Patent Publication Number: US-2007103827-A1

Title: Liquid crystal display having electrostatic discharge unit

Description:
FIELD OF THE INVENTION  
      The present invention relates to liquid crystal displays, and particularly to a liquid crystal display (LCD) having an electrostatic discharge unit.  
     BACKGROUND  
      An LCD has the advantages of portability, low power consumption, and low radiation, and has been widely used in various portable information products such as notebooks, personal digital assistants (PDAs), video cameras and the like. Furthermore, the LCD is considered by many to have the potential to completely replace cathode ray tube (CRT) monitors and televisions.  
      During an LCD fabricating process, electrostatic charge may be generated in the LCD. If too much electrical charge builds up at any one location on the LCD, the built up electrical charge is liable to discharge, thereby damaging or destroying a driving integrated circuit (IC) of the LCD such as a gate IC or a data IC. Thus in a typical LCD, a plurality of electrostatic discharge units are employed. The electrostatic discharge units discharge any electrical charge in a timely manner during the fabricating process.  
       FIG. 4  is a schematic, abbreviated diagram of a layout of certain parts of a typical LCD. The LCD  10  includes a thin film transistor (TFT) substrate  2 , a driving IC  3  disposed on a surface of the TFT substrate  2 , a plurality of first conducting lines  6  disposed on the TFT substrate  2 , and a flexible printed circuit board (FPCB)  4 . The FPCB  4  includes a plurality of second conducting lines  43  (only one shown), an electrostatic discharge unit  45  formed thereon, and a system controlling circuit  47  formed thereon. Each of the first conducting lines  6  includes a first metal pad (not shown) connected to a corresponding input/output pin  31  of the driving IC  3 , and a second metal pad (not shown) at an edge of the TFT substrate  2 . Each of the second conducting lines  43  includes a third metal pad  41  connected to a corresponding one of the second metal pads. A first terminal of the electrostatic discharge unit  45  is connected to the driving IC  3  via one of the second conducting lines  43  and a corresponding first conducting line  6  in series. A second terminal of the electrostatic discharge unit  45  is connected to ground. A third terminal of the electrostatic discharge unit  45  is connected to the system controlling circuit  47 . The system controlling circuit  47  is used to control the electrostatic discharge unit  45  in order to discharge electrostatic charge of the driving IC  3 .  
      However, the electrostatic discharge unit  45  is positioned on the FPCB  4  and the driving IC  3  is positioned on the surface of the TFT substrate  2 . An electrical discharge path formed by the driving IC  3 , the first conducting line  6 , the third metal pad  41 , the second conducting line  43  and the electrostatic discharge unit  45  to ground is very long. Therefore, the electrostatic charge of the driving IC  3  may not be completely discharged to ground.  
      It is desired to provide an LCD which overcomes the above-described deficiencies.  
     SUMMARY  
      In one preferred embodiment, an LCD includes a TFT substrate, a driving IC disposed on the TFT substrate, a FPCB connected to an edge of the TFT substrate, at least one electrostatic discharge unit provided on the TFT substrate, and a system controlling circuit. The TFT substrate includes a plurality of first conducting lines. Each first conducting line includes a first metal pads and a second metal pad at two opposite ends thereof respectively. The driving IC includes a plurality of input/output pins connected to the first metal pads respectively. The FPCB includes a plurality of second conducting lines connected to the first conducting lines via the second metal pads respectively. The at least one electrostatic discharge unit is located and electrically connected between one of the first metal pads and one of the second metal pads with the electrical connection being via a corresponding one of the first conducting lines, a terminal of the at least one electrostatic discharge unit is connected to ground for discharging any electrostatic charge of the driving IC. The system controlling circuit is connected to the driving IC via one of the second conducting lines, the corresponding first conducting line, and the at least one electrostatic discharge unit in series.  
      Advantages and novel features of the above-described LCD will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings, in which:  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a schematic, abbreviated diagram of a layout of certain parts of an LCD according to a first embodiment of the present invention, the LCD including a driving IC and an electrostatic discharge unit;  
       FIG. 2  is a circuit diagram of an electrical discharge path of  FIG. 1 , including details of the electrostatic discharge unit;  
       FIG. 3  is a schematic, abbreviated diagram of a layout of certain parts of an LCD according to a second embodiment of the present invention; and  
       FIG. 4  is a schematic, abbreviated diagram of a layout of certain parts of a conventional LCD. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       FIG. 1  is a schematic, abbreviated diagram of a layout of certain parts of an LCD according to a first embodiment of the present invention. The LCD  100  includes a TFT substrate  12 , a driving IC  13  disposed on a surface of the TFT substrate  12 , an electrostatic discharge unit  15  formed on the surface of the TFT substrate  12 , a plurality of first conducting lines  16  disposed on the TFT substrate  12 , and an FPCB  14 . The FPCB  14  includes a plurality of second conducting lines  143  (only one shown), and a system controlling circuit  147  formed thereon. Each of the first conducting lines  16  includes a first metal pad (not shown) connected to a corresponding input/output pin  131  of the driving IC  13 , and a second metal pad (not shown) at an edge of the TFT substrate  12 . Each of the second conducting lines  143  includes a third metal pad  141  connected to a corresponding one of the second metal pads. The electrostatic discharge unit  15  is located and electrically connected between one of the first metal pads and one of the second metal pads, with the electrical connection being via a corresponding one of the first conducting lines  16 . A terminal of the electrostatic discharge unit  15  is connected to ground or a power pin of the driving IC  13 , for discharging any electrostatic charge of the driving IC  13 . In the illustrated embodiment, this terminal of the electrostatic discharge unit  15  is connected to ground. The system controlling circuit  147  is connected to the driving IC  13  via at least one of the second conducting lines  143 , the electrostatic discharge unit  15 , and said corresponding first conducting line  16  in series. The system controlling circuit  147  is used to control the driving IC  13 .  
