Abstract:
A liquid crystal display device includes a display unit having matrix type pixels defined by gate and data lines crossing with each other, a data driver to supply a data voltage to be supplied to the data lines via output lines, the output lines being less in number than the data lines, a plurality of demultiplexers, each including a plurality of switching devices having a gate terminal, source terminal and a drain terminal, wherein the gate terminals are supplied with a plurality of control signals, the source terminals are commonly connected to the corresponding output line, and the drain terminals are individually connected to one side of the data lines, respectively, a data line check unit activated to supply a test data voltage to the other side of the data lines when the data driver is inactive, a plurality of signal input lines individually connected to the gate terminals, respectively, an input terminal supplied with a cutoff signal to be inputted to the signal input lines to turn off the switching devices, and a switching unit electrically connecting/disconnecting the input terminal to/from the signal input lines according to an external control signal.

Description:
This application claims the benefit of the Korean Patent Application No. P2005-0047650 filed on Jun. 3, 2005, which is hereby incorporated by reference. 
     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 driving method thereof. 
     2. Discussion of the Related Art 
     Generally, a liquid crystal display (LCD) device displays a picture corresponding to a video signal (i.e., “data voltage”) using a display unit having a plurality of pixels defined by gate and data lines crossing with each other. Each pixel of the display unit consists of a liquid crystal cell adjusting light transmittance according to a corresponding data voltage. A thin film transistor (TFT) acts as a switching device to supply a data voltage from a data line to the liquid crystal cell. The LCD device also includes a gate driver for driving the gate lines and a data driver for driving the data lines. In a liquid crystal panel where the TFT is formed of polysilicon having high electric charge mobility, the gate and data drivers are built in the liquid crystal panel. In such a case, a demultiplexer unit is provided between the data driver unit and the display unit. The demultiplexer unit connects a plurality of data lines to one output line of the data driver, thereby reducing a required number of drive ICs (integrated circuit) needed to configure the data driver. 
     An LCD device provided with a demultiplexer unit according to a related art is explained with reference to the attached drawings as follows.  FIG. 1  shows a block diagram of an LCD device according to a related art. 
     As shown in  FIG. 1 , an LCD device according to the related art includes of a display unit  111  on which m-gate lines GL 1  to GLm and n-data lines DL 1  to DLn perpendicularly cross each other to form (m×n) pixels arranged in a matrix form. A TFT is provided at each intersection of the gate and data lines. A gate driver  101  provides a scan pulse voltage SP to the gate lines GL 1  to GLm and a data driver  102  supplies data voltages VD 1  to VDk to the data lines DL 1  to DLn of the display unit  111 . A demultiplexer unit  105  is connected between the display unit  111  and the data driver  102 , and a timing controller  106  controls the gate driver  101 , the data driver  102 , and the demultiplexer unit  105 . 
     The timing controller  106  generates a plurality of control signals to control the drive timing of the gate and data drivers  101  and  102  and aligns pixel data to be applied to the data driver  102 . Further, the timing controller  106  generates a plurality of control signals to control the demultiplexer unit  105 . 
     The data driver  102  has a number of output lines OL 1  to OLk connected to the output pins (not shown) of the data driver  102 . The number of output pins (k) is equal to the number of output lines OL 1  to OLk. However, the number of output lines OL 1  to OLk connected between the data driver  102  and the demultiplexer unit  105  is smaller than a number of the data lines DL 1  to DLn. The demultiplexer unit  105  is explained in detail as follows. 
       FIG. 2  shows a detailed schematic diagram of the demultiplexer unit  105  shown in  FIG. 1 .  FIG. 3  shows a diagram of drive waveforms of a first demultiplexer DEMUX 1  shown in  FIG. 2  during a random horizontal sync interval. 
