Abstract:
A liquid crystal display includes a first substrate having a plurality of pixel electrodes arranged in a matrix, a plurality of row terminals and common electrode terminals arranged on one side of two adjacent sides of the first substrate, a plurality of column terminals and common electrode terminals arranged on the other side of the two adjacent sides of the first substrate; a second substrate arranged to be opposite to the first substrate and to interpose a liquid crystal display with the first substrate and having a counter electrode for performing liquid crystal display by applying a voltage across the pixel electrodes and the counter electrode. The conductive region being connected to at least one of the common electrode terminals to apply a common potential to the counter electrode. Instead of using a common drive circuit, a single conductive region is formed along only a single one of the two remaining sides of the first substrate so as to allow for measuring of at least one of a voltage drop and a voltage signal delay occurring at a substantially central portion of the matrix.

Description:
This is a Continuation of U.S. patent application Ser. No. 09/158,466 filed on Sep. 22, 1998, which is a Continuation of U.S. patent application Ser. No. 09/009,671 filed on Jan. 20, 1998, now U.S. Pat. No. 5,831,709. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a liquid crystal display (or “LCD”) device which provides a structure that allows for detection of the distortion of the common voltage resulting from a delay time in application of the common voltage. More specifically, the present invention relates to a liquid crystal display device including a common line which eliminates the need for a common drive circuit and which is arranged to allow for detection of an amount of distortion of the common voltage so that such distortion can be corrected. 
     2. Description of the Related Art 
     As seen in FIG. 1, conventional LCDs include two transparent panels, i.e., an upper panel  11  and a lower panel  10 , and a liquid crystal material  15  injected between the upper panel  11  and the lower panel  10 . The lower panel  10  includes a plurality of scan lines  24  and a plurality of data lines  23 . The scan lines  24  and data lines  23  are arranged in a matrix form wherein the scan lines  24  and the data lines  23  intersect each other. At each intersecting point between the scan lines  24  and the data lines  23 , a thin film transistor  21  (or “TFT”) and a pixel electrode  20  are provided. The TFT  21  comprises a gate electrode  25 , a source electrode  27  and a drain electrode  29 . Each gate electrode  25  is connected to one of the scan lines  24  and each source electrode  27  is connected to one of the data lines  23 . Each drain electrode  29  is connected to a respective pixel electrode  20 . Although not shown in FIG. 1, one end of each scan line  24  is connected to an output of a scan driving IC and one end of each data line  23  is connected to an output of a data driving IC. Additionally, the lower panel  10  can comprise a portion of a common line carrying a common signal applied from an outer device. 
     As shown in FIG. 1, the upper panel  11  comprises a common electrode  14  and a color filter  13 . There are three kinds of the color filters  13 , a red filter (R), a green filter (G) and a blue filter (B). Each of the color filters  13  is disposed at a position corresponding to the position of the pixel electrode  20  in the lower panel  10 . The common electrode  14  is formed on the color filter  13 . Generally, the common electrode  14  is made with one body covering one of the major surfaces of the upper panel  11 . Alternatively, the common electrode  14  comprises many bodies which are formed as strips arranged along with the scan lines  24  or the data lines  23 . 
     A molecule array direction of the liquid crystal material  15  injected between the upper panel  10  and the lower panel  11  is changed by the voltage difference between the pixel electrodes  20  and the common electrode  14 . When a scan voltage is applied to the scan lines  24 , the TFT  21  is turned on by the voltage applied to the gate electrode  25 . At that time, a data voltage applied to the data line  23  is sent to the drain electrode  29  from the source electrode  27  of the TFT  21  so that the data voltage is applied to the pixel electrode  20  which is connected to the drain electrode  29 . Consequently, a voltage difference is generated between the pixel electrode  20  and the common electrode  14 . As a result of the change of the molecule array direction of the liquid crystal material, the LCD functions as a display device. 
