Patent Document

CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]     This application is a continuation-in-part of U.S. patent application Ser. No. 11/042,034, filed Jan. 25, 2005, the contents of which are incorporated by reference herein. 
     
    
     BACKGROUND  
       [0002]     1. Field of Invention  
         [0003]     The present invention relates to a protection circuit with transistors. More particularly, the present invention relates to a display apparatus current discharging method and a display apparatus current leakage reducing method.  
         [0004]     2. Description of Related Art  
         [0005]     Flat panel displays are mostly made of insulating glass substrates, where electrostatic discharge (ESD) is easily induced to damage components thereof, greatly decreasing the manufacturing yield of the flat panel displays. Typically, protection circuits for preventing ESD are configured on display panels to achieve the protection of components.  
         [0006]      FIG. 1  is a schematic view of a flat panel display with conventional protection circuits. As illustrated in  FIG. 1 , a display panel  100  has a plurality of scan lines  102  and a plurality of data lines  104 . A plurality of display units  106  are provided at intersections of the scan lines  102  and the data lines  104 . Protection circuits  112  are electrically connected between a discharging line  110  and one of the scan lines  102  or the data lines  104 . When a discharging pulse is generated on the scan line  102  or the data line  104  due to the ESD of the display panel  100 , the protection circuits  112  can disperse the discharging pulse to the discharging line  110  and thus prevent the display units  106  or other components from being damaged by the discharging pulse.  
         [0007]     For the protection circuits, particularly the protection circuits for ESD used in the flat panel displays, the prior art provides several different implementations.  FIG. 2A  is a schematic view of a conventional protection circuit. As illustrated in  FIG. 2A , two transistors  222   a  and  224   a  are electrically connected in parallel between the scan line  102  and the discharging line  110 . When a drain and a gate of the transistor are short-circuited, the transistor is equivalent to a diode.  FIG. 2B  is an equivalent circuit diagram of the protection circuit  112   a  of  FIG. 2A . The two equivalent diodes  222   b  and  224   b  are opposite to each other, and therefore are able to deal with discharging currents either from the scan line  102  to the discharging line  110  or from the discharging line  110  to the scan line  102 .  
         [0008]     U.S. Pat. No. 5,744,837 discloses another protection circuit, as illustrated in  FIG. 3A . A protection circuit  112   b  comprises four transistors  322   a ,  324   a ,  326   a  and  328   a  electrically connected between the scan line  102  and the discharging line  110 . A drain and a gate of each of the transistors  322   a ,  324   a ,  326   a  and  328   a  are individually short-circuited.  FIG. 3B  is an equivalent circuit diagram of the protection circuit  112   b  of  FIG. 3A . The equivalent diodes  322   b  and  324   b  are opposite to the equivalent diodes  326   b  and  328   b , and therefore, they are able to deal with discharging currents either from the scan line  102  to the discharging line  110  or from the discharging line  110  to the scan line  102 .  
         [0009]     U.S. Pat. No. 5,606,340 discloses another protection circuit, as illustrated in  FIG. 4A . A protection circuit  112   c  comprises four transistors  422   a ,  424   a ,  426   a  and  428   a  electrically connected between the scan line  102  and the discharging line  110 . A drain and a gate of each of the transistors  422   a ,  424   a ,  426   a  and  428   a  are individually short-circuited.  FIG. 4B  is an equivalent circuit diagram of the protection circuit  112   c  of  FIG. 4A . As illustrated in  FIG. 4B , the transistors  422   a  and  424   a  are equivalent to a switching element  422   b , and ON/OFF states of the switching element  422   b  are controlled by the equivalent diodes  426   b  and  428   b . When a potential difference between the scan line  102  and the discharging line  110  is great enough, the diodes  426   b  and  428   b  switch on the switching element  422   b , such that the discharging currents are dispersed to the scan line  102  or the discharging line  110 , which has a lower potential via the switching element  422   b  (i.e. the transistors  422   a  and  424   a ).  
         [0010]     However, the foregoing conventional protection circuits have drawbacks such as large leakage currents, small discharging currents, slow discharging speed and easy disablements due to being damaged during manufacturing. In the flat panel display, a larger size or higher resolution indicates that the quantity of the contained scan lines and data lines are greater. If the leakage current of each protection circuit electrically connected to the corresponding scan line and data line is large, the total leakage current of the whole display panel becomes serious and causes tremendous power consumption. The power stored in a portable electronic device is finite. For example, the operating voltages of the in-plane switching (IPS) mode used in liquid crystal displays (LCDs) are higher than for average devices, so the leakage currents thereof are greater. In conclusion, these drawbacks are very disadvantageous to portable electronic devices and the IPS modes often used in LCD TVs.  