     As shown in  FIG. 2 , the demultiplexer unit  105  includes k-demultiplexers DMUX 1  to DEMUXk connected between the data driver unit  102  and n-data lines DL 1  to DLn of the display unit  111 . Each of the demultiplexers DEMUX 1  to DEMUXk includes first to third switching devices SW 1  to SW 3  connected in parallel to one output line OLk and to three of the data lines DL 1  to DLn, respectively. The first to third switching devices SW 1  to SW 3  are turned on at different times in one horizontal period by first to third control signals C 1  to C 3  supplied from the timing controller  106 , respectively. The gate driver  101  sequentially supplies a scan pulse voltage SP to m-gate lines GL 1  to GLm during one frame. As shown in  FIG. 3 , a gate high voltage VGH, which is a high logic voltage of the scan pulse voltage SP, is maintained to drive a corresponding gate line during one horizontal sync period. In this case, the gate high voltage VGH is set to a voltage level that is greater than a threshold voltage of the TFT. Conversely, a gate low voltage VGL is a low logic voltage of the scan pulse voltage SP set as an off-voltage of the TFT. 
     During a horizontal sync period Hi of driving a selected gate line, the data driver  102  sequentially supplies k-data voltages VD 1  to VDk to k-output lines OL 1  to OLk connected to the k-demultiplexers DEMUX 1  to DEMUXk, respectively. The k-data voltages VD 1  to VDk supplied to the k-demultiplexers DEMUX 1  to DEMUXk are synchronized with the first to third control signals C 1  to C 3  from the timing controller  106  to supply three data voltages from each of the k-data voltages VD 1  to VDk to the three data lines connected to each of the demultiplexers DEMUX 1  to DEMUXk to supply data signals to the n-data lines DL 1  to DLn. 
     More specifically, in each of the k-demultiplexers DEMUX 1  to DEMUXk, a gate electrode of the first switching device SW 1  is connected to a signal input line IL of the first control signal C 1 . Likewise, a gate electrode of the second switching device SW 2  is connected to a signal input line IL of the second control signal C 2 , and a gate electrode of the third switching device SW 3  is connected to a signal input line IL of the third control signal C 3 . Hence, when the first to third control signals C 1  to C 3 , as shown in  FIG. 3 , are sequentially shifted to a high state in one horizontal sync period Hi, the first to third switching devices SW 1  to SW 3  of each of the demultiplexers DEMUX 1  to DEMUXk are driven in sequence from of the first switching device SW 1  to the third switching device SW 3 . The data driver  102  sequentially outputs the corresponding data voltages VD 1  to VDk to correspond to the drive sequence of the first to third switching devices SW 1  to SW 3 . As a result, the first demultiplexer DEMUX 1 , as shown in  FIG. 3 , sequentially supplies the data voltage for R (red) to the first data line DL 1  via the first switching device SW 1 , the data voltage for G (green) to the second data line DL 2  via the second switching device SW 2 , and the data voltage for B (blue) to the third data line DL 3  via the third switching device SW 3 . 
     In the LCD device of the related art, the display unit  111 , the gate driver  101 , data driver  102 , and each of the demultiplexers DEMUX 1  to DEMUXk to drive the display unit  111  are built into an LCD panel  100 . In particular, the data driver  102  of a chip-type is mounted on the LCD panel  100  (e.g., chip on glass “COG”). The timing controller  106  is provided external to the LCD panel  100 . 
     To check whether the image according to the data voltages VD 1  to VDk is correctly displayed on each of the pixels, the related art liquid crystal display device further includes a gate line check unit of checking a presence or absence of errors on the gate lines GL 1  to GLm and a data line check unit of checking a presence absence of error on the data lines DL 1  to DLn. A liquid crystal display device having a gate line check unit and a data line check unit according to the related art is explained in detail as follows. 