     FIGS. 2 a  and  2   b  show the conventional structure of the common electrode  14  in a liquid crystal display device. Referring to the FIGS. 2 a  and  2   b , the common pads  59   a  and  59   b  of the scan driver IC  55  and the data driver IC  56  apply a common voltage for the lower panel  10  to the common electrode  14  formed in the upper panel  11 . A silver dot  40  (or Ag dot) is disposed in each of the four corners of the lower panel  10  in contact with the common electrode  14  and and to the scan driver IC common pad  59   a  and the data driver IC common pad  59   b , so that the common voltage is applied to the common electrode  14  through the Ag dots  40 . 
     In the LCD according to the above-mentioned structure, the wave form of the common voltage which is detected at the portion of the common electrode  14  located near the Ag dot is different from the wave form of the common voltage which is detected at the portion of the common electrode  14  located spaced from the Ag dot. The difference in wave form is caused by a signal delay which occurs because the common voltage signal is delayed by the resistivity of the common electrode  14 . Therefore, it has been necessary to provide a third drive IC  57  for controlling the common electrode  14 . 
     In order to solve this problem without using a third drive circuit, U.S. Pat. No. 5,311,342 describes a structure, as shown in FIG. 3, in which an expanded common line  30  is formed continuously along two adjacent side portions of the matrix display portion of the LCD. The expanded common line  30  surrounds the matrix display portion by extending continuously from the scan pad part located at the lower left corner of the matrix portion in FIG. 3 to the data pad part located at the upper right corner of the matrix portion in FIG. 3 so that the scan pad part and the data pad part are connected each other. The common line  30  disposed in the lower panel  10  and the common electrode  14 , shown as a dashed-line square in FIG.  3  and disposed in the upper panel  11 , are connected to each other through the Ag dot  40 . Additionally, a conductive line  50  which is separately formed with the common line is connected to the common electrode  14  in order to reduce the time delay of the common voltage. 
     However, the structure described in U.S. Pat. No. 5,311,342 experiences problems caused by the expanded common line  30  which is continuously formed to extend from the scan driver IC common pad  59   a  located at the lower left corner of the matrix portion in FIG. 3 to the data driver IC common pad  59   b  located at the upper right corner of the matrix portion of FIG.  3 . Because of the common line  30  extending continuously between the data pad part and scan pad part, it is not possible to detect the exact amount of the delay time of the common voltage at the center of the display area. So, it is not possible to calculate the amount of the drop down voltage of the common voltage resulting from the time delay. Because such calculation of the drop down voltage is not possible, there is no way to compensate and correct for the drop down voltage. These problems result in flicker being generated in the image displayed by the device shown in FIG.  3  and also prevent uniformity of contrast and brightness in images displayed in the device of FIG.  3 . 
     SUMMARY OF THE INVENTION 
     The preferred embodiments of the present invention overcome the problems described above by providing an LCD which is adapted to allow for detection of the time delay or the distortion amount of the common voltage while eliminating the need for a third drive circuit which functions as a common drive circuit in the prior art. 
     The preferred embodiments of the present invention also provide an LCD which is arranged for allowing for calculation of an amount of distortion of the common voltage resulting from the time delay of the common voltage signal in the common line and common electrode and also facilitates compensation for such distortion of the common voltage applied to the common line. 
     According to one preferred embodiment of the present invention, a liquid crystal display substrate includes a first substrate having a plurality of pixel electrodes arranged in a matrix; a plurality of row pads and common electrode pads arranged on one side of two adjacent sides of said first substrate; a plurality of column pads and common electrode pads arranged on the other side of the two adjacent sides of said first substrate; a second substrate arranged to be opposite to said first substrate and to interpose a liquid crystal with said first substrate and having a common electrode for performing liquid crystal display by applying a voltage across said pixel electrodes and said common electrode; a single common line formed along only a single one of the two remaining sides of said first substrate so as to allow for measuring a voltage drop in a common voltage signal at a substantially central portion of said matrix; said common line being connected to at least one of said common electrode pad terminals to apply a common potential to said common electrode. 
