Abstract:
A display device includes a display panel including a first and a second non-display area, a main active area, and a sub active area, wherein the active areas each include a matrix of sub-pixels; a data driver in the first non-display area to provide image data to the matrices of sub-pixels; a main gate driver in the second non-display area to provide a corresponding gate signal to each sub-pixel in the main active area; a sub gate driver in the second non-display area to provide a corresponding gate signal to each sub-pixel in the sub active area; an auto-probe test pad in the non-display area for transmitting a first start signal received from an auto-probe signal generating device to one of the main gate driver and the sub gate driver while testing the display panel; and a signal transmission circuit connecting the main gate driver and the sub gate driver.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of Korean Patent Application No. 10-2015-0120226, filed on Aug. 26, 2015, the entire contents of which is incorporated herein by reference for all purposes as if fully set forth herein. 
       BACKGROUND 
       [0002]    Field of the Disclosure 
         [0003]    The present disclosure relates to a display device. 
         [0004]    Discussion of the Related Art 
         [0005]    Due to development of information technologies, demands for a display device connecting a user to information are increasing. Various types of display devices are used, such as an Organic Light Emitting Display (OLED), a Quantum Dot Display (QDD), a Liquid Crystal Display (LCD), and a Plasma Display Panel (PDP). 
         [0006]    Some of the various display devices, for example, the LCD or the OLED, include a display panel which has a plurality of sub-pixels arranged in a matrix form, a driver which outputs a driving signal for driving the display panel, and a power supply which generates power to be supplied to the display panel or the driver. 
         [0007]    For the LCD or the OLED, a display panel is manufactured and then a test process is conducted to test the display panel. In the test process, an auto-probe test is used to test electrical features of the display panel (e.g., a line shortage test and a lighting test). 
         [0008]    The auto-probe test is conducted in a manner that a probe needle is put in contact with an auto-probe test pad (hereinafter, referred to as an “AP pad”) formed on a substrate of the display panel and then an electrical signal is applied. 
         [0009]    As a result, a structure in which a gate driver is formed in a Gate In Panel (GIP) method on a substrate of the display panel such that a main gate driver and a sub gate driver are able to be driven individually. If the gate driver has the aforementioned structure, an AP pad and a start signal line (hereinafter, referred to as a “AP line”) have to be formed to apply an electrical signal to the main gate driver and the sub gate driver, respectively. 
         [0010]    However, if the AP pad and the AP line are formed on a substrate of the display panel outside the display area, a bezel area may increase to cover these structures. 
       SUMMARY OF THE INVENTION 
       [0011]    Accordingly, the present invention is directed to a display device and a method of driving the same that substantially obviate one or more problems due to limitations and disadvantages of the related art. 
         [0012]    An advantage of the present invention is to provide a display device and a method of driving the same such that an auto-probe test pad and gate drivers are in a non-display area of a display panel in a configuration to minimize the non-display area. Thereby saving space and minimizing the bezel area of the display device. 
         [0013]    Additional advantages and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objectives and other advantages of the invention may be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings. 
         [0014]    One exemplary embodiment of the invention includes a display device, including a display panel including a first non-display area, a second non-display area, a main active area, and a sub active area, wherein the main active area and the sub active area each includes a matrix of sub-pixels; a data driver in the first non-display area to provide image data to the matrices of sub-pixels; a main gate driver in the second non-display area to provide a corresponding gate signal to each sub-pixel in the main active area; a sub gate driver in the second non-display area to provide a corresponding gate signal to each sub-pixel in the sub active area; an auto-probe test pad in the non-display area for transmitting a first start signal received from an auto-probe signal generating device to one of the main gate driver and the sub gate driver while testing the display panel; and a signal transmission circuit to transmit signals between the main gate driver and the sub gate driver. 
         [0015]    A second exemplary embodiment of the invention includes a display device, including a lower substrate, a display area, a data driver, a gate driver, and a signal transmission circuit. The display area includes a main display area and a sub display area, each of which consists of sub-pixels disposed on the lower substrate. A data driver transmits a data signal to the main display area and the sub display area. The gate driver includes a main gate driver transmitting a gate signal to the main display area, and a sub gate driver transmitting a gate signal to the sub display area. The signal transmission circuit transmits signals, which are output from input and output terminals of the main gate driver and the sub gate driver, in a first direction or in a second direction. 
         [0016]    It is to be understood that both the foregoing general description and the following detailed description of the present invention are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    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: 
           [0018]      FIG. 1  is a block diagram illustrating a display device; 
           [0019]      FIG. 2  is a diagram illustrating a sub-pixel shown in  FIG. 1 ; 
           [0020]      FIG. 3  is a diagram illustrating a display panel according to an experimental example of the related art; 
           [0021]      FIG. 4  is a diagram illustrating part of a display panel according to an experimental example of the related art; 
           [0022]      FIGS. 5A and 5B  are waveform diagrams illustrating an auto-probe start signal of a display panel according to an experimental example of the related art; 
           [0023]      FIG. 6  is a schematic view illustrating a display panel according to the embodiments of the present disclosure; 
           [0024]      FIGS. 7A, 7B, 8A, and 8B  are diagrams illustrating a waveform of an auto-probe start signal on a display panel according to the embodiments of the present disclosure; 
           [0025]      FIG. 9  is a diagram illustrating part of a display panel according to the first embodiment of the present disclosure; 
           [0026]      FIG. 10  is a diagram illustrating part of a display panel according to an modified example of the first embodiment of the present disclosure; 
           [0027]      FIG. 11  is a waveform diagram illustrating a signal applied to a test transistor according to driving conditions; 
           [0028]      FIGS. 12 and 13  are diagrams illustrating a flow of a start signal applied to a display panel according to the first embodiment of the present disclosure or a modified example thereof; 
           [0029]      FIG. 14  is a diagram illustrating a part of a display panel according to a second embodiment of the present disclosure; 
           [0030]      FIG. 15  is a diagram illustrating part of a display panel according to a modified example of the second embodiment of the present disclosure; 
           [0031]      FIG. 16  is a waveform diagram illustrating a signal which is applied to a test transistor according to driving conditions; 
           [0032]      FIGS. 17 and 18  are diagrams illustrating a flow of a start signal which is applied to a display panel according to the second embodiment of the present disclosure or a modified example thereof; 
           [0033]      FIG. 19  is a diagram illustrating part of a display panel according to a third embodiment of the present disclosure; 
           [0034]      FIGS. 20 and 21  are waveform diagrams illustrating a signal applied to a test transistor according to driving conditions; and 
           [0035]      FIG. 22  is a diagram illustrating the flow of a start signal applied to a display panel according to the third embodiment of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0036]    Reference will now be made in detail embodiments of the invention by examples of which are illustrated in the accompanying drawings. Hereinafter, detailed embodiments of the present disclosure are described in conjunction with the accompanying drawings. 