       FIG. 4  shows a block diagram of an LCD device having a gate line check unit and a data line check unit according to the related art. As shown in  FIG. 4 , an LCD device according to the related art includes of a display unit  111  on which m-gate lines GL 1  to GLm and n-data lines DL 1  to DLn perpendicularly cross each other to form (m×n) pixels arranged in a matrix form. A TFT is provided at each intersection of the gate and data lines. A gate driver  101  provides a scan pulse voltage SP to the gate lines GL 1  to GLm and a data driver (not shown) supplies data voltages VD 1  to VDk to the data lines DL 1  to DLn of the display unit  111 . A plurality of demultiplexers DEMUX 1  to DEMUXk is connected between the display unit  111  and the data driver (not shown). A timing controller (not shown) controls the gate driver  101 , the data driver (not shown), and the demultiplexers DEMUX 1  and DEMUXk. A gate line check unit  403  checks for a presence or absence of errors on the gate lines GL 1  to GLm by supplying a test scan pulse voltage VT to the gate lines GL 1  to GLm of the display unit  111 . A data line check unit  404  checks for a presence or absence of errors on the data lines DL 1  to DLn by supplying test data voltages VTR (red), VTG (green), and VTB (blue) to the data lines DL 1  to DLn of the display unit  111 . In particular, each of the demultiplexers DEMUX 1  to DEMUXk has the same configuration of the demultiplexer shown in  FIG. 2 . 
     The gate line check unit  403  is connected to one end of each of the gate lines GL 1  to GLm and the gate driver  101  is connected to the other end of each of the gate lines GL 1  to GLm. Similary, the data line check unit  404  is connected to one end of each of the data lines DL 1  to DLn and the data driver  102  is connected to the other end of each of the data lines DL 1  to DLn via the demultiplexers DEMUX 1  to DEMUXk, respectively. 
     The gate line check unit  403  includes m-fourth switching devices SW 4  supplying the test scan pulse voltage VT to the m-gate lines GL 1  to GLm in response to a fourth control signal C 4 . Namely, one of the fourth switching devices SW 4  is connected to one gate line. In particular, gate terminals of the fourth switching devices SW 4  are connected in parallel to be supplied with the fourth control signal C 4  in common. Drain terminals are individually connected to the gate lines GL 1  to GLm, respectively, and source terminals are connected in parallel to be supplied with the test scan pulse voltage VT in common. 
     The data line check unit  404  includes n-fifth switching devices SW 5  supplying the test data voltages VTR, VTG, and VTB to the data lines DL 1  to DLn in response to a fifth control signal C 5 . In particular, gate terminals of the fifth switching devices SW 5  are connected parallel to each other to be supplied with the fifth control signal C 5  in common. Drain terminals are individually connected to the data lines DL 1  to DLn, respectively, and source terminals are supplied with one of the test data voltages VTR, VTG, and VTB. 
     As previously described, the gate and data line check units  403  and  404  are provided to check whether the gate and data lines GL 1  to GLm and DL 1  to DLn are in proper operating conditions. When the gate and data line check units  403  and  404  are activated, the gate and data drivers  101  and  102  are deactivated. Specifically, the gate and data line check units  403  and  404  are to temporarily operate the gate and data lines GL 1  to GLm and DL 1  to DLn before the LCD device is activated by the gate and data drivers  101  and  102  for normal operation. Hence, while the gate and data line check units  403  and  404  are in operation, the gate and data drivers  101  and  102  are disabled. Conversely, during normal operations, the gate and data line check units  403  and  404  are disabled while the gate and data drivers  101  and  102  and the timing controller (not shown) are activated. 
     The display unit  111 , the gate driver  101 , the data driver (not shown), the gate line check unit  403 , the data line check unit  404 , and the demultiplexers DEMUX 1  to DEMUXk are built into the LCD panel (not shown). Similar to the description above in relation to  FIGS. 1 and 3 , the data driver is mounted on the LCD panel in the form of a chip. The timing controller is provided external the LCD panel. 
