Patent Document

The present invention claims the benefit of Korean Application No. P2002-80711 filed in Korea on Dec. 17, 2002, which is hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a driving circuit of a liquid crystal display (LCD) device, and more particularly, to a bi-directional driving circuit of a LCD panel that enables a bi-directional driving regardless of the number of stages. 
     2. Discussion of the Related Art 
     In general, a LCD device commonly includes a driving circuit in an LCD panel, such as a gate driving integrated circuit (IC) and a data driving IC. Also, the LCD device has a fixed driving direction, so that system makers sometimes require various panels. 
       FIG. 1  is a circuit diagram of a liquid crystal display (LCD) panel according to the related art. In  FIG. 1 , a polysilicon thin film transistor liquid crystal display (TFT LCD) panel includes a pixel array, a plurality of first shift registers  11 , a plurality of first buffers  12 , a plurality of second shift registers  13 , and a plurality of second buffers  14 . In particular, the pixel array has a plurality of gate lines G 1 –G m  crossing a plurality of data lines D 1 –D n , such that the first shift registers  11  and buffers  12  supply scan signals GCLK and GSTART to each of the plurality of gate lines G 1 –G m , and the second shift registers  13  and buffers  14  supply other scan signals DCLK and DSTART to the plurality of data lines D 1 –D n . 
     In addition, the plurality of data lines D 1 –D n  are divided into a k-number of blocks, such that there are a k-number of second shift registers  13  and buffers  14 , and each of the k-number of second shift registers  13  and buffers  14  supplies scan signals through one of lines d 1 –d k  to each of the k-number of blocks of data lines D 1 –D n . Moreover, the LCD panel includes a signal bus  15  having a plurality of signal lines s 1 –s n  for transmitting video signals output from a digital-to-analog converter of a data driving circuit (not shown) to each of the plurality of data lines D 1 –D n , and a plurality of switching elements  16  for sequentially supplying video signals of the signal lines s 1 –s n  to each of the k-number of blocks of the data lines D 1 –D n  based on signals output from the second shift registers  13  and buffers  14 . 
     Thus, by dividing the data lines D 1 –D n  into blocks, the driving circuit has a reduced number of contact lines between an external circuit and the panel. However, in the block arrangement of the data lines D 1 –D n , the gate lines and the data lines are sequentially driven by the shift registers to display limited picture images. For example, since the shift registers shift in a fixed direction, the driving circuit then does not have freedom in a driving direction as required by some system makers, thereby requiring various panels. 
       FIG. 2  is a circuit diagram of a shift register of a LCD panel according to the related art. In  FIG. 2 , a start pulse VST, four clock signals CLK 1 –CLK 4  each having different phases, and power source voltages Vdd and Vss are input to a shift register. In addition, the shift register includes eight blocks of transistors each having similar structures, such that the power source voltages Vdd and Vss are similarly supplied to each of the eight blocks, but the four clock signals CLK 1 –CLK 4  are differently supplied to each of the eight blocks. 
     In particular, each of the eight blocks of transistors includes first, second, third, fourth, fifth, sixth, and seventh p-MOS transistors TFT 1 –TFT 7 . The first transistor TFT 1  has drain and gate terminals connected to either a VST terminal to which the start pulse VST is supplied to, or an output terminal of the previous block. Thus, in the first block, the drain and gate terminals of the first transistor TFT 1  are connected to the VST terminal, and in the second block, the drain and gate terminals of the first transistor TFT 1  are connected to a first output terminal Output 1  of the first block. 
     In addition, the second transistor TFT 2  has a drain terminal connected to a source terminal of the first transistor TFT 1 , and a gate terminal to which one of the four clock signals CLK 1 –CLK 4  is supplied. For example, in the first block, the fourth clock signal CLK 4  is supplied, and in the second block, the first clock signal CLK 1  is supplied. The third transistor TFT 3  has a source terminal connected to a source terminal of the second transistor TFT 2 , and a drain terminal connected to a Vss terminal to which the power source voltage Vss is supplied to. The fourth transistor TFT 4  has a drain terminal connected to a Vdd terminal to which the power source voltage Vdd is supplied to, a gate terminal to which another one of the four clock signals CLK 1 –CLK 4  is supplied, and a source terminal connected to a gate terminal of the third transistor TFT 3 . For example, in the first block, the third clock signal CLK 3  is supplied, and in the second block, the fourth clock signal CLK 4  is supplied. 