     According to another preferred embodiment of the present invention, an LCD includes a lower panel having a plurality of scan lines and a plurality of data lines which are arranged in a matrix by intersecting each other; a pixel electrode disposed at each intersection point between the scan lines and data lines; a single common line which is disposed in the lower panel and extends along only one of four sides of an LCD display area including the pixel electrode so as to allow for measurement of a voltage drop occurring at a substantially central portion of said matrix; at least one connecting member disposed on said single common line; and an upper panel including a common electrode which is connected to the single common line via the at least one connecting member. 
     According to another preferred embodiment of the present invention, an LCD includes a lower panel having a plurality of scan lines and a plurality of data lines which are arranged in a matrix by intersecting each other; a pixel electrode disposed at each intersection point between the scan lines and data lines; a first common line and a second common line which are disposed in the lower panel surrounding a display area including the pixel electrode, the first common line and the second common line being spaced from each other so as to allow for measurement of a voltage drop occurring in a substantially central portion of the matrix; a plurality of connecting members disposed on the first common line and the second common line; and an upper panel including a common electrode which is connected to the first common line and the second common line through the plurality of connecting members. 
    
    
     Other features and advantages of the present invention will become apparent from the following description of the preferred embodiments of the present invention which are shown in the accompanying drawings. 
     BRIEF DESCRIPTION OF THE ATTACHED DRAWINGS 
     FIG. 1 is a perspective view showing the general structure of a conventional liquid crystal display device. 
     FIG. 2 a  is a plane view showing a common electrode, a driver IC common electrode and a silver dot in the conventional LCD device. 
     FIG. 2 b  is a cross-sectional view showing a common electrode, a driver IC common electrode and a silver dot in the conventional LCD device. 
     FIG. 3 is a plane view showing the structure of a conventional LCD. 
     FIG. 4 a  is a plane view showing a first preferred embodiment of the present invention including an LCD in a storage on common structure having only a single common line. 
     FIG. 4 b  is a cross-sectional view showing the first preferred embodiment of the present invention shown in FIG. 4 a.    
     FIG. 4 c  is a plan view showing a first preferred embodiment of the present invention an LCD in storage on gate structure having only a single common line. 
     FIG. 5 is a plane view showing a second preferred embodiment of the present invention including an LCD having only a single common line. 
     FIG. 6 is a plane view showing a third preferred embodiment of the present invention including an LCD having a first common line and a second common line which are separate from each other. 
     FIG. 7 is a plane view showing a fourth preferred embodiment of the present invention including an LCD having a first common line and a second common line which are separate from each other, and a static electricity protection circuit connecting the first and second common lines. 
     FIG. 8 is a plane view showing a fifth preferred embodiment of the present invention including an LCD having a first common line and a second common line which are separate from each other. 
     FIG. 9 is a plane view showing a sixth preferred embodiment of the present invention including an LCD having a first and a second common line which are separate from each other. 
     FIG. 10 is a plane view showing a seventh preferred embodiment of the present invention including an LCD having a first common line comprising two separate portions. 
     FIG. 11 is a plane view showing a eighth preferred embodiment of the present invention including an LCD having a second common line comprising two separate portions. 