     In the related art, the process of checking the gate and data lines GL 1  to GLm and DL 1  to DLn is carried out prior to loading the data driver  102  and the timing controller  106 . Hence, the gate and data drivers  101  and  102  are disabled in the checking process. First, by applying the fourth control signal C 4  to the gate line check unit  403 , the fourth switching devices SW 4  of the gate line check unit  403  are turned on. Once the fourth switching devices SW 4  are turned on, each of the fourth switching devices SW 4  outputs the test scan pulse voltages VT to the gate lines GL 1  to GLm, respectively. Hence, all of the TFTs connected to the gate lines GL 1  to GLm become active. 
     Subsequently, by applying the fifth control signal C 5  to the data line check unit  404 , the fifth switching devices SW 5  of the data line check unit  404  are turned on. Once the fifth switching devices SW 5  are turned on, each of the fifth switching devices SW 5  outputs one of the test data voltages VTR, VTG, and VTB to the data lines DL 1  to DLn. In particular, test R data voltages VTR are supplied to every third data line starting with the first data line DL 1 , i.e., the first data line DL 1 , the fourth data line DL 4 , to the (n−2)th data line DLn−2. Similarly, the test G data voltages VTG are supplied to every third data line starting with the second data line DL 2 , i.e., the second data line DL 2 , the fifth data line DL 5 , to the (n−1)th data line DLn−1. Likewise, the test B data voltages VTB are supplied to every third data line starting with the third data line DL 3 , i.e., the third data line DL 3 , the sixth data line DL 6 , to the nth data line DLn. The test data voltages VTG, VTG, and VTB supplied to the data lines DL 1  to DLn are supplied to liquid crystal cells of the pixels via the TFTs turned on by the gate line check unit  403 . 
     In this way, all of the pixels can be tested to display different images according to the test data voltages VTR, VTG, and VTB. In doing so, the success/failure of the gate and data lines GL 1  to GLm and DL 1  to DLn, i.e., proper connection/disconnection, can be confirmed by checking the abnormality of the picture displayed on the display unit  111 . For instance, absence of images horizontally along a certain gate line indicates that the pixels connected to that gate line are not operating. Likewise, absence of images vertically along a certain data line indicates that the pixels connected to that data line are not operating. Moreover, if a specific pixel fails to display an image, such a condition indicates that the TFT connected to that particular pixel is malfunctioning. 
     In performing the above-explained test process, the first to third switching devices SW 1  to SW 3  connected to each of the demultiplexers DEMUX 1  to DEMUXk need to be prevented from becoming active. If the first to third switching devices SW 1  to SW 3  are turned on, the active switches SW 1  to SW 3  create a circuit path between the data lines connected thereto, thereby short-circuiting the data lines DL 1  to DLn. In such a case, the test R, G, B data voltages VTR, VTG, and VTB supplied to the data lines DL 1  to DLn via the data line check unit  404  become mixed, thereby preventing proper testing of the pixels. 
     To prevent the first to third switching devices SW 1  to SW 3  in each of the demultiplexers DEMUX 1  to DEMUXk from becoming active during the testing process, a cutoff signal VOFF is supplied to each of the signal input lines IL connected to the gate terminals of the first to third switching devices SW 1  to SW 3  to maintain their off-states. The cutoff signal VOFF is supplied from an external source by an operator via input terminals  411 . The input terminal  411  is connected to one end of each of the signal input lines IL. Because one input terminal is connected to one input line IL, many input terminals  411  are needed to satisfy a large-scale display device with higher resolution. 
     As the display device becomes larger in scale to achieve higher resolution, the number of the data lines DL 1  to DLn increases accordingly. In other words, as the number of the data lines DL 1  to DLn increases, the number of the switching devices in the demultiplexers DEMUX 1  to DEMUXk increases. As the number of the switching devices increases, the corresponding number of the input terminals  411  increases as well. Since the input terminals  411  are formed on the LCD panel  100 , an area for accommodating the input terminals  411  increases in size to accommodate the increased number of input terminals  411 . Hence, the increasing number of the input terminals  411  contravenes the effort to reduce the size of the LCD panel. Moreover, because the fourth control signal C 4 , the test scan pulse voltage VT, the fifth control signal C 5 , and the test data voltages VTR, VTG, and VTB are all provided from an external source, additional input terminals (not shown in the drawing) needed for inputting these signals and voltages also contribute to the size reduction problem. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention is directed to a liquid crystal display device and driving method thereof that substantially obviate one or more problems due to limitations and disadvantages of the related art. 