       SUMMARY  
       [0011]     It is therefore an objective of the present invention to provide a protection circuit, which can reduce leakage currents, enlarge discharging currents, hasten discharging speed and avoid being easily disabled due to damage during manufacturing.  
         [0012]     It is another objective of the present invention to provide a display device, which has lower leakage current and better protection from ESD.  
         [0013]     In accordance with the foregoing and other objectives of the present invention, a display device and a protection circuit thereof are provided. The display device has a display array, a discharging line and a plurality of protection circuits. The display array has a plurality of scan lines, a plurality of data lines and a plurality of display units, and the display units are provided at intersections of the scan lines and the data lines. The discharging line surrounds the display array, and the protection circuits are electrically connected between the discharging line and the scan lines or the data lines.  
         [0014]     Each of the protection circuits has a first discharging circuit, a second discharging circuit. The first discharging circuit has a first switching element, a resistance element and a second switching element electrically connected in series between the discharging line and one of the scan lines or the data lines to which the protection circuit is electrically connected. The resistance element controls the switch states of the second switching element. The second discharging circuit has a third switching element, the resistance element and a fourth switching element electrically connected in series between the discharging line and the one of the scan lines or the data lines to which the protection circuit is electrically connected. The resistance element controls the switch states of the third switching element, and the second and third switching elements are electrically connected.  
         [0015]     According to one preferred embodiment of the present invention, a current direction of the first discharging circuit is opposite to a current direction of the second discharging circuit. When the second and third switching elements are switched on, the scan line or the data line discharges to the discharging line via the second and third switching elements. A gate and a drain of the first switching element are electrically connected to the scan line or the data line, and a gate and a drain of the fourth switching element are electrically connected to the discharging line. A gate of the second switching element is electrically connected to a gate of the third switching element, a drain of the second switching element is electrically connected to a drain of the third switching element, and the resistance element is connected between the gate and the drain of the second switching element.  
         [0016]     A W/L of the second switching element is greater than a W/L of the first switching element, and a W/L of the third switching element is greater than a W/L of the fourth switching element. The W/L of the second switching element is equal to the W/L of the third switching element, and the W/L of the fourth switching element is equal to the W/L of the first switching element. A material of the resistance element is indium-tin oxide or amorphous silicon. Alternatively, the resistance element is a thin film transistor or a diode.  
         [0017]     The protection circuit reduces the leakage currents of the first and second switching elements in the OFF states by the resistance element. Moreover, when the first and second switching elements are switched on by the great potential difference, the voltage drop of the resistance element sequentially switches on the second and third switching elements, so as to provide an additional discharging path between the discharging line and the scan line or the data line, thus enlarging the discharging currents and hastening the discharging speed. In addition, two separate discharging paths, i.e. the original discharging path and the additional discharging path, ensure that the protection circuit is not disabled due to damage during manufacturing, thus improving the reliability.  
         [0018]     According to another embodiment, a display apparatus current discharging method comprises the steps of: A display apparatus current discharging method, comprising steps of: providing a potential difference between a first line and a second line; switching on a first switching element; generating a voltage drop of a resistance element having a first end and a second end; switching on a second switching element; providing a first discharging path through the first line, the first switching element, the resistance element, the second switching element, and the second line; and discharging a first current via the first discharging path.  
         [0019]     According to another embodiment, a display apparatus current leakage reducing method comprises providing a potential difference between a first line and a second line; switching off a first switching element and a second switching element; providing a leakage path through the first line, a resistance element having a first end and a second end, and the second line; and reducing a leakage through the leakage path by the resistance element.  
         [0020]     It is to be understood that both the foregoing general description and the following detailed description are examples and are intended to provide further explanation of the invention as claimed. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0021]     These and other features, aspects, and advantages of the present invention will become better understood with regard to the following description, appended claims, and accompanying drawings where:  
         [0022]      FIG. 1  is a schematic view of a flat panel display with conventional protection circuits;  
         [0023]      FIG. 2A  is a schematic view of a conventional protection circuit;  
         [0024]      FIG. 2B  is an equivalent circuit diagram of the protection circuit of  FIG. 2A ;  
         [0025]      FIG. 3A  is a schematic view of another conventional protection circuit;  
         [0026]      FIG. 3B  is an equivalent circuit diagram of the protection circuit of  FIG. 3A ;  
         [0027]      FIG. 4A  is a schematic view of another conventional protection circuit;  
         [0028]      FIG. 4B  is an equivalent circuit diagram of the protection circuit of  FIG. 4A ;  
         [0029]      FIG. 5A  is a schematic view of a display device of one preferred embodiment in the present invention;  
         [0030]      FIG. 5B  is a schematic view of a protection circuit of one preferred embodiment in the present invention; and  
         [0031]      FIG. 5C  is a schematic view of a protection circuit of another embodiment in the present invention.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0032]     Reference will now be made in detail to the present preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts.  