     Furthermore, the fifth transistor TFT 5  has a drain terminal connected to the gate terminal of the third transistor TFT 3  and the source terminal of the fourth transistor TFT 4 , and a source terminal connected to the Vss terminal. The fifth transistor TFT 5  also has a gate terminal connected to either the VST terminal or the output terminal of the previous block. Thus, in the first block, the gate terminal of the fifth transistor TFT 5  is connected to the VST terminal, and in the second block, the gate terminal of the fifth transistor TFT 5  is connected to the first output terminal, Output 1 . 
     Moreover, the sixth transistor TFT 6  has a drain terminal to which one of the four clock signals CLK 1 –CLK 4  is supplied, and a gate terminal connected to a node Q that is also connected to the source terminals of the second and third transistors TFT 2  and TFT 3 . For example, in the first block, the first clock signal CLK 1  is supplied, and in the second block, the second clock signal CLK 2  is supplied. The sixth transistor TFT 6  further has a source terminal connected to a corresponding output terminal. For example, in the first block, the source terminal of the sixth transistor TFT 6  is connected to the first output terminal Output 1 , and in the second block, the source terminal of the sixth transistor TFT 6  is connected to the second output terminal Output 2 . The seventh transistor TFT 7  has a drain terminal connected to the corresponding output terminal, a source terminal connected to the Vss terminal, and a gate terminal connected to another node QB that is also connected to the gate terminal of the third transistor TFT 3 , the drain terminal of the fifth terminal TFT 5 , and the source terminal of the fourth transistor TFT 4 . 
     Furthermore, a first capacitor C 1  connects and grounds the source terminal of the second transistor TFT 2  and the drain terminal of the third transistor TFT 3 . At the node Q, a second capacitor connects the gate terminal of the sixth transistor TFT 6  to the Vss terminal. A third capacitor connects the gate and the source terminals of the sixth, transistor TFT 6 . At node QB, a fourth capacitor connects the gate terminal of the seventh transistor TFT 7  and the Vss terminal. 
     In general, an output terminal of a previous block is connected to the drain and gate terminals of the first transistor TFT 1  of the next block and to the gate terminal of the fifth transistor TFT 5  of the next block. For example, the first output terminal Output 1  is connected to the drain and gate terminals of the first transistor TFT 1  of the second block and the gate terminal of the fifth transistor TFT 5  of the second block. In addition, the first clock signal CLK 1  is supplied to the drain terminal of the sixth transistor TFT 6  in each of the first and the fifth blocks, the gate terminal of the second transistor TFT 2  in each of the second and sixth blocks, and the gate terminal of the fourth transistor TFT 4  in each of the third and seventh blocks. The second clock signal CLK 2  is supplied to the drain terminal of the sixth transistor TFT 6  in each of the second block and the sixth blocks, the gate terminal of the second transistor TFT 2  in each of the third and seventh blocks, and the gate terminal of the fourth transistor TFT 4  in each of the fourth and eight blocks. 
     Moreover, the third clock signal CLK 3  is supplied to the gate terminal of the fourth transistor TFT 4  in each of the first and fifth blocks, the drain terminal of the sixth transistor TFT 6  in each of the third block and the seventh blocks, and the gate terminal of the second transistor TFT 2  in each of the fourth and eighth blocks. The fourth clock signal CLK 4  is supplied to the gate terminal of the second transistor TFT 2  of each of the first and fifth blocks, the gate terminal of the fourth transistor TFT 4  in each of the second and sixth blocks, and the drain terminal of the sixth transistor TFT 6  in each of the fourth block and the eighth blocks. 
       FIG. 3  illustrates input and output waveforms of the shift register of the LCD panel of  FIG. 2 . In  FIG. 3 , the clock signals CLK 1 –CLK 4  are sequentially LOW. For example, during a first time period, 0s–20 μs, the start pulse VST is LOW (0 V). Thus, in the first block, the first transistor TFT 1  is turned ON, and the fifth transistor TFT 5  is turned ON. Also, the fourth clock signal CLK 4  is LOW and the second transistor TFT 2  is also turned ON. Accordingly, the node Q becomes LOW, thereby turning the sixth transistor TFT 6  ON. As a result, the first clock signal CLK 1  is output to the first output terminal Output 1 . In addition, because the fifth transistor TFT 5  is turned ON, the node QB is HIGH (10V), thereby turning the seventh transistor TFT 7  OFF. Accordingly, the power source voltage Vss is not output to the first output terminal Output 1 . 