         [0037]    A display device according to the present disclosure can be included in a TV, a set-top box, a navigation system, an image player, a Blu-ray player, a personal computer (PC), a home theater, a mobile phone, or the like. A display panel of the display device may be selected from technologies including an Organic Light Emitting Display (OLED), a Quantum Dot Display (QDD), a Liquid Crystal Display (LCD), or a Plasma Display Panel (PDP), but aspects of the present disclosure are not limited thereto. 
         [0038]    For the LCD or the OLED, a display panel is manufactured and a test process is conducted to test the display panel. In the test process, an auto-probe test is used to test electrical features of the display panel (e.g., a line shortage test and a lighting test). 
         [0039]    The auto-probe test is conducted in a manner that a probe needle is put in contact with an auto-probe test pad (hereinafter, referred to as an “AP pad”) formed on a lower substrate of the display panel and then an electrical signal is applied. 
         [0040]      FIG. 1  is a block diagram illustrating a display device, and  FIG. 2  is a diagram schematically illustrating a sub-pixel shown in  FIG. 1 . 
         [0041]    As shown in  FIG. 1 , a display device includes an image supplier  110 , a timing controller  120 , a gate driver  130 , a data driver  140 , a display panel  150 , and a power supply  180 . 
         [0042]    The image supplier  110  performs image processing on a data signal, and outputs the data signal together with a vertical sync signal, a horizontal sync signal, a data enable signal, and a clock signal. Through a low voltage differential signaling (LVDS) interface or a transition minimized differential signaling (TMDS) interface, the image supplier  110  supplies the vertical sync signal, the horizontal signal, the data enable signal, the clock signal, and the data signal to the timing controller  120 . 
         [0043]    The timing controller  120  receives a data signal DATA from the image supplier  110 , and outputs a gate timing control signal GDC for controlling an operation timing of the gate driver  130 , and a data timing control signal DDC for controlling an operation timing of the data driver  140 . 
         [0044]    Through a communication interface, the timing controller  120  also outputs the data signal DATA together with the gate timing control signal GDC and the data timing control signal DDC. 
         [0045]    In response to the gate timing control signal GDC received from the timing controller  120 , the gate driver  130  outputs a gate signal (or a scan signal) while shifting a level of a gate voltage. The gate driver  130  includes a level shifter and a shift register. 
         [0046]    The gate driver  130  supplies the gate signal to a matrix of sub-pixels SP included in the display panel  150  through gate lines GL 1  to GLm. The gate driver  130  may be formed separately as an integrated circuit (IC), or may be integrally formed on the display panel  150  in a Gate In Panel (GIP) method. 
         [0047]    In response to the data timing control signal DDC received from the timing controller  120 , the data driver  140  samples and latches the data signal DATA, converts the data signal DATA into an analog signal in response to a gamma reference voltage, and outputs the analog signal. Through data lines DL 1  to DLn, the data driver  140  supplies the data signal DATA to the matrix of sub-pixels SP included in the display panel  150 . As mentioned, the data driver  140  may be formed as an integrated circuit (IC). 
         [0048]    The power supply  180  generates and outputs voltages Vout, Vgh, Vgl and GND based on an externally supplied input voltage. A high potential voltage Vout, a gate high voltage Vgh, a gate low voltage Vgl and a low potential voltage GND, which are output from the power supply  180 , are used in various components included in the display device. For example, the high potential voltage Vout and the low potential voltage GND may be supplied to the display panel  150 , and the gate high voltage Vgh and the gate low voltage Vgl may be supplied to the gate driver  130 . 
         [0049]    In response to the gate signal received from the gate driver  130  and the data signal received from the data driver  140 , the display panel  150  displays an image. The display panel  150  includes a lower substrate and an upper substrate. Sub-pixels SP are formed between the lower substrate and the upper substrate. 
         [0050]    As shown in  FIG. 2 , one sub-pixel includes a switching thin film transistor (TFT) SW connected between a gate line GL 1  and a data line DL 1  (or formed at a crossing of a gate line GL 1  and a data line DL 1 ), and a pixel circuit PC which operates in response to a data signal DATA transmitted through the switching TFT SW. Sub-pixels may be configured as liquid-crystal cells of a Liquid Crystal Display (LCD) panel, or may be configured as organic light emitting devices of an organic light emitting display panel. 
         [0051]    In a case where the display panel  150  is an LCD panel, the display panel  150  may operate in a Twisted Nematic (TN) mode, a Vertical Alignment (VA) mode, an In Plane Switching (IPS) mode, a Fringe Field Switching (FFS) mode, or an Electrically Controlled Birefringence (ECB) mode. In a case where the display panel is an OLED panel, the display panel  150  may be a top-emission type, a bottom-emission type, or a dual-emission type. 
         [0052]    The above-described display device may display an image as the sub-pixels of the display panel  150  emits or transmits light based on voltages Vout and GND output from the power supply  180 , a gate signal output from the gate driver  130 , and a data signal DATA output from the data driver  140 . 