      The electrostatic discharge unit  15  and the driving IC  13  are both formed on the surface of the TFT substrate  12 . An electrical discharge path formed by the driving IC  13 , said corresponding first conducting line  16 , and the electrostatic discharge unit  15  to ground (or to the power pin of the driving IC  13 ) is relatively short in length. Therefore the electrostatic charge of the driving IC  13  can be completely discharged to ground (or to the power pin of the driving IC  13 ).  
       FIG. 2  is a circuit diagram of the electrical discharge path of the LCD  100 , including details of the electrostatic discharge unit  15 . The electrostatic discharge unit  15  includes a capacitor  153 , and two diodes  151 ,  152 . The positive terminals of the two diodes  151 ,  152  are connected to ground (or to the power pin of the driving IC  13 ), for discharging any electrostatic charge of the driving IC  13 . In the illustrated embodiment, these positive terminals are connected to ground. The negative terminals of the two diodes  151 ,  152  are connected to the corresponding input/output pin  131  of the driving IC  13  via said corresponding conducting line  16 . The capacitor  153  is connected between the two negative terminals of the two diodes  151 ,  152 .  
       FIG. 3  is a schematic, abbreviated diagram of a layout of certain parts of an LCD according to a second embodiment of the present invention. The LCD  200  includes a thin film transistor (TFT) substrate  22 , an FPCB  24  connected to an edge of the substrate  22 , a driving IC  23  formed on a surface of the FPCB  24 , an electrostatic discharge unit  25  formed on the surface of the FPCB  24 , and a system controlling circuit  247  formed on the surface of the FPCB  24 . The FPCB  24  includes a plurality of conducting lines  26 . Each of the conducting lines  26  includes a first metal pad  241  at an end of the FPCB  24  that is connected to the TFT substrate  22 , and a second metal pad (not shown) at an end of the conducting line  26  that is distal from the TFT substrate  22 . The driving IC  23  includes a plurality of input/output pins  231 . The input/output pins  231  of the driving IC  23  are connected to the second metal pads respectively. The electrostatic discharge unit  25  is located and electrically connected between one of the first metal pads  241  and a corresponding one of the second metal pads, with the electrical connection being via a corresponding one of the conducting lines  26 . A terminal of the electrostatic discharge unit  25  is connected to ground or to a power pin of the driving IC  23 , for discharging any electrostatic charge of the driving IC  23 . In the illustrated embodiment, this terminal of the electrostatic discharge unit  25  is connected to ground. The system controlling circuit  247  is connected to the driving IC  23  via a conducting line (not labeled) connecting to the electrostatic discharge unit  25 , the electrostatic discharge unit  25 , and said corresponding first conducting line  26  in series. The system controlling circuit  247  is used to control the driving IC  23 .  
      The electrostatic discharge unit  25  and the driving IC  23  are both formed on the surface of the FPCB  24 . An electrical discharge path formed by the driving IC  23 , said corresponding first conducting line  26 , and the electrostatic discharge unit  25  to ground (or to the power pin of the driving IC  23 ) is relatively short in length. Therefore the electrostatic charge of the driving IC  23  can be completely discharged to ground (or to the power pin of the driving IC  23 ).  
      In an alternative embodiment, more than one of the input/output pins  131  of the driving IC  13  can also be connected to corresponding plural electrostatic discharge units  15  respectively. In another words, the LCD  100  can include a plurality of electrostatic discharge units  15 , each of which is connected between a respective one of the input/output pins of the driving IC  13  and ground (or the power pin of the driving IC  13 ). Furthermore, the system controlling circuit  147  can instead be formed on the surface of the TFT substrate  12 .  
      It is to be understood, however, that even though numerous characteristics and advantages of preferred embodiments have been set out in the foregoing description, together with details of the structures and functions of the embodiments, the disclosure is illustrative only; and that changes may be made in detail, especially in matters of shape, size, and arrangement of parts within the principles of present invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.