     During a second time period, 20μs–40 μs, the first clock signal CLK 1  is LOW, which is the output of the first block, and is supplied to the drain and gate terminals of the first transistor TFT 1  of the second block and the gate terminal of the fifth transistor TFT 5  of the second block. Thus, in the second block, the first, second, and fifth transistors TFT 1 , TFT 2 , and TFT 5  are turned ON, such that the node Q is HIGH, thereby turning the sixth transistor TFT 6  ON. Accordingly, the second clock signal CLK 2  is output to the second output terminal Output 2 . Similarly, because the fifth transistor TFT 5  is turned ON, the node QB is HIGH, thereby turning the seventh transistor TFT 7  OFF. Accordingly, the power source voltage Vss is not output to the second output terminal Output 2 . 
     However, the LCD panel according to the related art is disadvantageous. For example, picture images can be scanned only in an originally designed direction of the LCD panel, such that the LCD panel must generate images in the order of the first block to the last block. Accordingly, the LCD has only one fixed orientation, such that the LCD panel is not versatile and can not be flipped from a landscape orientation to a portrait type orientation. 
       FIG. 4  is a circuit diagram of a bi-directional shift register of an LCD panel according to the related art and U.S. patent application Ser. No. 10/082,125. In  FIG. 4 , a gate or data start pulse VST, four clock signals CLK 1 –CLK 4  each having different phases, and power source voltage Vdd and Vss may be input to a shift register. In addition, the shift register may include eight blocks of transistors each having similar structures, such that power source voltages Vdd and Vss may be similarly supplied to each of the eight blocks, but the four clock signals CLK 1 –CLK 4  may be differently supplied to each of the eight blocks. 
     In particular, each of the eight blocks may includes first, second, third, fourth, fifth, sixth, seventh, eighth, and ninth p-MOS transistor TFT 1 –TFT 9 . The first transistor may have drain and gate terminals connected to either a VST input terminal to which the start pulse VST is supplied, or an output terminal of the previous block. Thus, in the first block, the drain and gate terminals of the first transistor TFT 1  may be connected to the VST input terminal, and in the second block, the drain and gate terminals of the first transistor TFT 1  may be connected to a first output terminal Output 1 . 
     In addition, the second transistor TFT 2  may have a drain terminal connected to a source of the first transistor TFT 1 , and a gate terminal to which one of the four clock signals CLK 1 –CLK 4  is supplied. For example, in the first block, the fourth clock signal CLK 4  may be supplied, and in the second block, the first clock signal CLK 1  may be supplied. The third transistor TFT 3  may have a source terminal connected to a source of the second transistor TFT 2 , and a drain terminal connected to a Vss terminal to which the power source voltage Vss is supplied. The fourth transistor TFT 4  may have a drain terminal connected to a Vdd terminal to which the power source voltage Vdd supplied, and a gate terminal to which another one of the four clock signals CLK 1 –CLK 4  is supplied, and a source terminal connected to a gate terminal of the third p-MOS transistor TFT 3 . For example, in the first block, the third clock signal CLK 3  may be supplied, and in the second block, the fourth clock signal CLK 4  may be supplied. 
     Further, the fifth transistor TFT 5  may have a drain terminal connected at a node QB to the gate terminal of the third transistor TFT 3  and the source terminal of the fourth transistor TFT 4 , a gate terminal connected to a node Q, which is also connected to the source terminals of the second and third transistors TFT 2  and TFT 3 , and a source terminal connected to the Vss terminal. The sixth transistor TFT 6  may have a drain terminal to which one of the four clock signals CLK 1 –CLK 4  is supplied, a gate terminal connected to the node Q, and a source terminal connected to a corresponding output terminal. For example, in the first block, the first clock signal CLK 1  may be supplied, and in the second block, the second clock signal CLK 2  may be supplied. In addition, in the first block, the source terminal of the sixth transistor TFT 6  may be connected to the first output terminal Output 1 , and in the second block, the source terminal of the sixth transistor may be connected to the second output terminal Output 2 . 