         [0033]      FIG. 5A  is a schematic view of a display device of one preferred embodiment in the present invention. As illustrated in  FIG. 5A , the display device has a display array  500 , a discharging line  510  and a plurality of protection circuits  512 . The display array  500  has a plurality of scan lines  502 , a plurality of data lines  504  and a plurality of display units  506 . The display units  506  are provided at intersections of the scan lines  502  and the data lines  504 . The discharging line  510  surrounds the display array  500 , and the protection circuits  512  are electrically connected between the discharging line  510  and the scan lines  502  or the data lines  504 . For example, when the display device is a liquid crystal display, a display unit  506  thereof is a liquid crystal cell comprising at least one thin film transistor.  
         [0034]      FIG. 5B  is a schematic view of a protection circuit of one preferred embodiment in the present invention. For clarity, in the embodiment, a protection circuit  512   a  is electrically connected between the scan line  502  and the discharging line  510 . However, the protection circuit  512   a  can also be connected between the data line  504  and the discharging line  510  to protect components on the data line  504 .  
         [0035]     As illustrated in  FIG. 5B , each of the protection circuits  512   a  has a first discharging circuit and a second discharging circuit. The first discharging circuit has a first transistor  522 , a resistance element  532  and a second transistor  524  electrically connected in series between the scan line  502  and the discharging line  510 . A gate and a drain of the first transistor  522  are electrically connected. The second discharging circuit has a third transistor  526 , the resistance element  532 , and a fourth transistor  528  electrically connected in series between the scan line  502  and the discharging line  510 . A gate and a drain of the fourth transistor  528  are electrically connected. Therefore, a current direction of the first discharging circuit is opposite to a current direction of the second discharging circuit.  
         [0036]     Moreover, a gate of the second transistor  524  is electrically connected to a gate of the third transistor  526 . A first electrode of the second transistor  524  is electrically connected to the scan line  502 . A second electrode of the second transistor  524  is electrically connected to a first electrode  525  of the third transistor  526 . In addition, the resistance element  532  is electrically connected between the gates and the second electrodes of the two transistors  524  and  526 , and therefore the switch states of the second transistor  524  and the third transistor  526  can be controlled by the voltage drop on the resistance element  532 .  
         [0037]     According to the circuit configuration, the protection circuit  512   a  has two different current conditions in response to normal operation and the discharging operation. The following descriptions interpret the two different current conditions, separately.  
         [0038]     When the protection circuit  512   a  is operated normally, where the potential difference between the scan line  502  and the discharging line  510  does not exceed a voltage tolerance, the current passes through the first transistor  522 , the resistance element  532  and the second transistor  524 , and through the fourth transistor  528 , the resistance element  532  and the third transistor  526 . Thus, the protection circuit  512   a  can reduce the leakage currents of the first and second discharging circuits by the resistance element  532 . At the same time, the first electrode  525  of the third transistor  526  is used as a source thereof, and therefore an additional discharging path comprising the third transistor  526  and the second transistor  524  is in an OFF state. In other words, when the protection circuit  512   a  is normally operated, there is no discharging current generated between the scan line  502  and the discharging line  510 .  
         [0039]     When discharging is induced, where the potential difference between the scan line  502  and the discharging line  510  exceeds the voltage tolerance, one of the first and fourth transistors  522  and  528  is switched on by a forward potential difference between the scan line  502  and the discharging line  510 . Moreover, at the same time, the voltage drop of the resistance element  532  sequentially switches on the second transistor  524  and the third transistor  526 , and an additional discharging path is thus provided between the scan line  502  and the discharging line  510  for enlarging discharging currents and hastening discharging speed. In addition, the two separate discharging paths ensure that the protection circuit is not disabled due to damage during manufacturing, improving the reliability.  
         [0040]     It is noticed that, during discharging, the first electrode  525  of the third transistor  526  is used as a drain of the same, and a first electrode of the second transistor  524  is used as a source of the same. That is, the drains and the sources of the second transistor  524  and the third transistor  526  are not limited, and the first electrodes and the second electrodes of both transistors can be sources or drains with respect to different conditions.  
         [0041]     According to the preferred embodiment, the resistance value of the resistance element  532  is about 70 MΩ, and the material thereof can be indium-tin oxide or amorphous silicon. Alternatively, the resistance element  532  can be a thin film transistor or a diode. Some designations are determined for clear description, the channel width of a transistor is designated as W, and the channel length of the transistor is designated as L. A W/L of the first transistor  522  and a W/L of the fourth transistor  528  are both 10/15, and a W/L of the second transistor  524  and a W/L of the third transistor are both 45/5.25. In other words, the W/L of the second transistor  524  is greater than the WIL of the first transistor  522 , and the W/L of the third transistor  526  is greater than the W/L of the fourth transistor  528 .  