     An object of the present invention is to provide an LCD device with reduced the number of input terminals. 
     Another object of the present invention is to provide an LCD device with reduced panel size. 
     To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, a liquid crystal display device includes a display unit having matrix type pixels defined by gate and data lines crossing with each other, a data driver to supply a data voltage to be supplied to the data lines via output lines, the output lines being less in number than the data lines, a plurality of demultiplexers, each including a plurality of switching devices having a gate terminal, source terminal and a drain terminal, wherein the gate terminals are supplied with a plurality of control signals, the source terminals are commonly connected to the corresponding output line, and the drain terminals are individually connected to one side of the data lines, respectively, a data line check unit activated to supply a test data voltage to the other side of the data lines when the data driver is inactive, a plurality of signal input lines individually connected to the gate terminals, respectively, an input terminal supplied with a cutoff signal to be inputted to the signal input lines to turn off the switching devices, and a switching unit electrically connecting/disconnecting the input terminal to/from the signal input lines according to an external control signal. 
     In another aspect, a liquid crystal display device includes a display unit having matrix type pixels defined by gate and data lines crossing each other, a data driver to supply data voltages to output lines during normal operations, a plurality of demultiplexers to receive the data voltages from data driver via the output lines and to supply the data voltages to the data lines, each of the demultiplexers including a plurality of switching devices having a gate terminal, a source terminal, and a drain terminal, wherein the source terminals of each demultiplexer are commonly connected to the output line corresponding to the demultiplexer, and the drain terminals are individually connected to corresponding ones of the data lines, a plurality of signal input lines individually connected to the gate terminals of the switching devices, an input terminal supplied with a cutoff signal to turn off the switching devices, and a switching unit to electrically connect the input terminal to the signal input lines during testing operations and to electrically disconnect the input terminal from the signal input lines during the normal operations. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention. In the drawings: 
         FIG. 1  is a block diagram of a liquid crystal display (LCD) device according to a related art; 
         FIG. 2  is a detailed circuit diagram of a demultiplexer unit shown in  FIG. 1 ; 
         FIG. 3  is a diagram of drive waveforms of a first demultiplexer shown in  FIG. 2  during a random horizontal sync interval; 
         FIG. 4  is a block diagram of an LCD device having a gate line check unit and a data line check unit according to the related art; 
         FIG. 5  is a diagram of an LCD device according to an exemplary embodiment of the present invention; and 
         FIG. 6  is a detailed circuit diagram of an exemplary switching unit of  FIG. 5 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. 
       FIG. 5  shows a diagram of an LCD device according to an exemplary embodiment of the present invention.  FIG. 6  is a detailed circuit diagram of an exemplary switching unit of  FIG. 5 . As shown in  FIG. 5 , an LCD device according to an exemplary embodiment of the present invention includes a display unit  555  on which (m×n) pixels are arranged in matrix form by m-gate lines GL 1  to GLm and n-data lines DL 1  to DLn perpendicularly crossing each other and a TFT provided at each intersection of the gate and data lines. A gate driver  501  supplies a scan pulse voltage SP to the gate lines GL 1  to GLm and a data driver (not shown) supplies data voltages VD 1  to VDk via output lines OL 1  to OLk to a plurality of demultiplexers DEMUX 1  to DEMUXk. Each of the plurality of demultiplexers DEMUX 1  to DEMUXk includes first to third switching devices SW 1  to SW 3  to sequentially supply the received data voltages VD 1  to VDk from the output lines OL 1  to OLk to the data lines DL 1  to DLn, respectively, where the number of output lines OL 1  to OLk is smaller than the number of the data lines DL 1  to DLn. A timing controller (not shown) controls the gate driver  501 , the data driver (not shown), and the demultiplexers DEMUX 1  and DEMUXk. 