         [0053]    [Experimental Example of the Related Art] 
         [0054]      FIG. 3  is a diagram schematically illustrating a display panel according to an experimental example of the related art;  FIG. 4  is a block diagram illustrating part of a display panel according to an experimental example of the related art; and  FIGS. 5A and 5B  are waveform diagrams illustrating auto-probe start signals of a display panel according to an experimental example of the related art. 
         [0055]    As shown in  FIGS. 3 to 5B , the data driver  140  is formed in a first non-display area NA 1  of the display panel  150 , which is located on an upper portion of the display panel  150 . Gate drivers  130 M and  130 S are formed in a second non-display area NA 2  of the display panel  150 , which are located on a side portion of the display panel  150 . The matrix of sub-pixels are formed in an active area AA. 
         [0056]    In the gate drivers  130 M and  130 S, a main gate driver  130 M and a sub gate driver  130 S may be formed on the lower substrate of the display panel  150  in a GIP method such that the main gate driver  130 M and the sub gate driver  130 S are able to operate separately. 
         [0057]    The main gate driver  130 M provides a gate signal to a main display active area Main AA of the display panel  150 , and the sub gate driver  130 S provides a gate signal to a sub-display active area Sub AA of the display panel  150 . 
         [0058]    The gate drivers  130 M and  130 S have a structure as described above. Each active area of the display panel  150  is able to be driven individually as a gate signal is supplied in a forward direction FWD or in a reverse direction REV. In the drawings, for convenience of explanation, a direction from bottom to top on the display panel  150  is defined as a forward direction FWD, and a direction from top to bottom on the display panel  150  is defined as a reverse direction REV. However, aspects of the present disclosure are not limited thereto. 
         [0059]    Meanwhile, in a case where the gate drivers  130 M and  130 S have a structure as described above, an auto-probe test may be conducted only when AP pads AP 1  and AP 2  supplying electrical signals are formed in the main gate driver  130 M and the sub gate driver  130 S, respectively. In the experimental example, first and second AP pads AP 1  and AP 2  are formed in a pad area in a non-display area for use while performing the auto-probe test. As illustrated in  FIG. 4 , the first AP pad AP 1  is a pad which transmits, through a first start signal line, a first start signal VST 1  for driving the sub gate driver  130   s.  The second AP pad AP 2  is a pad which transmits, through a second start signal line, a second start signal VST 2  for driving the main gate driver  130 M. Start signals are used to drive the main gate driver  130 M and the sub gate driver  130 S. 
         [0060]    As illustrated in  FIGS. 5A and 5B , the first and second start signals VST 1  and VST 2  transmitted through the first and second AP pads AP 1  and AP 2  are transmitted to the gate drivers  130 M and  130 S. The first and second start signals VST 1  and VST 2  may be transmitted through the first and second AP pads AP 1  and AP 2  only when the auto-probe test is in process, and may be transmitted through the data driver  140  after the auto-probe test is done. 
         [0061]    The above experimental example is a case where two AP pads AP 1  and AP 2  are used. Accordingly, as shown in  FIG. 5A , if only the first start signal VST 1  is transmitted from an AP signal generating device (not shown), the sub gate driver  130 S alone may operate. Alternatively, as shown in  FIG. 5B , if only the second start signal VST 2  is transmitted from the AP signal generating device, the gate driver  130 M alone may operate. 
         [0062]      FIG. 4  is an example in which a start signal is configured to separately drive the main gate driver  130 M and the sub gate driver  130 S. Thus, it is possible to change a driving method of the gate drivers  130 M and  130 S to a separate driving method, an individual driving method, a combined driving method depending on a changed order of the start signals VST 1  and VST 2 , or characteristics thereof. 
         [0063]    However, the main gate driver  130 M and the sub gate driver  130 S are separate from each other, so both of the two start signals need to be applied in order to drive both of the main gate driver  130 M and the sub gate driver  130 S and perform the auto-probe test. 
         [0064]    Under this circumstance, to perform the auto-probe test described above, the two AP pads AP 1  and AP 2  have to be formed in the first non-display area NA 1  on the display panel  150 . In this case, one more pad has to be formed in the bezel area of the display panel, so that it may add a limitation to design of the display panel and the bezel area may increase in size. 
         [0065]    In addition, AP pads and an output from the AP signal generating device are added in the experiment example, so it is difficult to use (or utilize) an existing test device because it cannot solve the problems regarding generation of a start signal and timing control. Hereinafter, drawbacks of the experimental example will be explained, and another experimental example will be described as a way of solving the drawbacks. 
       Embodiment 1 
       [0066]      FIG. 6  is a schematic view illustrating a display panel according to the present disclosure;  FIGS. 7A, 7B, 8A, and 8B  are diagrams illustrating a waveform of an auto-probe start signal on a display panel according to the the present disclosure;  FIG. 9  is a block diagram illustrating part of a display panel according to the first embodiment of the present disclosure;  FIG. 10  is a block diagram illustrating another part of a display panel according to another aspect of the first embodiment of the present disclosure;  FIG. 11  is a waveform diagram illustrating a signal applied to a signal transmission circuit ST according to driving conditions; and  FIGS. 12 and 13  are block diagrams illustrating a flow of a start signal applied to a display panel according to the first embodiment of the present disclosure. 
         [0067]    As illustrated in  FIG. 6  , a data driver  140  is formed in a first non-display area NA 1  which is in an upper portion of a display panel  150 . Gate drivers  130 M and  130 S are formed in a second non-display area NA 2  which are on a side portion of the display panel. 
         [0068]    The gate drivers  130 M and  130 S are formed, in a Gate In Panel (GIP) method, on a lower substrate of the display panel  150  such that a main gate driver  130 M and a sub gate driver  130 S are able to be driven individually. 
         [0069]    The main gate driver  130 M provides a gate signal to a main active area Main AA of the display panel  150 , and the sub gate driver  130 S provides a gate signal to a sub display active area Sub AA of the display panel  150 . The sub gate driver  130 S provides a gate signal to each of a first gate line GL 1  to the N th  gate line GLn which are connected to the sub display active area Sub AA. The main gate driver  130 M provides a gate signal to each of the N+1 th  gate line GLN+1 to the M th  gate line GLm which are connected to the main display area Main AA. 