     FIG. 12 is a plane view showing a ninth preferred embodiment of the present invention including an LCD having a first common line and a second common line comprising many different segments. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     A preferred embodiment of an LCD according to the present invention, as shown in FIG. 4 a , includes a plurality of scan lines  124 , a plurality of data lines  123 , and a display area having a pixel electrode  220  and a thin film transistor  121  at each intersection area of the scan lines  124  and data lines  123  and a common electrode  114 , shown as a dashed-line square. This preferred embodiment further includes a single common line  100  disposed at the outer portion of the display area in parallel with the scan lines  124 . As seen in FIG. 4 a , the single common line  100  is disposed in the lower side of the display area and is connected to a first common pad  210   a  located at the lower left corner of the display area. In addition, a first connecting member  130 , preferably in the form of a silver dot, is disposed at one position along the single common line  100 . A second common pad  210   b  is located at the upper right corner of the display area but is not connected to the single common line  100 . A second connecting member  131 , in the form of a silver dot, may be provided at a location of the second common pad  210   b . As seen in FIG. 4 b , the common line disposed on the lower plate  112   100  connects the common electrode  114  disposed on the upper plate  111  through the silver dots  130  and  131 . 
     The single common line  100  extends from an area near the first connecting member  130  at the lower left corner along a bottom side of the display area to the lower right corner thereof where another first connecting member  130  is located. Any number of connecting members  130  can be disposed along the single common line  100  to reduce distortion of the voltage signal. The single common line  100  does not extend along the right side of the display area as seen in FIG. 4 a.    
     A common electrode  114  is disposed in the upper panel similar to the common electrode  14  in the prior art. The common electrode  114  is connected to the single common line  100  via the first connecting member  130  in the lower left corner of the display area. The common electrode  114  is also connected to the first common pad  210   a  and the second common pad  210   b  so as to apply a common voltage. The common electrode  114  may also be preferably connected to the conductive line  120  provided to reduce the delay time of the input common voltage signal. 
     Before the LCD is assembled into a final product, a common voltage is applied to the single common line  100  through the first common pad  210   a . Then, the common voltage is applied to the common electrode  114  and is then finally applied to the second common pad  210   b  through the second connecting member  131 . 
     As seen in FIG. 4 a , with the structure and arrangement of the single common line  100 , the single common line  100  does not extend along the right side of the display area and is not extended to the second common pad  210   b  located at the upper right corner of the display area. As a result of such arrangement, a wave form of the common voltage applied to the second common pad  210   b  can be calculated because the second common pad  210   b  is not connected to the first common pad  210   a  as in the prior art in which the common line extends continuously between the first and second common pads and connects the common pads to each other thereby preventing any detection of input common voltage and output common voltage. Therefore, using the first common pad  210   a  to detect input common voltage and the second common pad  210   b  to detect output common voltage with the preferred embodiment of the present invention shown in FIG. 4, the distortion of the common voltage wave form or amount of the drop down voltage of the common voltage occurring in the central portion of the display area can be calculated exactly. Thus, a device for compensating for the detected and calculated precise amount of distortion of the common voltage can be connected to the conductive line  120  and adapted to supply a correction amount of voltage to compensate for the common voltage distortion. 
     Thus, the single common line  100  shown in FIG. 4 a  provides significant advantages over the prior art device shown in FIG. 3 in that, in addition to eliminating the need for a third drive circuit which in the prior art functioned as a common drive circuit, the single common line  100  allows for detection of an applied common voltage at the first common pad  210   a  and an output common voltage at the second common pad  210   b  and allows a difference between the applied and output common voltages to be calculated which enables elimination of the distortion of the common voltage by applying a compensating voltage to the common electrode  114  via the conductive line  120  connected to the common electrode  114 . Because such voltage distortion can be accurately and easily corrected, the LCD incorporating the single common line  100  having the structure and arrangement shown in FIG. 4 significantly reduces flicker and achieves uniformity of the display contrast and brightness. 
     In this preferred embodiment, as seen in FIG. 4 a , an LCD in which the storage capacitance has a storage on common structure is disclosed. This preferred embodiment can also be applied to another arrangement of the storage capacitance which is the storage on gate structure. FIG. 4 c  shows an LCD panel having the single common line  100  in a storage on gate structure. 