     The LCD device according to the exemplary embodiment of the present invention also includes a gate line check unit  503  to supply a test scan pulse voltage VT to the gate lines GL 1  to GLm and a data line check unit  504  to supply test data voltages VTR, VTG, and VTB to the data lines DL 1  to DLn. A plurality of signal input lines IL supplying a cutoff signal VOFF to turn off the first to third switching devices SW 1  to SW 3  in each of the demultiplexers DEMUX 1  to DEMUXk is connected to one input terminal  511  that receives the cutoff signal VOFF to be supplied to the signal input lines IL via a switching unit  570 . The switching unit  570  electrically connects/disconnects the input terminal  511  to/from the signal input lines IL according to an external sixth control signal C 6 . 
     The gate line check unit  503  is connected to one end of the gate lines GL 1  to GLm, and the gate driver  501  is connected to the other end of the gate lines GL 1  to GLm. During a test process, the gate line check unit  503  applies a test scan pulse voltage VT to the gate lines GL 1  to GLm to drive the gate lines GL 1  to GLm. During normal operations, the gate driver  501  sequentially supplies the scan pulse voltage SP to the gate lines GL 1  to GLm to sequentially drive the gate lines GL 1  to GLm. 
     The data line check unit  504  is connected to one end of the data lines DL 1  to DLn, and the data driver (not shown) is connected to the other end of the data lines DL 1  to DLn via the demultiplexers DEMUX 1  to DEMUXk, respectively. During a test process, the data line check unit  504  applies one of the select test data voltages VTR, VTG, and VTB to the corresponding data lines DL 1  to DLn to drive the respective data lines DL 1  to DLn. During normal operations, the data driver (not shown) applies the data voltages VD 1  to VDk to the data lines DL 1  to DLn to drive the respective data lines DL 1  to DLn. 
     As explained above, the number of output lines OL 1  to OLk connecting the data driver (not shown) to the demultiplexers DEMUX 1  to DEMUXk, respectively, is smaller than that of the data lines DL 1  to DLn. The output lines OL 1  to OLk are connected to output pins (not shown) of the data driver (not shown). The number (k) of the output pins is equal to that (k) of the output lines OL 1  to OLk. 
     Each of the demultiplexers DEMUX 1  to DEMUXk includes first to third switching devices SW 1  to SW 3  connected in parallel to one output line OLk and to three of the data lines DL 1  to DLn, respectively. The first to third switching devices SW 1  to SW 3  are turned on at different times in one horizontal period by first to third control signals C 1  to C 3  supplied from the timing controller (not shown), respectively. The gate driver  501  sequentially supplies a scan pulse voltage SP to m-gate lines GL 1  to GLm for one frame. As shown in  FIG. 3 , a gate high voltage VGH, which is a high logic voltage of the scan pulse voltage SP, is maintained to drive a corresponding gate line during one horizontal sync period. In this case, the gate high voltage VGH is set to a voltage level that is greater than a threshold voltage of the TFT. Conversely, a gate low voltage VGL is a low logic voltage of the scan pulse voltage SP set as an off-voltage of the TFT. 
     During a horizontal sync period Hi of driving a selected gate line, the data driver (not shown) sequentially supplies k-data voltages VD 1  to VDk to k-output lines OL 1  to OLk connected to the k-demultiplexers DEMUX 1  to DEMUXk, respectively. The k-data voltages VD 1  to VDk supplied to the k-demultiplexers DEMUX 1  to DEMUXk are synchronized with the first to third control signals C 1  to C 3  from the timing controller  106  to supply three data voltages from each of the k-data voltages VD 1  to VDk to the three data lines connected to each of the demultiplexers DEMUX 1  to DEMUXk to supply data signals to the n-data lines DL 1  to DLn. 