         [0070]    As the gate drivers  130 M and  130 S have the aforementioned structure, the display panel  150  is provided a gate signal in a forward direction FWD or in a reverse direction REV so that each active area may be driven individually (independently). In the drawings, for convenience of explanation, a direction from bottom to top on the display panel  150  is defined as a forward direction FWD, and a direction from top to bottom on the display panel  150  is defined as a reverse direction REV. However, aspects of the present disclosure are not limited thereto. 
         [0071]    In the second and third embodiments of the present disclosure, which are described in detail below, along with the first embodiment, a main gate driver  130 M and a sub gate driver  130 S have a signal transmission circuit connected therebetween to sequentially or simultaneously drive the main gate driver  130 M and the sub gate driver  130 S in the forward direction or may be driven sequentially or simultaneously in the reverse direction, with relative timing as shown in  FIGS. 7 and 8 . 
         [0072]    Because the signal transmission circuit ST is connected between the main gate driver  130 M and the sub gate driver  130 S, only a single AP pad is used. A start signal transmitted through the single AP pad is transferred to the gate drivers  130 M and  130 S. The start signal may be transmitted through the single AP pad during the auto-probe test, and may be transmitted through a data driver after the test. The start signal is used as a signal necessary to drive the main gate driver  130 M and the sub gate driver  130 S. Meanwhile,  FIGS. 7A, 7B, 8A, and 8B  illustrate an example in which only a first start signal VST 1  is transmitted because a single AP pad is used. However, a second start signal VST 2  may be used instead of the first start signal VST 1 . 
         [0073]    As shown in  FIG. 7A , in a case where the main gate driver  130 M and the sub gate driver  130 S are driven sequentially in the forward direction FWD, operations (the N+1 th  gate line n+1 to the M th  gate line m) of the main display active area Main AA are performed after operations (the first gate line  1  to the N th  gate line n) of the sub-display active area Sub AA of the display panel  150  are completed. As shown in  FIG. 7B , in a case where the main gate driver  130 M and the sub gate driver  130 S are driven sequentially in the reverse direction REV, operations (the first gate line  1  to the N th  gate line n) of the sub-display active area Sub AA of the display panel  150  are performed after operations (the N+1 th  gate line n+1 to the M th  gate line m) in the main display active area Main AA are completed. 
         [0074]    As shown in  FIG. 8A , in a case where the main gate driver  130 M and the sub gate driver  130 S are driven simultaneously in the forward direction FWD, operations (the first gate line  1  to the N+1 th  gate line n+1) of the main display active area Main AA and the sub-display active area Sub AA of the display panel  150  are performed simultaneously. As shown in  FIG. 8B , in a case where the main gate driver  130 M and the sub gate driver  130 S are driven simultaneously in the reverse direction REV, operations (the N th  gate line n to the M th  gate line m) of the main display active area Main AA and the sub-display active area Sub AA of the display panel  150  are performed simultaneously. 
         [0075]    Hereinafter, is an example in which a signal transmission circuit is connected between the main gate driver  130 M and the sub gate driver  130 S. The signal transmission circuit may be located between the AP pad and the main gate driver  130 M, between the main gate driver  130 M and the sub gate driver  130 S, on an outer side of the main gate driver  130 M, on an outer side of the sub gate driver  130 S, or any other suitable position. 
         [0076]    In the first embodiment shown in  FIGS. 9, 11, and 12 , the main gate driver  130 M and the sub gate driver  130 S operate based on a first start signal VST 1  which is transmitted along a first signal line through an AP pad AP. 
         [0077]    As illustrated in  FIG. 9 , a signal transmission circuit ST is connected between the main gate driver  130 M and the sub gate driver  130 S. The signal transmission circuit ST transfers a signal output from the N th  forward direction terminal FWDn of the sub gate driver  130 S to the N+1 th  forward direction terminal FWDn+1 of the main gate driver  130 M. 
         [0078]    The signal transmission circuit ST includes a first transistor Ta and a second transistor Tb. In this and the following examples, the first transistor Ta and the second transistor Tb, and all other signal transmission transistors, are N-type transistors. However, the signal transistors may be P-type transistors. The first transistor Ta includes a first electrode connected to the N th  forward direction terminal FWDn of the sub gate driver  130 S, and a second electrode connected to the N+1 th  forward direction terminal FWDn+1 of the main gate driver  130 M. The second transistor Tb includes a gate electrode connected to a first signal line VGH, a first electrode connected to a second signal line VEND, and a second electrode connected to a gate electrode of the first transistor Ta. A first signal transmitted along the first signal line VGH is generated and controlled by the power supply  180 , shown in  FIG. 1 . A second signal transmitted along the second signal line VEND may use the signal from the AP pad, but aspects of the present disclosure are not limited thereto. 
         [0079]    Once the first signal transmitted along the first signal line VGH is changed from logic low level L to logic high level H, the second transistor Tb is turned on. Once the second signal VEND transmitted along the second signal line VEND through the first electrode of the second transistor Tb is changed from logic low level L to logic H, the first transistor Ta is turned on. 
         [0080]    Once the first transistor Ta is turned on, the signal transmission circuit ST is activated. Once the signal transmission circuit ST is activated, a signal output from the Nth forward direction terminal FWDn of the sub gate driver  130 S is transferred to the N+1 th  forward direction terminal FWDn+1 of the main gate driver  130 M. 
         [0081]    The first signal transmitted along the first signal line VGH may use a gate high voltage supplied to the gate drivers  130 M and  130 S, but aspects of the present disclosure are not limited thereto. In addition, the second signal transmitted along the second signal line VEND may use a gate high voltage supplied to the gate driver  130 M and  130 S, but aspects of the present disclosure are not limited thereto. 
