Abstract:
A shift register circuit includes plural shift register stages for providing plural gate signals. The Nth shift register stage of the shift register stages includes an input unit, a pull-up unit and a pull-down unit. The input unit is put in use for outputting an Nth driving control voltage according to an (N−1)th gate signal and an (N−2)th driving control voltage which are generated respectively by the (N−1) th shift register stage and the (N−2) th shift register stage of the shift register stages. The pull-up unit pulls up an Nth gate signal according to the Nth driving control voltage and a system clock. The pull-down unit pulls down the Nth gate signal and the Nth driving control voltage according to an (N+2)th gate signal generated by the (N+2)th shift register stage of the shift register stages.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a shift register circuit, and more particularly, to a shift register circuit having high driving ability. 
         [0003]    2. Description of the Prior Art 
         [0004]    Liquid crystal displays (LCDs) have advantages of a thin profile, low power consumption, and low radiation, and are broadly adopted for application in media players, mobile phones, personal digital assistants (PDAs), computer displays, and flat screen televisions. The operation of a liquid crystal display is featured by modulating the voltage drop across opposite sides of a liquid crystal layer for twisting the angles of liquid crystal molecules in the liquid crystal layer so that the transmittance of the liquid crystal layer can be controlled for illustrating images with the aid of light source provided by a backlight module. In general, the liquid crystal display comprises plural pixel units, a source driver, and a shift register circuit. The source driver is utilized for providing plural data signals to be written into the pixel units. The shift register circuit comprises a plurality of shift register stages and functions to generate plural gate signals for controlling the operations of writing the data signals into the pixel units. That is, the shift register circuit is a crucial device for providing a control of writing the data signals into the pixel units. 
         [0005]      FIG. 1  is a schematic diagram showing a prior-art shift register circuit. As shown in  FIG. 1 , the shift register circuit  100  comprises a plurality of shift register stages and, for ease of explanation, illustrates an (N−1) th shift register stage  111 , an Nth shift register stage  112  and an (N+1) th shift register stage  113 . Each shift register stage is employed to generate one corresponding gate signal furnished to one corresponding gate line according to a gate signal generated by one preceding shift register stage. For instance, the (N−1) th shift register stage  111  is utilized for generating a gate signal SGn−1 furnished to a gate line GLn−1 according to a gate signal SGn−2, the Nth shift register stage  112  is utilized for generating a gate signal SGn furnished to a gate line GLn according to the gate signal SGn−1, and the (N+1)th shift register stage  113  is utilized for generating a gate signal SGn+1 furnished to a gate line GLn+1 according to the gate signal SGn. In the operation of the Nth shift register stage  112 , the input transistor  181  of an input unit  180  comprises a first end for receiving the gate signal SGn−1, a gate end for receiving a control signal, and a second end for outputting a driving control voltage VQn. As the gate signal SGn−1 and the control signal are both at a high-level voltage, the second end of the input transistor  181  outputs the driving control voltage VQn which is lower than the high-level voltage by the threshold voltage of the input transistor  181 . Thereafter, the driving control voltage VQn is further pulled up to an active voltage by the rising edge of a system clock CK through coupling of the device capacitor of a pull-up transistor  191  in a pull-up unit  190 . The active voltage is then employed to drive the pull-up unit  190  for generating the gate signal SGn. However, the active voltage is lower than twice the high-level voltage by the threshold voltage of the input transistor  181 . That is, the output driving ability of the pull-up unit  190  is significantly lowered by the threshold voltage of the input transistor  181  in the operation of the Nth shift register stage  112 . 
       SUMMARY OF THE INVENTION 
       [0006]    In accordance with one embodiment of the present invention, a shift register circuit is disclosed for providing plural gate signals to plural gate lines. The shift register circuit comprises a plurality of shift register stages. And an Nth shift register stage of the shift register stages comprises an input unit, a pull-up unit, an energy-store unit, and a pull-down unit. 
