light to the liquid crystal display panel102using a plurality of first and second lamps130,132, first and second lamp drivers112,114for controlling the first and the second lamps130,132in the back light unit110, and a timing controller108for driving the first and the second lamp drivers112,114as well as for controlling the data driver104and the gate driver106.

The back light unit110in a driving apparatus of a liquid crystal display according to a configuration as shown inFIG. 7includes the first and the second lamps130,132arranged in the first and the second rows, a lamp housing122enclosing the lamps130,132, and a diffusion plate120covering the front of the lamp housing122.

The lamps130,132are driven in response to the control of each of the first and the second lamp drivers112,114arranged in the first and the second row as a cold cathode fluorescent tube (CCFL) or a light emitting diode. More specifically, the first lamps130arranged in the first row are driven sequentially by the first lamp driver112, and the second lamps132arranged in the second row are constantly turned on by the second lamp driver114.

The lamp housing122encloses the first and the second lamps130,132and makes the light beam progress from the first and the second lamps130,132to the diffusion plate120through a reflection surface124. The diffusion plate120enables the light from the first and the second lamps130,132to pass to the liquid crystal display panel102with a wide angle of incidence. The diffusion plate120may use a member coated on both sides with films of transparent resin.

In the liquid crystal display panel102, liquid crystal is injected between two glass substrates. The TFTs are formed at the intersection areas of the data lines and the gate lines of the liquid crystal display panel102for supplying data from the data lines to a liquid crystal cell in response to a scanning pulse from the gate driver106. The source electrode of each TFT is connected to a respective gate line, the drain electrode of each TFT is connected to a respective pixel electrode of the liquid crystal cell, and the gate electrode of each TFT is connected to a respective gate line. The liquid crystal display panel102is stacked on the diffusion plate120of the back light unit110.

The timing controller108rearranges the digital video data supplied from a digital video card (not shown) by red (R), green (G), and blue (B), respectively. The data (R,G,B) rearranged by the timing controller108is supplied to the data driver104. Further, the timing controller108generates data control signals and gate control signals in use of the horizontal/vertical synchronization signals (H, V) provided to itself. The data control signal is supplied to the data driver104including a dot clock (Dclk), a source shift clock (SSC), a source enable signal (SOE), and a polarity inversion signal (POL). The gate control signal is supplied to the gate driver106including a gate start pulse (GSP), a gate shift clock (GSC), and a gate output enable (GOE). Further, at the moment that data is completely supplied to the liquid crystal cell, the timing controller108drives the back light unit110sequentially and, at the same time, controls the first and the second lamp drivers112,114to be driven.

After the data driver104samples the data according to the data control signal from the timing controller108, it latches the sampled data line by line and converts the latched data to the analog gamma voltage from gamma voltage supplying part (not shown). The gate driver106includes a shift register generating gate pulses sequentially and a level shifter shifting a gate pulse voltage to the voltage level suitable for driving the liquid crystal in response to the gate start pulse (GSP) among the gate control signals from the timing controller108.

The first lamp driver112sequentially drives the first lamps130arranged in the first row of the back light unit110in response to the lamp driving control signal from the timing controller108. More specifically; after the data voltage is completely supplied to the liquid crystal cell, the first lamp driver112turns on/off the first lamps130sequentially. In response to the lamp driving control signal from the timing controller108, the second lamp driver114drives the second lamps132arranged in the second row of the back light unit110, and turns the second lamps132constantly on. At this time, the current supplied to the first lamp130arranged in the first row is larger than the current supplied to the second lamps132arranged in the second row.

In the driving apparatus of the liquid crystal display according to the embodiment of the present invention as shown inFIG. 8, the first lamps130are turned on/off sequentially when a plurality of gate lines are driven within one frame. In other words, when the gate pulse is supplied to at least gate lines GL—1 to GL—1+M among N gate lines and when data voltage is supplied to the data lines, the first lamp among a plurality of first lamps130arranged in the first row is turned off after being turned-on. At this time, the lamps132arranged in the second row are turned on and maintain the state of being turned-on. Further, when the gate pulse is supplied to at least gate lines GL—(1+M)+1 to GL—1+2M among the N gate lines and when data voltage is supplied to the data lines, the second lamp among the first lamps130arranged in the first row is turned off after being turned-on. Hereby, in respect to the liquid crystal display panel102the light beam from the first lamps130arranged in the first row driven sequentially, and the light beam from the second lamps132arranged in the second row constantly driven in a state of being turned-on are irradiated to the liquid crystal display panel102.

Accordingly, the driving apparatus of the liquid crystal display of the first embodiment of the present invention does not use all the lamps130,132all for being turned-on/off. In particular, the first lamps130—corresponding to the some of the lamps such as half of the lamps—use a scanning back light driving method, the second lamps132constantly maintain the state of being turned-on, thereby improving the brightness. More specifically, as described above, the first lamps130arranged in the first row among the first and the second lamps130,132arranged in the first and the second rows in the lamp housing120are driven by the scanning back light driving method keeping on/off, and the plurality of the second lamps132arranged in the second row constantly maintain the state of being turned-on, so the brightness is improved as in the following equation 3.
Brightness=(n+1)/1Frame  [Equation 3]

As described in equation 3, because n (the total number of lamps) is larger than 1, the brightness achieved by the driving apparatus of the liquid crystal display is higher than that of the related art scanning back light driving method.