         [0082]    Further, as illustrated in  FIG. 11 , in a case when the data driver provides the first and/or second signals rather than the case when the auto probe AP generates these signals, the second signal is changed from logic high level H to logic low level L. In particular, the second signal transmitted along the second signal line VEND has to be changed from logic high level H to logic low level L, but the first signal transmitted along the first signal line VGH is able to remain at logic high level H. 
         [0083]    As shown in  FIG. 9 , the N th  reverse direction terminal REVn of the sub gate driver  130 S is connected to a third signal line VGL. The third signal line VGL supplies a gate-low voltage at logic low level L. The gate low voltage is output from a power supply or a level shifter (not shown). Once a gate low voltage at logic low level L is supplied, the sub gate driver  130 S stops being driven in the reverse direction REV based on the design as to which direction the data is driven. 
         [0084]    The N+1 th  forward direction terminal FWDn+1 and the M th  reverse direction terminal REVm (the first reverse direction terminal) of the main gate driver  130 M are connected to the second electrode of the first transistor Ta. Accordingly, a signal output from the Nth forward direction terminal FWDn of the sub gate driver  130 S may be transferred to the N+1 th  forward direction terminal FWDn+1 and the M th  reverse direction terminal REVm of the main gate driver  130 M. The signal output from one of the sub gate driver  130 S or the main gate driver  130 M devices is a trigger for controlling the other gate driver device. 
         [0085]    Referring to  FIG. 12 , the main gate driver  130 M performs a driving operation of the forward direction FWD based on a signal (FGOUTn) output from the N th  forward direction terminal FWDn of the sub gate driver  1305 . The M th  reverse direction terminal REVm of the main gate driver  130 M may receive a signal (FGOUTn in  FIG. 12 ) which is output from the N th  forward direction terminal FWDn of the sub gate driver  130 S. 
         [0086]    In the above-described first embodiment of the present disclosure, a start signal VST 1  is transferred from an AP pad AP, and, once the signal transmission circuit ST is activated, the sub gate driver  130 S and the main gate driver  130 M may be driven sequentially in the forward direction FWD. 
         [0087]    In another aspect of the first embodiment shown in  FIGS. 10, 11, and 13 , the main gate driver  130 M and the sub gate driver  130 S operate based on a second start signal VST 2  received through the second start signal line from an AP pad AP. 
         [0088]    In this aspect, the signal transmission circuit ST transmits a signal, which is output from the N+1 th  reverse direction terminal REVn+1 of the main gate driver  130 M, to the N th  reverse direction terminal REVn of the sub gate driver  130 S. 
         [0089]    The first transistor Ta includes a first electrode connected to the N th  reverse direction terminal REVn of the sub gate driver  130 S, and a second electrode connected to the N+1 th  reverse direction terminal REVn+1 of the main gate driver  130 M. The second transistor Tb includes a gate electrode connected to a first signal line VGH, a first electrode connected to a second electrode, and a second electrode connected to a gate electrode of the first transistor Ta. 
         [0090]    Once the first signal transmitted along the first signal line VGH is changed from logic low level L to logic high level H, the second transistor Tb is turned on. Once the second signal is transmitted through the first electrode of the second transistor Tb is changed from logic low level L to logic high level H, the first transistor Ta is turned on. 
         [0091]    Once the first transistor Ta is turned on, the signal transmission circuit ST is activated. Once the signal transmission circuit ST is activated, the signal output from the N+1 th  reverse direction terminal REVn+1 of the main gate drier  130 M is transferred to the N th  reverse direction terminal REVn of the sub gate driver  130 S. 
         [0092]    The first signal transmitted along the first signal line VGH may use a gate high voltage supplied to the gate driver  130 M and  130 S, but aspects of the present disclosure are not limited thereto. In addition, the second signal transmitted along the second signal line VEND may use a gate high voltage supplied to the gate driver  130 M and  130 S, but aspects of the present disclosure are not limited thereto. 
         [0093]    In the data driver driving case rather than an auto-probe AP driving case, the first and second signals are changed from logic high level H to logic low level L, as illustrated in  FIG. 11 . In particular, the second signal transmitted along the second signal line VEND has to be changed from logic high level H to logic low level L, but the first signal transmitted along the first signal line VGH is able to remain at logic high level H. 
         [0094]    The N+1 th  forward direction terminal FWDn+1 of the M th  reverse direction terminal REVm of the main gate driver  130 M are connected to the second start signal line, and the N+1 th  reverse direction terminal REVn+1 of the main gate driver  130 M is connected to the second electrode of the first transistor Ta. Accordingly, once the first transistor Ta is turned on, the N+1 th  reverse direction terminal REVn+1 of the main gate driver  130 M may be transferred to the N th  reverse direction terminal REVn of the sub gate driver  130 S. 
         [0095]    In the above-described aspect of the first embodiment of the present disclosure, a start signal VST 2  is transmitted from an AP pad AP, and, once the signal transmission circuit ST is activated, the main gate driver  130 M and the sub gate driver  130 S are driven sequentially in the reverse direction REV. 
       Embodiment 2 
       [0096]      FIG. 14  is a block diagram illustrating a part of a display panel according to a second embodiment of the present disclosure;  FIG. 15  is a block diagram illustrating part of a display panel according to another aspect of the second embodiment of the present disclosure;  FIG. 16  is a waveform diagram illustrating a signal which is applied to the signal transmission circuit ST according to driving conditions; and  FIGS. 17 and 18  are block diagrams illustrating a flow of a start signal which is applied to a display panel according to the second embodiment of the present disclosure or the other aspect thereof. 
         [0097]    In the second embodiment of the present disclosure, a main gate driver and a sub gate driver have a signal transmission circuit connected therebetween, and may be driven simultaneously in the forward direction or may be driven simultaneously in the reverse direction. 
         [0098]    As the signal transmission circuit is connected between the main gate driver and the sub gate driver, only a single AP pad is used. The AP pad may transfer a first start signal or a second start signal along a start signal line. 