     Moreover, the seventh transistor TFT 7  may have a drain terminal connected to the corresponding output terminal, a gate terminal connected to the node QB, and a source terminal connected to the Vss terminal. The eighth transistor TFT 8  may have drain and gate terminals connected to an output terminal of the next block, and a source terminal connected to the source terminal of the first transistor TFT 1 . For example, in the first block, the drain and gate terminals of the eight transistor may be connected to the second output terminal Output 2 . The ninth transistor TFT 9  may be connected in parallel to the second transistor TFT 2 , such that the drain terminal of the ninth transistor TFT 9  may be connected to the source terminal of the second transistor TFT 2 , and the source terminal of the ninth transistor TFT 9  may be connected to the drain terminal of the second transistor TFT 2 . In addition, the ninth transistor may have a gate terminal to which one of the four clock signals CLK 1 –CLK 4  is supplied. For example, in the first block, the second clock signal CLK 2  may be supplied, and in the second block, the third clock signal CLK 3  may be supplied. 
     Furthermore, a first capacitor may connect to and ground the source terminal of the first transistor TFT 1 , the drain terminal of the second transistor TFT 2 , and the source terminals of the eighth and ninth transistors TFT 8  and TFT 9 . A second capacitor may connect the gate terminal of the sixth p-MOS transistor TFT 6  to the Vss terminal. A third capacitor C 3  may connect to the gate and source terminals of TFT 6 . A fourth capacitor C 4  may connect the gate terminal of the seventh p-MOS transistor TFT 7  to the Vss terminal. Accordingly, the first clock signal CLK 1  may be supplied to the drain terminal of the sixth p-MOS transistor TFT 6  in the first and fifth blocks, the gate terminal of the second p-MOS transistor TFT 2  in the second and sixth blocks, the gate terminal of the fourth p-MOS transistor TFT 4  in the third and seventh blocks, and the gate terminal of the ninth p-MOS transistor TFT 9  in the fourth and eighth blocks. The second clock signal CLK 2  may be supplied to the gate terminal of the ninth p-MOS transistor TFT 9  in the first and fifth blocks, the drain terminal of the sixth p-MOS transistor TFT 6  in the second and sixth blocks, the gate terminal of the second p-MOS transistor TFT 2  in the third and seventh blocks, and the gate terminal of the fourth p-MOS transistor TFT 4  in the fourth and eighth blocks. 
     Also, the third clock signal CLK 3  may be supplied to the gate terminal of the fourth p-MOS transistor TFT 4  in the first and fifth blocks, the gate terminal of the ninth p-MOS transistor TFT 9  in the second and sixth blocks, the drain terminal of the sixth p-MOS transistor TFT 6  in the third and seventh blocks, and the gate terminal of the second p-MOS transistor TFT 2  in the fourth and eighth blocks. The fourth clock signal CLK 4  may be supplied to the gate terminal of the second p-MOS transistor TFT 2  in the first and fifth blocks, the gate terminal of the fourth p-MOS transistor TFT 4  in the second and sixth blocks, the gate terminal of the ninth p-MOS transistor TFT 9  in the third and seventh blocks, and the drain terminal of the sixth p-MOS transistor TFT 6  in the fourth and eighth blocks. 
       FIG. 5  illustrates forward input and output waveforms of the shift register of the LCD panel of  FIG. 4 . In  FIG. 5 , the clock signals CLK 1 –CLK 4  may be sequentially set LOW. For example, during a first time period, 0 s–20 μs, the start pulse VST may be set LOW (0V). Thus, in the first block in  FIG. 4 , the first and fifth transistors TFT 1  and TFT 5  may be turned ON. Also, the fourth clock signal CLK 4  may be set LOW, thereby turning the second transistor TFT 2  ON. Accordingly, the node Q may become LOW, thereby turning the sixth transistor TFT 6  ON. As a result, the first clock signal CLK 1  may be outputted to the first output terminal Output 1 . In addition, because the fifth transistor TFT 5  may be turned ON, the node QB may be set HIGH (10V), thereby turning the seventh transistor OFF. Accordingly, the power source voltage Vss may not be outputted to the first output terminal Output 1 . 
     In addition, during a second time period, 20 μs–40 μs, the first clock signal CLK 1  may be set LOW, which is the output of the first block, and may be supplied to the drain and gate terminals of the first transistor TFT 1  of the second block. Thus, in the second block, the first and second transistors TFT 1  and TFT 2  may be turned ON, thereby turning the sixth transistor TFT 6  ON. As a result, the second clock signal CLK 2  may be outputted to the second output terminal Output 2 . 