         [0007]    The input unit is electrically connected to an (N−1)th shift register stage of the shift register stages for receiving an (N−1)th gate signal of the gate signals, and is electrically connected to an (N−2)th shift register stage of the shift register stages for receiving an (N−2)th driving control voltage. The input unit is utilized for outputting an Nth driving control voltage according to the (N−1)th gate signal and the (N−2)th driving control voltage. The pull-up unit, electrically connected to the input unit and an Nth gate line of the gate lines, is utilized for pulling up an Nth gate signal of the gate signals according to the Nth driving control voltage and a system clock. The Nth gate line is employed to transmit the Nth gate signal. The energy-store unit, electrically connected to the pull-up unit and the input unit, is employed to perform a charging/discharging process based on the Nth driving control voltage. The pull-down unit is electrically connected to the input unit and the Nth gate line, and is electrically connected to an (N+2)th shift register stage of the shift register stages for receiving an (N+2)th gate signal of the gate signals. The pull-down unit is utilized for pulling down the Nth gate signal and the Nth driving control voltage according to the (N+2)th gate signal. 
         [0008]    In accordance with another embodiment of the present invention, a shift register circuit is disclosed for providing plural gate signals to plural gate lines. The shift register circuit comprises a plurality of shift register stages. And an Nth shift register stage of the shift register stages comprises an input unit, a pull-up unit, a carry unit, an energy-store unit, and a pull-down unit. 
         [0009]    The input unit is electrically connected to an (N−1)th shift register stage of the shift register stages for receiving an (N−1)th start pulse signal, and is electrically connected to an (N−2) th shift register stage of the shift register stages for receiving an (N−2)th driving control voltage. The input unit is utilized for outputting an Nth driving control voltage according to the (N−1)th start pulse signal and the (N−2)th driving control voltage. The pull-up unit, electrically connected to the input unit and an Nth gate line of the gate lines, is utilized for pulling up an Nth gate signal of the gate signals according to the Nth driving control voltage and a system clock. The Nth gate line is employed to transmit the Nth gate signal. The carry unit, electrically connected to the input unit, is utilized for outputting an Nth start pulse signal according to the Nth driving control voltage and the system clock. The energy-store unit, electrically connected to the pull-up unit and the input unit, is employed to perform a charging/discharging process based on the Nth driving control voltage. The pull-down unit is electrically connected to the input unit and the Nth gate line, and is electrically connected to an (N+2)th shift register stage of the shift register stages for receiving an (N+2)th gate signal of the gate signals. The pull-down unit is utilized for pulling down the Nth gate signal and the Nth driving control voltage according to the (N+2)th gate signal. 
         [0010]    These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  is a schematic diagram showing a prior-art shift register circuit. 
           [0012]      FIG. 2  is a schematic diagram showing a shift register circuit in accordance with a first embodiment of the present invention. 
           [0013]      FIG. 3  is a schematic diagram showing related signal waveforms regarding the operation of the shift register circuit illustrated in  FIG. 2 , having time along the abscissa. 
           [0014]      FIG. 4  is a schematic diagram showing another embodiment of the Nth shift register stage of the shift register circuit illustrated in  FIG. 2 . 
           [0015]      FIG. 5  is a schematic diagram showing a shift register circuit in accordance with a second embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. Here, it is to be noted that the present invention is not limited thereto. 
         [0017]      FIG. 2  is a schematic diagram showing a shift register circuit in accordance with a first embodiment of the present invention. As shown in  FIG. 2 , the shift register circuit  200  comprises a plurality of shift register stages and, for ease of explanation, illustrates an (N−2)th shift register stage  211 , an (N−1)th shift register stage  212 , an Nth shift register stage  213 , an (N+1)th shift register stage  214  and an (N+2)th shift register stage  215 . For the sake of brevity, only the internal structure of the Nth shift register stage  213  is exemplified in detail. The internal structures of other shift register stages are similar to the Nth shift register stage  213  and can be inferred by analogy. In the operation of the shift register circuit  200 , the Nth shift register stage  213  is utilized for performing a circuit operation with high driving ability to generate a gate signal SGn and a driving control voltage VQn according to a driving control voltage VQn−2 generated by the (N−2)th shift register stage  211 , a gate signal SGn−1 generated by the (N−1)th shift register stage  212 , a gate signal SGn+2 generated by the (N+2)th shift register stage  215 , a first system clock HC 1 , a first clock LC 1 , a second clock LC 2  having a phase opposite to the first clock LC 1 , and a power voltage Vss. The circuit functions of other shift register stages are similar to the Nth shift register stage  213  and can be inferred by analogy. Regarding the system clocks HC 1 -HC 4  shown in  FIG. 2 , it is noted that the third system clock HC 3  has a phase opposite to the first system clock HC 1 , the second system clock HC 2  has a 90-degree phase difference relative to the first system clock HC 1 , and the fourth system clock HC 4  has a phase opposite to the second system clock HC 2 . 