Alternatively, in the driving apparatus of the liquid crystal display according to the configuration as shown inFIG. 7, the first lamps130arranged in the first row of the lamp housing122are driven so that they may constantly maintain a constant the state of turned-on state, and the plurality of the second lamps132arranged in the second row can be driven by the scanning back light driving method to be turned on/off. As a result, the brightness achieved by the driving apparatus of the liquid crystal display is higher than that of the related art scanning back light driving method.

Because a driving apparatus of a liquid crystal display ofFIG. 9is similar to the driving apparatus of the liquid crystal display according to the configuration as shown inFIG. 7except for the arrangement structure of the first and the second lamps230,232arranged in a lamp housing222, the explanation about each component will be omitted.

In the driving apparatus ofFIG. 9, the first and the second lamps230,232are arranged zigzag in the lamp housing222. More specifically, the second lamps232arranged in the second row are each disposed between corresponding ones of the first lamps230, arranged in the first row. A diffusion plate220is stacked on the lamp housing222, and a liquid crystal panel202is stacked on the diffusion plate220. Among these, the first lamps230arranged in the first row are driven by the scanning back light driving method turned on/off sequentially, and the second lamps232arranged in the second row is driven so that they constantly maintain a turned-on state. At this time, the current supplied to the first lamps230arranged in the first row is larger than that supplied to the second lamps232arranged in the second row. Further, the brightness is higher than that of the related scanning back light driving method.

Alternatively, in the driving apparatus of the liquid crystal display according to the configuration as illustrated inFIG. 9, the first lamps230arranged in the second row in the lamp housing222can be driven so that they may constantly maintain a turned-on state, and the plurality of the second lamps232arranged in the second row can be driven by the scanning back light driving method to be turned on/off. As described above, the brightness achieved by the driving apparatus of the liquid crystal display is higher than that of the related art scanning back light driving method.

Because a driving apparatus of a liquid crystal display ofFIG. 10is similar to the driving apparatus of the liquid crystal display according to the configuration as shown inFIG. 7, except for the arrangement structure of the first and the second lamps330,332arranged in a lamp housing322, the explanation about each component will be omitted.

In the driving apparatus ofFIG. 10, the first lamps330are arranged in the first row of the lamp housing322and the second lamps332arranged in the second row are overlapped with the first lamps330of the odd-numbered lamps of the first lamps330arranged in the first row. A diffusion plate320is stacked on the lamp housing322, and a liquid crystal panel302is stacked above the diffusion plate320. The first lamps330arranged in the first row are sequentially driven by the scanning back light driving method turned to be on/off, and the second lamps332arranged in the second row are driven to constantly maintain a turned-on state. At this time, the current supplied to the first lamps330arranged in the first row is larger than that supplied to the second lamps332arranged in the second row. Further, the brightness is higher than that of the related art scanning back light driving method.

Alternatively, in the driving apparatus of the liquid crystal display according to the configuration as shown inFIG. 10, the first lamps330arranged in the second row of the lamp housing322are driven so that they may constantly maintain a turned-on state, and the plurality of the second lamps332arranged in the second row can be driven by the scanning back light driving method to be turned on/off. As described above, the brightness of the driving apparatus of the liquid crystal display is higher than that of the related art scanning back light driving method.

On the other hand, a driving apparatus of a liquid crystal display according to another embodiment, in which a plurality of lamps is arranged in more than two rows in the lamp housing, can drive the lamps as dividing the driving method of the lamps of each row into the scanning back light driving method and the hold-type back light driving method.

Referring toFIGS. 11 and 12, a driving apparatus of a liquid crystal display may include a plurality of lamps430,432arranged in the first row in a lamp housing422. A diffusion plate420is stacked on the lamp housing422, and a liquid crystal display panel402is stacked above the diffusion plate420. The driving apparatus ofFIG. 11has odd-numbered lamps430of the plurality of lamps430,432driven by the scanning back light driving method to be turned on/off as shown inFIG. 12and has even-numbered lamps432driven by the hold-type back light driving method to be turned on constantly. Further, the brightness is higher than that of the related art scanning back light driving method as shown in equation 4.Brightness=⁢(1/n+1+1/n+1+⋯+1/n+1)/1⁢⁢Frame=⁢(n/2+1/2)/1⁢⁢Frame[Equation⁢⁢4]

Alternatively, in the driving apparatus of the liquid crystal display according to the configuration as shown inFIG. 11, the odd-numbered lamps430of the plurality of lamps430,432arranged in the lamp housing422may constantly maintain a turned-on state, and even-numbered lamps432may be driven by scanning back light driving method to be turned on/off. On the contrary, the driving apparatus makes odd-numbered lamps430among the plurality of lamps430,432driven by the scanning back light driving method to be turned on/off and drives so that the even-numbered lamps432may maintain a constant turned-on state. As described above, the brightness is higher than that of the related art scanning back light driving method. The even-numbered lamps432driven by the scanning back light driving method can be driven sequentially upon scanning driving or the some of the lamps can be driven sequentially. As described above, the brightness achieved by the driving apparatus is higher than that of the related scanning back light driving method.

As described above, the driving apparatus and the method of the liquid crystal display according to the present invention arranges a plurality of lamps in at least two groupings in the lamp housing, wherein the some of these lamps are driven by the scanning driving method to sequentially turn on/off and the rest are driven by the hold-type driving method to constantly maintain a turned-on state. Here, the groupings may correspond to respective rows. Alternatively, the lamps may be arranged in one row, wherein odd-numbered (or even-numbered) lamps are driven by the scanning driving method to be turned on/off sequentially, and even-numbered (or odd-numbered) lamps are driven by the hold-type driving method to maintain a constant turned-on state. Hereby, the present invention can improve the brightness and reduce motion blurring.