       FIG. 6  illustrates backward input and output waveforms of the shift register of the LCD panel of  FIG. 4 . In  FIG. 6 , the clock signals CLK 1 –CLK 4  may be set LOW in reverse sequence. For example, during a first period, 0 s–20 μs, the start pulse VST may be set LOW. Thus, in the first block, the first transistor TFT 1  may be turned ON. Also, the fourth clock signal CLK 4  may be set HIGH, thereby turning the second transistor TFT 2  OFF. As a result, the sixth transistor TFT 6  may be turned OFF, thereby failing to output the first clock signal CLK 1  to the first output terminal Output 1 . 
     However, in the eighth block, the first transistor TFT 1  and the ninth transistor TFT 9  may be both turned ON. As a result, the sixth transistor TFT 6  of the eighth block may be turned ON, thereby outputting the fourth clock signal CLK 4  to the eight output terminal Output 8 . 
     In addition, the output signal from the eighth output terminal Output 8  may be supplied to the eighth transistor TFT 8  of the seventh block. Then, the fourth clock signal CLK 4  may be set LOW, thereby turning the eighth and ninth transistors TFT 8  and TFT 9  in the seventh block ON. As a result, the sixth transistor TFT 6  of the seventh block may be turned ON, thereby outputting the third clock signal CLK 3  to the seventh output terminal Output 7 . 
     Accordingly, the start pulse VST may be synchronized with the first clock signal CLK 1  to output the fourth to first clock signals CLK 4 –CLK 1  in sequence, starting from the eighth block to the first block. Thus, the shift register of  FIG. 4  may provide both forward and backward scanning in a LCD panel, such that the LCD panel may function in both landscape and portrait orientations. However, such LCD panel may experience image distortions when it has a number of blocks of transistors that is not a multiple of 4. 
       FIG. 7  is a circuit diagram of a shift register of an LCD panel having five stages of  FIG. 4 . In  FIG. 7 , a shift register may have first, second, third, fourth and fifth blocks of p-MOS transistors similar to the first-fourth blocks of transistors in  FIG. 4 , except the gate and drain terminals of the eighth transistor in the fifth block may be connected to the VST terminal. 
       FIG. 8  illustrates forward input and output waveforms of the shift register of the LCD panel of  FIG. 7 . In  FIG. 8 , the four clock signals CLK 1 –CLK 4  may be set LOW in sequence. For example, during a first time period, 0 s–20 μs when the start pulse VST may be LOW, in the first block, the first transistor TFT 1  may be ON). Also, the fourth clock signal CLK 4  may be LOW, the second transistor TFT 2  may be ON. As a result, the node Q may become LOW, thereby turning the sixth transistor TFT 6  ON. Accordingly, the first clock signal CLK 1  may be outputted to the first output terminal Output 1 . In addition, the node QB may become HIGH, thereby turning the seventh transistor TFT 7  OFF. Accordingly, the Vss voltage may not be outputted to the first output terminal Output 1 . 
     In addition, during the first time period, the LOW-level start pulse VST may also be inputted to the gate terminal of the eighth transistor TFT 8  in the fifth block. Since the fourth clock signal CLK 4  may also be LOW, the second transistor TFT 2  may be turned ON. As a result, the node Q may be LOW, thereby turning the sixth transistor TFT 6  ON. Hence, the first clock signal CLK 1  may also be outputted to the fifth output terminal Output 5 . Accordingly, two outputs may be erroneously generated both at the first and fifth output terminals Output 1  and Output 5  during about 20–40 μs. 
       FIG. 9  illustrates backward input and output waveforms of the shift register of the LCD panel of  FIG. 7 . In  FIG. 9 , two outputs may also erroneously generated both at the first and fifth output terminals Output 1  and Output 5  during about 20–40 μs. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention is directed to a bi-directional driving circuit of a liquid crystal display (LCD) panel that substantially obviates one or more problems due to limitations and disadvantages of the related art. 
     An object of the present invention is to provide to a bi-directional driving circuit of a liquid crystal display (LCD) panel, which can scan in forward and backward directions without an additional input pad, and enables a bi-directional driving regardless of the number of stages. 
     Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings. 