         [0099]    In the second embodiment shown in  FIGS. 14, 16, and 17 , a main gate driver  130 M and a sub gate driver  130 S operate based on a first start signal VST 1  received through a first start signal line from an AP pad AP. 
         [0100]    A signal transmission circuit ST is between the main gate driver  130 M and the sub gate driver  130 S. The signal transmission circuit ST transmits the first start signal VST 1  to the N+1 th  forward direction terminal FWDn+1 of the main gate driver  130 M. 
         [0101]    The first transistor Ta includes a first electrode connected to the N th  reverse direction terminal REVn of the sub gate driver  130 S, and a second electrode connected to the N+1 th  forward direction terminal FWDn+1 of the main gate driver  130 . The second transistor Tb includes a gate electrode connected to a first signal line VGH, a first electrode connected to a second signal line VEND, and a second electrode connected to a gate electrode of the first transistor Ta. 
         [0102]    Once a first signal transmitted along the first signal line VGH is changed from logic low level L to logic high level H, the second transistor Tb is turned on. Once a second signal transmitted through the first electrode of the second transistor Tb is changed from logic low level L to logic high level H, the first transistor Ta is turned on. 
         [0103]    Once the first transistor Ta is turned on, the signal transmission circuit ST is activated. Once the signal transmission circuit ST is activated, the first start signal VST 1  is transferred to the N+1 th  forward direction terminal FWDn+1 of the main gate driver  130 M. 
         [0104]    The first signal transmitted along the first signal line VGH may use a gate high voltage supplied to a gate driver  130 M and  130 S, but aspects of the present disclosure are not limited thereto. The second signal transmitted along the second signal line VEND may use the gate high voltage supplied to the gate driver  130 M and  130 S, but aspects of the present disclosure are not limited. The gate high voltage is output from a power supply or a level shifter (not shown). 
         [0105]    In data driver driving case rather than an auto-probe AP driving case, the first and second signals are changed from logic high level H to logic low level L. The second signal transmitted along the second signal line VEND has to be changed from logic high level H to logic low level L, but the first signal transmitted along the first signal line VGH is able to remain at logic high level H. 
         [0106]    Referring to  FIG. 14 , the first forward direction terminal FWD 1  and the N th  reverse direction terminal REVn of the sub gate driver  130 S are connected to the first start signal line from VST 1 . The first start signal line is connected to the first electrode of the first transistor Ta. The second electrode of the first transistor Ta is connected to the N+1 th  forward direction terminal FWDn+1 and the M th  reverse direction terminal REVm of the main gate driver  130 M. 
         [0107]    The N+1 th  forward direction terminal FWDn+1 and the M th  reverse direction terminal REVm of the main gate driver  130 M are connected to the second start signal line. The second start signal line is also connected to the second electrode of the first transistor Ta. Accordingly, once the first transistor Ta is turned on, the main gate driver  130 M may receive the first start signal VST 1  along the first start signal line. 
         [0108]    Referring to  FIG. 17 , when the signal transmission circuit ST is activated, the main gate driver  130 M and the sub gate driver  130 S are able to simultaneously receive the first start signal VST 1  from the N+1 th  forward direction terminal FWDn+1 and the first forward direction terminal FWD 1 , respectively, so that the main gate driver  130 M and the sub gate driver  130 S are driven simultaneously in the forward direction FWD (see the dotted line indicating the flow of {circle around (1)}VST 1 ). In addition, the main gate driver  130 M and the sub gate driver  130 S are able to receive the first start signal VST 1  from the M th  reverse direction terminal REVm and the N th  reverse direction terminal REVn, so that the main gate driver  130 M and the sub gate driver  130 S are driven simultaneously in the reverse direction REV (see the dotted line indicating the flow of {circle around (2)}VST 1 ). Therefore, the main gate driver  130 M and the sub gate driver  130 S may be driven simultaneously in two directions. 
         [0109]    Thus, in a first aspect of the second embodiment of the present disclosure, a start signal VST 1  is transferred from an AP pad AP, and, once the signal transmission circuit ST is activated, the sub gate driver  130 S and the main gate driver  130 M are driven simultaneously in the forward direction FWD and in the reverse direction REV. 
         [0110]    In another aspect of the second embodiment, as shown in  FIGS. 15, 16 , and  18 , a main gate driver  130 M and a sub gate driver  130 S operate based on a second start signal VST 2  received through a second start signal line from an AP pad AP. 
         [0111]    A signal transmission circuit ST is connected between the main gate driver  130 M and the sub gate driver  130 S. The signal transmission circuit ST transmits the second start signal VST 2  to the N th  reverse direction terminal REVn of the sub gate driver  130 S. 
         [0112]    The first transistor Ta includes a first electrode connected to the N th  reverse direction terminal REVn of the sub gate driver  130 S, and a second electrode connected to the N+1 th  reverse direction terminal REVn+1 of the main gate driver  130 M. The second transistor Tb includes a gate electrode connected to a first signal line VGH, a first electrode connected to a second signal line VEND, and a second electrode connected to a gate electrode of the first transistor Ta. 
         [0113]    Once a first signal transmitted along the first signal line VGH is changed from logic low level L to logic high level H, the second transistor Tb is turned on. Once a second signal transmitted through the first electrode of the second transistor Tb is changed from logic low level L to logic high level H, the first transistor Ta is turned on. 
         [0114]    Once the first transistor is turned on, the signal transmission circuit ST is activated. Once the signal transmission signal ST is activated, the second start signal VST 2  is transferred to the N th  reverse direction terminal REVn of the sub gate driver  130 S. 
         [0115]    The first signal transmitted along the first signal line VGH may use a gate high voltage supplied to a gate driver  130 M and  130 S, but aspects of the present disclosure are not limited thereto. The second signal transmitted along the second signal line VEND may use the gate high voltage supplied to the gate driver  130 M and  130 S, but aspects of the present disclosure are not limited thereto. The gate high voltage is output from a power supply  180  or a level shifter (not shown). 