     More specifically, in each of the k-demultiplexers DEMUX 1  to DEMUXk, a gate electrode of the first switching device SW 1  is connected to a signal input line IL of the first control signal C 1 . Likewise, a gate electrode of the second switching device SW 2  is connected to a signal input line IL of the second control signal C 2 , and a gate electrode of the third switching device SW 3  is connected to a signal input line IL of the third control signal C 3 . Hence, when the first to third control signals C 1  to C 3 , as shown in  FIG. 3 , are sequentially shifted to a high state in one horizontal sync period Hi, the first to third switching devices SW 1  to SW 3  of each of the demultiplexers DEMUX 1  to DEMUXk are driven in sequence from of the first switching device SW 1  to the third switching device SW 3 . The data driver (not shown) sequentially outputs the corresponding data voltages VD 1  to VDk to correspond to the drive sequence of the first to third switching devices SW 1  to SW 3 . As a result, the first demultiplexer DEMUX 1 , as shown in  FIG. 3 , sequentially supplies the data voltage for R (red) to the first data line DL 1  via the first switching device SW 1 , the data voltage for G (green) to the second data line DL 2  via the second switching device SW 2 , and the data voltage for B (blue) to the third data line DL 3  via the third switching device SW 3 . 
     The gate line check unit  503  includes m-fourth switching devices SW 4  supplying the test scan pulse voltage VT to the m-gate lines GL 1  to GLm in response to a fourth control signal C 4 . Namely, one of the fourth switching device SW 4  is connected to one gate line. In particular, gate terminals of the fourth switching devices SW 4  are connected in parallel to be supplied with the fourth control signal C 4  in common. Drain terminals are individually connected to the gate lines GL 1  to GLm, respectively, and source terminals are connected in parallel to be supplied with the test scan pulse voltage VT in common. 
     The data line check unit  504  includes n-fifth switching devices SW 5  supplying the test data voltages VTR, VTG, and VTB to the data lines DL 1  to DLn in response to a fifth control signal C 5 . In particular, gate terminals of the fifth switching devices SW 5  are connected in parallel to be supplied with the fifth control signal C 5  in common. Drain terminals are individually connected to the data lines DL 1  to DLn, respectively, and source terminals are supplied with one of the test data voltages VTR, VTG, and VTB. 
     The switching unit  570 , as shown in detail in  FIG. 6 , includes a plurality of sixth switching devices SW 6 . The number of the sixth switching devices SW 6  is equal to that of the signal input lines IL. Each gate electrode of the sixth switching devices SW 6  is supplied with a sixth control signal C 6  in common. Each drain terminal is individually connected to the corresponding signal input line IL, and each source terminal is connected to the input terminal  511  in common. Hence, a cutoff signal VOFF is supplied to the three signal input lines IL using only one input terminal  511 . As the fourth control signal C 4 , the test scan pulse voltage VT, the fifth control signal C 5 , the test data voltages VTR, VTG, and VTB, and the sixth control signal C 6  are supplied from an external source, additional input terminals (not shown) for inputting these signals and voltages are provided on the LCD panel (not shown). 
     The gate and data line check units  503  and  504  are provided to check whether the gate and data lines GL 1  to GLm and DL 1  to DLn are in proper operating conditions. The switching unit  570  is provided to sustain the turned-off state of the first to third switching devices SW 1  to SW 3  of the demultiplexers DEMUX 1  to DEMUXk during testing to prevent interference between the test data voltages VTR, VTG, and VTB applied to the data lines DL 1  to DLn. When the gate and data line check units  503  and  504  and the switching unit  570  are activated, the gate driver  501  and the data driver (not shown) are deactivated. Moreover, since a timing controller (not shown) is not needed during the check process, the first to third control signals C 1  to C 3  are not supplied to signal input lines IL. 