     Additional preferred embodiments of the present invention are shown in FIGS. 5-12, which are described below. It should be noted that each of the preferred embodiments shown in FIGS. 5-12 achieve the same advantages as described above with reference to the preferred embodiment shown in FIG. 4 a . Furthermore, these additional preferred embodiments can be adapted to either the storage on common structure or the storage on gate structure of the LCD. In the following description of the additional preferred embodiments, only the storage on common structure will be discussed and illustrated in the corresponding Figures although it should be understood that each of these additional preferred embodiments can also be adapted to the storage on gate structure. 
     A second preferred embodiment is shown in FIG.  5 . The second preferred embodiment also includes only a single common line. However, for the purposes of clarity of the description of the present preferred embodiment and those preferred embodiments shown in FIGS. 6-12, the single common line  100  shown in FIG. 4 will be referred to as a first common line  100  and the single common line  110  shown in FIG. 5 will be hereinafter referred to as a second common line  110 . 
     The difference between the first common line  100  of the first preferred embodiment shown in FIG. 4 a  and the second common line  110  of the second preferred embodiment shown in FIG. 5 is that the second common line  110  is located at the right side of the display area and is connected to the second common pad  210   b . The second common pad  210   b  includes a plurality of connecting members  131  disposed therealong. 
     As seen in FIG. 5, the second common line  110  extends from the second common pad  210   b  along the right side of the display area but does not extend to a bottom side of the display area. The first common pad  210   a  includes a single first connecting member  130  and does not extend along the bottom side of the display area as in the first preferred embodiment shown in FIG. 4 a.    
     As with the second preferred embodiment shown in FIG. 5, the first common pad  210   a  can be used to detect an input common voltage and the second common pad  210   b  can be used to detect the output common voltage so that the distortion amount of the common voltage in a central portion of the display area can be calculated and compensated for as described above. 
     It should be noted that the single common line preferred embodiments shown in FIGS. 4 a - 4   c  and  5  are preferred compared to the preferred embodiments shown in FIGS. 6-12 because the preferred embodiments containing only a single common line provide more accurate and reliable calculation of voltage drop. 
     Another preferred embodiment is shown in FIG.  6 . As seen in FIG. 6, the first common line  100  is located at a bottom side of the display area. This preferred embodiment also preferably includes a second common line  110  disposed at the outer portion of the display area in parallel with the data lines  123 . The second common line  110  is formed along the right side of the display area shown in FIG.  6 . 
     As seen in FIG. 6, the first common line  100  and the second common line  110  are separate from each other and not continuously formed. The separation between the first common line  100  and the second common line  110  is seen in FIG. 6 in the lower right corner of the display area in the form of a space between the two common lines  100 ,  110 . This space must be provided so that the first common line  100  and the second common line  110  are not continuously formed or connected so as to allow for measurement of a voltage drop occurring in the substantially central portion of the display area. As a result of the structure and arrangement of the first common line  100  and the second common line  110 , the applied or input voltage at the first common pad  210   a , located at the lower left corner of the display area, can be measured and the resulting or output voltage which is output at the second common pad  210   b  located at the upper right corner of the display area can be measured. A difference between the two measured voltages provides an accurate measurement of the voltage drop occurring in the substantially central portion of the display area. This voltage drop can be compensated for as described above. 
     As seen in FIG.  6  and as is true with the preferred embodiments of the present invention shown in FIGS. 4 a - 12 , a common electrode  114  is preferably disposed in the upper panel similar to the common electrode  14  in the prior art. The common electrode  114  is connected to the first common line  100  via the first connecting member  130  in the lower left corner of the display area and to the second connecting member  131  in the upper right corner. This preferred embodiment can still further comprise a conductive line  120  which is connected to the common electrode  114  and performs the function described above with reference to the first preferred embodiment. 