     To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described herein, the driving device of a liquid crystal display (LCD) panel includes a plurality of blocks arranged in sequence, each of the blocks comprising: a first switching element having drain and gate terminals to which one of a start pulse and an output signal of a previous block in the sequence is supplied, a second switching element having a drain terminal connected to a source terminal of the first switching element, and a gate terminal to which a first clock signal is supplied, a third switching element having a source terminal connected to a source terminal of the second switching element, and a drain terminal connected to a first voltage input terminal, a fourth switching element having a drain terminal connected to a second voltage input terminal, a gate terminal to receive a second clock signal that is not supplied to the second switching element, and a source terminal connected to a gate terminal of the third switching element, a fifth-switching element having a drain terminal connected to the source terminal of the fourth switching element, a gate terminal connected to a contact node between the source terminals of the second and third switching elements, and a source terminal connected to the first voltage input terminal, a sixth switching element having a drain terminal to receive a third clock signal that is not supplied to the second and fourth switching elements, a gate terminal connected to the contact node, and a source terminal connected to a corresponding output terminal, a seventh switching element having a drain terminal connected to the corresponding output terminal, a gate terminal connected to the source terminal of the fourth switching element and the gate terminal of the third switching element, and a source terminal connected to the first voltage input terminal, an eighth switching element having drain and gate terminals to which one of the start pulse is supplied and connected to an output terminal of the next block in the sequence, and a ninth switching element having a source terminal connected to the source terminal of the eighth switching element, a gate terminal to receive a fourth clock signal that is not supplied to the second, fourth, and sixth switching elements, and a drain terminal connected to the source terminal of the second switching element and the gate terminal of the sixth switching element. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention. In the drawings: 
         FIG. 1  is a circuit diagram of a liquid crystal display (LCD) panel according to the related art; 
         FIG. 2  is a circuit diagram of a shift register of a LCD panel according to the related art; 
         FIG. 3  illustrates input and output waveforms of the shift register of the LCD panel of  FIG. 2 ; 
         FIG. 4  is a circuit diagram of a bi-directional shift register of an LCD panel according to the related art; 
         FIG. 5  illustrates forward input and output waveforms of the shift register of the LCD panel of  FIG. 4  according to the related art; 
         FIG. 6  illustrates backward input and output waveforms of the shift register of the LCD panel of  FIG. 4  according to the related art; 
         FIG. 7  is a circuit diagram of a shift register of an LCD panel having five stages of  FIG. 4  according to the related art; 
         FIG. 8  illustrates forward input and output waveforms of the shift register of the LCD panel of  FIG. 7  according to the related art; 
         FIG. 9  illustrates backward input and output waveforms of the shift register of the LCD panel of  FIG. 7  according to the related art; 
         FIG. 10  is a circuit diagram of an exemplary shift register of an LCD panel according to the present invention; 
         FIG. 11  illustrates forward input and output waveforms of the exemplary shift register of the LCD panel of  FIG. 10  according to the present invention; and 
         FIG. 12  illustrates backward input and output waveforms of the exemplary shift register of the LCD panel of  FIG. 10  according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. 
       FIG. 10  is a circuit diagram of an exemplary shift register of an LCD panel according to the present invention. In  FIG. 10 , a gate or data start pulse VST, four clock signals CLK 1 –CLK 4  each having different phases, and power drain voltages Vdd and Vss may be input to a shift register. In addition, the shift register may have five blocks of transistor each having similar structures. Each of the five blocks may include first, second, third, fourth, fifth, sixth, seventh, eight, and ninth p-MOS transistor TFT 1 –TFT 9 . In particular, the first transistor TFT 1  may have drain and gate terminals to which the start pulse VST is supplied or connected to an output terminal of the previous block. For example, in the, first block, the drain and gate terminals of the first transistor TFT 1  may be connected to receive the start pulse VST, and in the second block, the drain and gate terminals of the first transistor TFT 1  may be connected to the first output terminal Output 1 . The second transistor TFT 2  may have a drain terminal connected to a source terminal of the first transistor TFT 1 , and a gate terminal to which one of the four clock signals CLK 1 –CLK 4  may be supplied. For example, in the first block, the fourth clock signal CLK 4  may be supplied, and in the second block, the first clock signal CLK 1  may be supplied. 
     In addition, the third transistor TFT 3  may have a source terminal connected to a source terminal of the second transistor TFT 2 , and a drain terminal connected to the Vss terminal. The fourth transistor TFT 4  may have a drain terminal connected to the Vdd terminal, a gate terminal to which one of the four clock signals CLK 1 –CLK 4  is supplied, and a source terminal connected at a node QB to a gate terminal of the third transistor TFT 3 . For example, in the first block, the third clock signal CLK 3  may be supplied, and in the second block, the fourth clock signal CLK 4  may be supplied. The fifth transistor TFT 5  may have a drain terminal connected at the node QB to the source terminal of the fourth transistor TFT 4 , a gate terminal connected to a contact node Q between the source terminal of the second transistor TFT 2  and the source terminal of the third transistor TFT 3 , and a source terminal connected to the Vss terminal. 