     Specifically, the gate and data line check units  503  and  504  and the switching unit  570  temporarily operate the gate and data lines GL 1  to GLm and DL 1  to DLn during the test process. Hence, while the gate and data line check units  503  and  504  and the switching unit  570  are active, the gate driver  501  and the data driver (not shown) are not deactivated. Conversely, during normal operations, the gate and data line check units  503  and  504  and the switching unit  570  are deactivated while the gate driver  501 , the data driver (not shown), and the timing controller (not shown) are active. 
     The display unit  555 , the gate driver  501 , the data driver (not shown), the gate line check unit  503 , the data line check unit  504 , and each of the demultiplexers DEMUX 1  to DEMUXk are built into the LCD panel. In particular, the data driver (not shown) is mounted on the LCD panel in a form of chip (i.e., chip on glass “COG”). The timing controller (not shown) is provided external to the LCD panel. 
     To check the above-configured gate and data lines GL 1  to GLm and DL 1  to DLn and pixels of the liquid crystal display device according to the exemplary embodiment of the present invention, the sixth control signal C 6  is supplied to the gate terminals of the sixth switching devices SW 6  in the switching unit  570 . In response, all of the sixth switching devices SW 6  are switched on, thereby supplying the cutoff signal VOFF provided to the input terminal  511  from an external source to the signal input lines IL. Since the gate terminals of the first third switching devices SW 1  to SW 3  are connected to the signal input lines IL, the cutoff signal VOFF supplied to the signal input lines IL by the switching unit  570  maintains the off-state of the first to third switching devices SW 1  to SW 3 . 
     While the first to third switching devices SW 1  to SW 3  are turned off, the fourth control signal C 4  is applied to the gate line check unit  503 . Accordingly, the fourth switching devices SW 4  of the gate line check unit  503  are switched on, thereby supplying the test scan pulse voltage VT to the gate lines GL 1  to GLm. Hence, all of the TFTs connected to the gate lines GL 1  to GLm are activated. 
     Meanwhile, in response to the fifth control signal C 5 , the fifth switching devices SW 5  of the data line check unit  504  supply the test data voltages VTR (test R data voltage), VTG (test G data voltage), and VTB (test B data voltage) to the corresponding data lines DL 1  to DLn. In particular, the test R data voltage VTR is supplied to every third data line starting with the first data line DL 1 , i.e., the first data DL 1 , the fourth data line DL 4 , to the (n−2)th data line DLn−2. Similarly, the test G data voltage VTG is supplied to every third data line starting with the second data line DL 2 , i.e., the second data line DL 2 , the fifth data line DL 5 , to the (n−1)th data line DLn−1. Likewise, the test B data voltage VTB is supplied to every third data line starting with the third data line DL 3 , i.e., the third data line DL 3 , the sixth data line DL 6 , to the nth data line DLn. Accordingly, when the TFTs are switched on by the test scan test voltage VT, the test data voltages VTG, VTG, and VTB are supplied to the data lines DL 1  to DLn. 
     By displaying the test image on the display unit  555  and by checking the abnormality of the image displayed on the display unit  555 , the success/failure of the gate and data lines GL 1  to GLm and DL 1  to DLn, i.e., whether the gate and data lines GL 1  to GLm and DL 1  to DLn are connected or disconnected, can be confirmed. For instance, absence of images horizontally along a certain gate line indicates that the pixels connected to that gate line are not operating. Likewise, absence of images vertically along a certain data line indicates that the pixels connected to that data line are not operating. Moreover, if a specific pixel fails to display an image, such a condition indicates that the TFT connected to that particular pixel is malfunctioning. 
     Accordingly, the exemplary embodiment of the present invention as described above supplies the cutoff signal to all of the signal input lines using only one input terminal regardless of the increasing number of the signal input lines while still providing an effective way to check for proper operation of the pixels. Moreover, while the above-described example describes the checking process before the gate and data drivers are loaded, the LCD panel according to the present invention can be checked for proper operation at any time by deactivating the gate and data drivers and activating the testing units as described above. 
     It will be apparent to those skilled in the art that various modifications and variations can be made in the LCD device of the present invention without departing form the spirit or scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.