     Another preferred embodiment, which is derived from the preferred embodiment shown in FIG. 6, is shown in FIG.  7 . In addition to the structure and arrangement of the first common line  100  and the second common line  110 , the second preferred embodiment shown in FIG. 7 further comprises a static electricity protection circuit  200  which connects the first common line  100  with the second common line  110 , as shown in FIG.  7 . The static electricity protection circuit  200  electrically connects the first common line  100  with the second common line  110  only when a high voltage difference occurs between the lines  100 ,  110 . In a normal state, i.e., when there is a low voltage difference between the first common line  100  and the second common line  110  or when there is not any static electricity therebetween, the first common line  100  and the second common line  110  are electrically isolated. 
     In a further preferred embodiment shown in FIG. 8, the arrangement and structure of the first common line  100  and the second common line  110  is varied as compared to the preferred embodiment shown in FIG.  6 . In the preferred embodiment shown in FIG. 8, the area occupied by the second common line  110  is reduced and the area occupied by the first common line  100  is increased such that the first common line  100  extends completely along the bottom side of the display area and along a portion of the right side of the display area. However, the first and second common lines  100 ,  110  are not connected but instead are still separated by a space to allow for the input common voltage to be measured at the first common pad  210   a  and the output common voltage to be measured at the second common pad  210   b  to calculate a precise amount of common voltage distortion occurring in the central portion of the display area. 
     Alternatively, in the preferred embodiment shown in FIG. 9, the area occupied by the second common line  110  can be expanded and the area occupied by the first common line  100  can be reduced as shown in FIG.  9 . Thus, in the preferred embodiment shown in FIG. 9, the first common line  100  extends along only a portion of the bottom side of the display area and the second common line  110  extends along the right side of the display area and down along a portion of the bottom side of the display area. However, the first and second common lines  100 ,  110  are not connected but instead are still separated by a space to allow for the input common voltage to be measured at the first common pad  210   a  and the output common voltage to be measured at the second common pad  210   b  to calculate a precise amount of common voltage distortion occurring in the substantially central portion of the display area. 
     Thus, it is clear from FIGS. 8 and 9 that the shape of the first common line  100  and the second common line  110  can be formed as desired as long as the first common line  100  is separate from and not continuously formed with or connected to the second common line  110  to allow the voltage drop to be accurately calculated and compensated for as described above. 
     In still another preferred embodiment of the present invention, the first common line  100  of the preferred embodiment can comprise at least two separate and independent segments, as shown in FIG.  10 . Alternatively, the second common line  110  can comprise at least two separate and independent segments, as shown in FIG.  11 . Even though not shown in figures, the first common line  100  and the second common line  110  can comprise at least two separate and independent segments. 
     Still alternatively, the first common line  100  and the second common line  110  of another preferred embodiment can comprise a plurality of separate and independent segments, as shown in FIG.  12 . Although not shown in FIG. 12, only one of the first common line  100  and the second common line  110  may comprise a plurality of separate and independent segments while the other of the first common line  100  and the second common line  110  may comprise a single independent segment. 
     As described above, the LCD according to the preferred embodiments of the present invention has a single common line or has independent, spaced first and second common lines, each of which common lines includes a first terminal for applying a common voltage and another terminal, possibly provided on the second common line, including a second terminal for detecting the common voltage. As a result of the structure and arrangement of the single common line or the independently formed and spaced first and second common lines, the input and output common voltages can be accurately detected and the difference therebetween can be precisely calculated to allow for a compensating voltage to be applied to correct for the voltage distortion experienced in the substantially central portion of the display area. Therefore, the preferred embodiments of the present invention eliminate the need for a third drive circuit used in prior art devices and also eliminate the distortion of the common voltage by allowing for calculation and applying of a compensating voltage to the common electrode via the conductive line connected to the common electrode. As a result, the preferred embodiments of the present invention reduce flicker and achieve uniformity of the display quality, such as contrast and brightness. 
     Although the present invention has been described in relation to preferred embodiments thereof, many variations and modifications and other uses will become apparent to those skilled in the art. It is preferred, therefore, that the present invention be limited not by the specific disclosure herein, but only by the appended claims.