     Further, the sixth transistor TFT 6  may have a drain terminal to which one of the four clock signals CLK 1 –CLK 4  is supplied, a gate terminal connected at the node Q to the source terminal of the second transistor TFT 2 , and a source terminal connected to a corresponding output terminal. For example, in the first block, the first clock signal CLK 1  may be supplied, and in the second block, the second clock signal CLK 2  may be supplied. In addition, in the first block, the source terminal of the sixth transistor TFT 6  may be connected to the first output terminal Output 1 , and in the second block, the source terminal of the sixth transistor TFT 6  may be connected to the second output terminal Output 2 . The seventh transistor TFT 7  may have a drain terminal connected to the corresponding output terminal as the source terminal of the sixth transistor TFT 6 , a gate terminal connected at the node QB to the source terminal of the fourth transistor TFT 4  and the gate terminal of the third transistor TFT 3 , and a source terminal connected to the Vss terminal. 
     The eighth transistor TFT 8  may have drain and gate terminals connected to an output terminal of the next block. For example, in the first block, the drain and gate terminal of the eighth transistor TFT 8  may be connected to the second output terminal Output 2 . Moreover, in the fifth block, the drain and gate terminals of the eight transistor TFT 8  may instead receive the start pulse VST. The ninth transistor TFT 9  may have a source terminal connected to a source terminal of the eighth transistor TFT 8 , a gate terminal to which one of the four clock signals CLK 1 –CLK 4  is supplied, and a drain terminal connected at the node Q to the source terminal of the second transistor TFT 2  and the gate terminal of the sixth transistor TFT 6 . For example, in the first block, the second clock signal CLK 2  may be supplied, and in the second block, the third clock signal CLK 3  may be supplied. 
     Moreover, a first capacitor may connect the gate terminal of the sixth transistor TFT 6  to the Vss terminal. A second capacitor C 2  may connect between the gate and source terminals of the sixth transistor TFT 6 . In addition, a third capacitor C 3  may connect the gate terminal of the seventh transistor TFT 7  to the Vss terminal. 
     Accordingly, the first clock signal CLK 1  may be supplied to the drain terminal of the sixth transistor TFT 6  in the first and the fifth blocks, the gate terminal of the second transistor TFT 2  in the second block, the gate terminal of the fourth transistor TFT 4  in the third block, and the gate terminal of the ninth transistor TFT 9  in the fourth block. The second clock signal CLK 2  may be supplied to the gate terminal of the ninth transistor TFT 9  in the first and fifth blocks, the drain terminal of the sixth transistor TFT 6  in the second block, the gate terminal of the second transistor TFT 2  in the third block, and the gate terminal of the fourth transistor TFT 4  in the fourth block. 
     In addition, the third clock signal CLK 3  may be supplied to the gate terminal of the fourth transistor TFT 4  in the first and fifth blocks, the gate terminal of the ninth transistor TFT 9  in the second block, the drain terminal of the sixth transistor TFT 6  in the third block, and the gate terminal of the second transistor TFT 2  in the fourth block. The fourth clock signal CLK 4  may be supplied to the gate terminal of the second transistor TFT 2  in the first and fifth blocks, the gate terminal of the fourth transistor TFT 4  in the second block, the gate terminal of the ninth transistor TFT 9  in the third block, the drain terminal of the sixth transistor TFT 6  in the fourth block. Although not shown, if the driving circuit includes eight blocks, the clock signal may be equally supplied to each block of transistors. 