         [0042]     When the protection circuit  512   a  of the preferred embodiment is configured in a conventional twisted nematic (TN) liquid crystal display, the leakage current is one quarter of the leakage current of the protection circuit  112   b  illustrated in  FIG. 3A  under the potential difference of about 5V. Compared to the protection circuit  112   a  illustrated in  FIG. 2A , the leakage current of the protection circuit  512   a  is decreased more than one order. Furthermore, when the protection circuit  512   a  of the preferred embodiment is configured in an IPS liquid crystal display, the leakage current is one-fifth of the leakage current of the protection circuit  112   b  illustrated in  FIG. 3A  under the potential difference of about 7V, and is one-seventh of the protection circuit  112   a  illustrated in  FIG. 2A .  
         [0043]      FIG. 5C  is a schematic view of a protection circuit of another embodiment in the present invention. As illustrated in  FIG. 5C , the protection circuit  512   b  further comprises at least one fifth transistor  534 , which is electrically connected between the resistance element  532  and the first transistor  522 . A sixth transistor  535  can also be electrically connected between the resistance element  532  and the fourth transistor  528 . The fifth transistor  534  and the sixth transistor  535  are used in conjunction with the first transistor  522  and the fourth transistor  528  for adjusting the summed and effective W/L. The fifth transistor  534  or the sixth transistor  535  can also be a resistance element. That is, the fifth transistor  534  and the sixth transistor  535  can be used in conjunction with the resistance element  532  for separately optimizing the individual resistance of the first discharging circuit and the second discharging circuit.  
         [0044]     In one aspect, the foregoing embodiments also disclose a display apparatus current discharging method. A potential difference is provided between the scan line  502  and the discharging line  510 . The first transistor  522  is switched on, and a voltage drop of a resistance element  532  is generated. The resistance element  532  has a first end and a second end. The second transistor  524  is then switched on, and a first discharging path through the scan line  502 , the first transistor  522 , the resistance element  532 , the second transistor  524 , and the discharging line  510  is provided. Thus, a first current is discharged via the first discharging path as stated above.  
         [0045]     More particularly, a first electrode of the first transistor  522  is electrically connected to the scan line  502 . A second electrode of the first  522  is electrically connected to the first end of the resistance element  532 . A gate electrode of the first transistor  522  is electrically connected to the scan line  502 . A first electrode of the second transistor  524  is electrically connected to the discharging line  510 . A second electrode of the second transistor  524  is electrically connected to the second end of the resistance element  532 . A gate electrode of the second transistor  524  is electrically connected to the first end of the resistance element  532 . In the embodiment, a channel width-to-length ratio (W/L) of the second transistor  524  is greater than a W/L of the first transistor  522 .  
         [0046]     Moreover, the method can further have more steps as follows. A third transistor  526  is switched on, and a second discharging path  530  through the scan line  502 , the third transistor  526 , the second transistor  524 , and the discharging line  510  is then provided. Thus, a second current is discharged via the second discharging path  530 . Furthermore, a fourth transistor  528  can be switched off.  
         [0047]     A first electrode of the third transistor  526  is electrically connected to the scan line  502 . A second electrode of the third transistor  526  is electrically connected to the second end of the resistance element  532 . A gate electrode of the third transistor  526  is electrically connected to the first end of the resistance element  532 . A first electrode of the fourth transistor  528  is electrically connected to the discharging line  510 . A second electrode of the fourth transistor  528  is electrically connected to the first end of the resistance element  532 . A gate electrode of the fourth transistor  528  is electrically connected to the discharging line  510 .  
         [0048]     In another aspect, the foregoing embodiments further disclose a display apparatus current leakage reducing method. A potential difference is provided between the scan line  502  and the discharging line  510 . When the first transistor  522  and the second transistor  524  are switched off, a leakage path through the scan line  502 , the resistance element  532 , and the discharging line  510  is provided. A leakage through the leakage path as stated above is reduced by the resistance element  532 .  
         [0049]     In the embodiment, the third transistor  526  and the fourth transistor  528  are both switched off while the first transistor  522  and the second transistor  524  are switched off. The material of the resistance element  532  is indium-tin oxide or amorphous silicon. For example, the resistance element  532  can be a thin film transistor or a diode.  
         [0050]     The first electrode of the third transistor  526  is electrically connected to the scan line  502 , the gate electrode of the third transistor  526  is electrically connected to the first end of the resistance element  532 , and the second electrode of the third transistor  526  is electrically connected to the second end of the resistance element  532 . The first electrode and the gate electrode of the fourth transistor  528  are electrically connected to the discharging line  510 , and the second electrode of the fourth transistor  528  is electrically connected to the first end of the resistance element  532 .  
         [0051]     It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.

Technology Category: 3