         [0116]    In a data driver driving case rather than an auto-probe driving case, as shown in  FIG. 16 , the second signal is changed from logic high level H to logic low level L. In particular, the second signal transmitted along the second signal line VEND has to be changed from logic high level H to logic low level L, but the first signal transmitted along the first signal line VGH is able to remain at logic high level H. 
         [0117]    Referring to  FIG. 15 , the first forward direction terminal FWD 1  and the N th  reverse direction terminal REVn of the sub gate driver  1305  are connected to the first electrode of the first transistor Ta. The second electrode of the first transistor Ta is connected to the first start signal line from VST 1 . 
         [0118]    The N+1 th  forward direction terminal FWDn+1 and the M th  reverse direction terminal REVm of the main gate driver  130 M are connected to the second start signal line from VST 2 . The second start signal line is connected to the second electrode of the first transistor. Accordingly, once the first transistor Ta is turned on, the sub gate driver  130 S is able to receive the second start signal transmitted along the second start signal line. 
         [0119]    Referring to  FIG. 18 , the main gate driver  130 M and the sub gate driver  130 S are able to simultaneously receive the second start signal VST 2  from the N+1 th  forward direction terminal FWDn+1 and the first forward direction terminal FWD 1 , respectively, so that the main gate driver  130 M and the sub gate driver  130 S are driven simultaneously in the forward direction FWD (see the dotted line indicating the flow of {circle around (1)}VST 2 ). In addition, the main gate driver  130 M and the sub gate driver  130 S are able to simultaneously receive the second start signal VST 2  from the M th  reverse direction terminal REVm and the N th  reverse direction terminal REVn, respectively, so that the main gate driver  130 M and the sub gate driver  1305  are driven in the reverse direction REV (see the dotted line indicating the flow of {circle around (2)}VST 2 ). Therefore, the main gate driver  130 M and the sub gate driver  130 S may be driven simultaneously in two directions. 
         [0120]    Considering the second embodiment and the modified example thereof, the main gate driver  130 M and the sub gate driver  130 S use the first and second start signals VST 1  and VST 2  having the same waveform in an auto-probe AP driving case. However, in a data driver driving case, the first start signal VST 1  and the second start signal VST 2  have to be separate temporally, using the signal transmission circuit ST. 
         [0121]    In the above-described modified example of the second embodiment, a start signal VST 2  is transferred from the AP pad AP, and, once the signal transmission circuit ST is activated, the main gate driver  130 M and the sub gate driver  130 S are driven simultaneously in the forward direction FWD and in the reverse direction REV. 
       Embodiment 3 
       [0122]      FIG. 19  is a block diagram illustrating part of a display panel according to a third embodiment of the present disclosure;  FIGS. 20 and 21  are waveform diagrams illustrating a signal applied to a signal transmission circuit ST 2  according to driving conditions; and  FIG. 22  is a block diagram illustrating the flow of a start signal applied to a display panel according to the third embodiment of the present disclosure. 
         [0123]    In the third embodiment of the present disclosure, a main gate driver and a sub gate driver have a signal transmission circuit connected therebetween and may be able to be driven sequentially in a forward direction or in a reverse direction. 
         [0124]    As the signal transmission circuit is between the main gate driver and the sub gate driver, only a single AP pad is used. The AP pad is able to transmit either a first start signal or a second start signal through a start signal line. In this example, the AP pad transmits the first start signal. 
         [0125]    In the third embodiment as shown in  FIGS. 19 to 22 , a main gate driver  130 M and a sub gate driver  130 S operate based on a first start signal VST 1  received through the first start signal line from the AP pad. 
         [0126]    A signal transmission circuit ST 2  is connected between a main gate driver  130 M and a sub gate driver  130 S. The signal transmission circuit ST 2  transmits a signal output from the N th  forward direction terminal FWDn of the sub gate driver  130 S to the N+1 th  forward direction terminal FWDn+1 of the main gate driver  130 M. In addition, the signal transmission circuit ST 2  transmits a signal output from the N+1 th  forward direction terminal FWDn+1 of the main gate driver  130 M to the N th  forward direction terminal FWDn of the sub gate driver  130 S. 
         [0127]    The signal transmission circuit ST 2  transmits a signal output from the N th  reverse direction terminal REVn of the sub gate driver  1305  to the N+1 th  reverse direction terminal REVn+1 of the main gate driver  130 M. In addition, the signal transmission circuit ST 2  transmits a signal output from the N+1 th  reverse direction terminal REVn+1 of the main gate driver  130 M to the N th  reverse direction terminal REVn of the sub gate driver  1305 . 
         [0128]    The signal transmission circuit ST 2  includes a first transistor Ta to a sixth transistor Tf. 
         [0129]    The first transistor Ta includes a first electrode connected to the N th  forward direction terminal FWDn of the sub gate driver  130 S, and a second electrode connected to the N+1 th  forward direction terminal FWDn+1 of the main gate driver  130 M. The second transistor Tb includes a gate electrode connected to a first signal line VGH, a first electrode connected to the second signal line VEND, and a second electrode connected to a gate electrode of the first transistor Ta. The third transistor Tc includes a gate electrode connected to a fourth signal line REVL, a first electrode connected to a third signal line VGL, and a second electrode connected to the gate electrode of the first transistor Ta. The first transistor Ta to the third transistor Tc constitute a first signal transmission circuit which controls a sequential driving operation of the forward direction FWD. 
         [0130]    Referring to  FIG. 20 , once a first signal transmitted along the first signal line VGH is supplied, the second transistor Tb is turned on. Once a second signal VEND transmitted through the first electrode of the second transistor Tb is changed from logic low level L to logic high level H, the first transistor Ta is turned on. At this point, a fourth signal transmitted along the fourth signal line REVL remains at logic low level L, and a fifth signal transmitted along the fifth signal line FWDL remains at logic high level H. 