       FIG. 11  illustrates forward input and output waveforms of the exemplary shift register of the LCD panel of  FIG. 10  according to the present invention. In  FIG. 11 , the four clock signals may be LOW in sequence. For example, during a first time period, about 0 s–20 μs, the start pulse may be set LOW (0V), thereby turning the first transistor TFT 1  (of the first block in  FIG. 10 ) ON. Also, the fourth clock signal CLK 4  may be LOW, thereby turning the second transistor TFT 2  (in  FIG. 10 ) ON. As a result, the node Q (in  FIG. 10 ) may become LOW. Accordingly, the sixth transistor TFT 6  (in  FIG. 10 ) may be turned ON, thereby supplying the first clock signal CLK 1  to the first output terminal Output 1  (in  FIG. 10 ). In addition, since the second transistor TFT 2  (in  FIG. 10 ) may be ON, the fifth transistor TFT 5  (in  FIG. 10 ) may also be turned ON, thereby setting the node QB HIGH (10V) as the Vss voltage. Thus, the seventh transistor TFT 7  (in  FIG. 10 ) may be turned OFF, and the Vss voltage may not be supplied to the first output terminal Output 1  (in  FIG. 10 ). 
     During a second time period, about 20 μs–40 μs, the first clock signal may be LOW, which may be supplied through the first output terminal Output  1  (in  FIG. 10 ) to the gate terminal of the first transistor TFT 1  (of the second block in  FIG. 10 ), and may be directly supplied to the gate terminal of the second transistor TFT 2  (in the second clock in  FIG. 10 ). Thus, the first and second transistors TFT 1  and TFT 2  (in  FIG. 10 ) may be ON, thereby turning the sixth transistor TFT 6  (in  FIG. 10 ) ON. Accordingly, the second clock signal CLK 2  may be supplied to the second output terminal Output 2  (in  FIG. 10 ). 
     Turning to the fifth block (in  FIG. 10 ), during the first time period when the start pulse VST is set LOW, the second clock signal CLK 2  may be set HIGH, thereby turning the ninth transistor TFT 9  OFF, even though the eighth transistor TFT 8  may be turned ON. Since the ninth transistor TFT 9  may be turned OFF, the node Q may be HIGH. Thus, the sixth transistor TFT 6  may be OFF and may not output the first clock signal CLK 1  to the fifth output terminal Output 5 . Accordingly, in the fifth block, an output may be generated only when an output of a previous block is supplied in a switch-ON state to the first transistor TFT 1 , and not when the start pulse VST is set LOW. 
     Accordingly, the start pulse VST may be initially synchronized with the fourth clock signal CLK 4 , and the first to third clock signals CLK 1  to CLK 3  may be sequentially generated, thereby sequentially supplying the four clock signals in a sequence. 
       FIG. 12  illustrates backward input and output waveforms of the exemplary shift register of the LCD panel of  FIG. 10  according to the present invention. In  FIG. 12 , the four clock signals may be set LOW in a reverse sequence. For example, in a first time period, about 0 s–20 μs, the start pulse VST and the second clock signal may be set LOW. Thus, in the first block (in  FIG. 10 ), the first transistor TFT 1  may be turned ON, the second transistor TFT 2  may be turned OFF, thereby turning the sixth transistor TFT 6  OFF. As a result, the first block may not supply the first clock signal CLK 1  to the first output terminal Output 1  (in  FIG. 10 ). However, in the fifth block (in  FIG. 10 ), the eighth transistor TFT 8  and the ninth transistor TFT 9  may be turned ON, thereby turning the sixth transistor TFT 6  ON. As a result, the first clock signal CLK 1  may be supplied to the fifth input terminal Output 5  (in  FIG. 10 ). 
     In addition, during a second time period, about 20 μs–40 μs, the signal supplied from the fifth output terminal Output 5  may then be supplied to the eighth transistor TFT 8  in the fourth block (in  FIG. 10 ). Also, the first clock signal CLK 1  may become LOW, thereby turning the eighth and ninth transistors TFT 8  and TFT 9  in the fourth block (in  FIG. 10 ) ON. As a result, the sixth transistor TFT 6  (in  FIG. 10 ) may also be turned ON, thereby supplying the fourth clock signal CLK 4  to the fourth output terminal Output 4  (in  FIG. 10 ). Hence, the start pulse VST may be initially synchronized with the second clock signal CLK 2 , and the first to fourth and third clock signals CLK 1  to CLK 4  and CLK 3  may be sequentially generated, thereby repeatedly supplying the four clock signals in a reverse sequence. 
     Accordingly, the shift register may be driven bi-directionally, such that an LCD panel may operate regardless of panel orientation. In addition, the shift register may be driven without error regardless of how many blocks of transistors it may have. 
     It will be apparent to those skilled in the art that various modifications and variations can be made in the bi-direction driving circuit and the bi-direction driving method of a liquid crystal display pane of the present invention. Thus, it is intended that the present invention covers the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.

Technology Category: g