         [0131]    Once the first portion of the signal transmission circuit ST 2  (Ta to Tc) is activated, a signal output from the N th  forward direction terminal FWDn of the sub gate driver  1305  is transmitted to the N+1 th  forward direction terminal FWDn+1 of the main gate driver  130 M. In such an auto-probe AP driving condition, the sub gate driver  1305  and the main gate driver  130 M are driven sequentially in the forward directions FWD. 
         [0132]    The fourth transistor Td includes a first electrode connected to the N th  reverse direction terminal REVn of the sub gate driver  130 S, and a second electrode connected to the N+1 th  reverse direction terminal REVn+1 of the main gate driver  130 M. The fifth transistor Te includes a gate electrode connected to the first signal line VGH, a first electrode connected to the second signal line VEND, and a second electrode connected to a gate electrode of the fourth transistor Td. The sixth transistor Tf includes a gate electrode connected to a fifth signal line FWDL, a first electrode connected to the third signal line VGL, and a second electrode connected to the gate electrode of the fourth transistor Td. The fourth transistor Td to the sixth transistor Tf constitute a second portion of the signal transmission circuit ST 2  which controls a sequential driving operation of the reverse direction REV. 
         [0133]    Referring to  FIG. 21 , once a first signal transmitted along the first signal line VGH is changed from logic low level L to logic high level H, the fifth transistor Te is turned on. Once a second signal VEND transmitted through the first electrode of the fifth transistor Te is changed from logic low level L to logic high level H, the fourth transistor Td is turned on. At this point, the fourth signal transmitted along the fourth signal line REVL remains at logic high level H, and the fifth signal transmitted along the fifth signal line FWDL remains at logic low level L. 
         [0134]    Once the second portion of the signal transmission circuit STS 2  (Td to Tf) is activated, a signal output from the N+1 th  reverse direction terminal REVn+1 of the main gate driver  130 M is transmitted to the N th  reverse direction terminal REVn of the sub gate driver  1305 . In such an auto-probe AP driving condition, the main gate driver  130 M and the sub gate driver  130 S are driven sequentially in the reverse direction REV. 
         [0135]    The first signal transmitted along the first signal line VGH may use a gate high voltage supplied to a gate driver  130 M and  130 S, but aspects of the present disclosure are not limited thereto. The second signal transmitted along the second signal line VEND may use the gate high voltage supplied to the gate driver  130 M and  130 S, but aspects of the present disclosure are not limited thereto. The gate high voltage is output from a power supplier and a level shifter. 
         [0136]    In data driver driving mode rather than an auto-probe AP driving mode, the second signal is changed from logic high level H to logic low level L. In particular, the second signal transmitted along the second signal line VEND has to be changed from logic high level H to logic low level L, but the first signal transmitted along the first signal line VGH is able to remain at logic high level H. 
         [0137]    The fourth signal transmitted along the fourth signal line REVL and the fifth signal transmitted along the fifth signal line FWDL are maintained at respective levels reversed to each other. The fourth and fifth signal may be output from the power supply or the level shifter (not shown), but aspects of the present disclosure are not limited thereto. 
         [0138]    Referring to  FIG. 19 , the first forward direction terminal FWD 1  of the sub gate driver  130 S and the M th  reverse direction terminal REVm of the main gate driver  130 M are connected to the first start signal line. The second start signal line is connected to the N+1 th  forward direction terminal FWDn+1 of the main gate driver  130 M. 
         [0139]    Referring to  FIG. 22 , once the first portion of the signal transmission circuit ST 2  (Ta to Tc) is activated, the sub gate driver  130 S performs a sequential driving operation based on the first start signal VST 1  transmitted from the first forward direction terminal FWD 1 , and then outputs the N th  forward direction signal FGOUTn. The main gate driver  130 M performs a sequential driving operations based on the N th  forward direction signal FGOUTn transmitted to the N+1 th  forward direction terminal FWDn+1. That is, the sub gate driver  130 S and the main gate driver  130 M are driven sequentially in the forward direction FWD (see the dotted line indicating the flow of {circle around (1)}VST 1 ). 
         [0140]    Once the second signal portion of the transmission circuit ST 2  (Td to Tf) is activated, the main gate driver  130 M performs a sequential driving operation based on the first start signal VST 1  transmitted to the M th  reverse direction terminal REFVm, and then outputs the N+1 th  reverse direction signal RGOUTn+1. The sub gate driver  1305  performs a sequential driving operation based on the N+1 th  reverse direction signal RGOUTn+1 transmitted to the N th  reverse direction terminal REVn. That is, the main gate driver  130 M and the sub gate driver  130 S are driven sequentially in the reverse direction REV (see the dotted line indicating the flow of {circle around (2)}VST 1 ). Therefore, the main gate driver  130 M and the sub gate driver  130 S may be driven sequentially in two directions. 
         [0141]    In the third embodiment of the present disclosure, a start signal VST 1  is transmitted from the AP pad AP, and, once any one of the first portion of the signal transmission circuit ST 2  (Ta to Tc) and the second portion of the signal transmission circuit ST 2  (Td to Tf) is activated, the sub gate driver  130 S and the main gate driver  130 M perform a sequential driving operation of the forward direction FWD or the reverse direction REV. 
         [0142]    According to the above embodiments of the present disclosure, input and output terminals of the main gate driver  130 M and the sub gate driver  130 S are connected (to transmit a signal in the first direction (forward) or in the second direction (reverse)), or a signal transmission circuit is connected between the input and output terminals to transmit a start signal, so that auto-probe test may be conducted with only a single AP pad. 
         [0143]    As such, the present disclosure is able to embody a display panel for which an auto-probe test can be conducted with a single AP pad and a signal transmission circuit that is connected between two electrically separate gate drivers to transmit a signal, so that it may solve a problem led by the limitation to a non-active display or bezel region or an increase in size of the bezel area. In addition, the present disclosure is able to operate two electrically separate gate drivers in various ways according to a configuration of the signal transmission circuit, and it may be used in various fields and use (utilize) an existing inspecting device.