         [0018]    The Nth shift register stage  213  comprises an input unit  305 , a pull-up unit  310 , an energy-store unit  315 , a pull-down unit  325 , a first auxiliary pull-down unit  330 , a first control unit  340 , a second auxiliary pull-down unit  350 , and a second control unit  360 . The input unit  305  is electrically connected to the (N−1)th shift register stage  212  for receiving the gate signal SGn−1, and is further electrically connected to the (N−2)th shift register stage  211  for receiving the driving control voltage VQn−2. The input unit  305  is utilized for outputting the driving control voltage VQn according to the gate signal SGn−1 and the driving control voltage VQn−2. The pull-up unit  310 , electrically connected to the input unit  305  and the gate line GLn, is utilized for pulling up the gate signal SGn of the gate line GLn according to the driving control voltage VQn and the first system clock HC 1 . The gate line GLn is employed to transmit the gate signal SGn. The energy-store unit  315 , electrically connected to the input unit  305  and the pull-up unit  310 , functions to perform a charging/discharging process based on the driving control voltage VQn. The pull-down unit  325  is electrically connected to the input unit  305  and the gate line GLn, and is further electrically connected to the (N+2) th shift register stage  215  for receiving the gate signal SGn+2. The pull-down unit  325  is utilized for pulling down the gate signal SGn and the driving control voltage VQn according to the gate signal SGn+2. 
         [0019]    The first control unit  340 , electrically connected to the input unit  305 , is utilized for generating a first control signal SCn 1  according to the driving control voltage VQn and the first clock LC 1 . The first auxiliary pull-down unit  330 , electrically connected to the first control unit  340 , the input unit  305  and the gate line GLn, is utilized for pulling down the gate signal SGn and the driving control voltage VQn according to the first control signal SCn 1 . The second control unit  360 , electrically connected to the input unit  305 , is utilized for generating a second control signal SCn 2  according to the driving control voltage VQn and the second clock LC 2 . The second auxiliary pull-down unit  350 , electrically connected to the second control unit  360 , the input unit  305  and the gate line GLn, is utilized for pulling down the gate signal SGn and the driving control voltage VQn according to the second control signal SCn 2 . 
         [0020]    In the embodiment shown in  FIG. 2 , the input unit  305  comprises a first transistor  306 , the pull-up unit  310  comprises a second transistor  311 , the energy-store unit  315  comprises a capacitor  316 , the pull-down unit  325  comprises a third transistor  326  and a fourth transistor  327 , the first auxiliary pull-down unit  330  comprises a ninth transistor  331  and a tenth transistor  332 , and the second auxiliary pull-down unit  350  comprises a fifteenth transistor  351  and a sixteenth transistor  352 . It is noted that each of the transistors aforementioned or to be mentioned may be a thin film transistor (TFT), a field effect transistor (FET) or other similar device having connection/disconnection switching functionality. 
         [0021]    The first transistor  306  comprises a first end electrically connected to the (N−1)th shift register stage  212  for receiving the gate signal SGn−1, a gate end electrically connected to the (N−2)th shift register stage  211  for receiving the driving control voltage VQn−2, and a second end for outputting the driving control voltage VQn. The second transistor  311  comprises a first end for receiving the first system clock HC 1 , a gate end electrically connected to the second end of the first transistor  306  for receiving the driving control voltage VQn, and a second end electrically connected to the gate line GLn. The capacitor  316  is electrically connected between the gate and second ends of the second transistor  311 . The third transistor  326  comprises a first end electrically connected to the gate line GLn, a gate end electrically connected to the (N+2) th shift register stage  215  for receiving the gate signal SGn+2, and a second end for receiving the power voltage Vss. The fourth transistor  327  comprises a first end electrically connected to the second end of the first transistor  306 , a gate end electrically connected to the (N+2)th shift register stage  215  for receiving the gate signal SGn+2, and a second end for receiving the power voltage Vss. 
         [0022]    The ninth transistor  331  comprises a first end electrically connected to the gate line GLn, a gate end electrically connected to the first control unit  340  for receiving the first control signal SCn 1 , and a second end for receiving the power voltage Vss. The tenth transistor  332  comprises a first end electrically connected to the second end of the first transistor  306 , a gate end electrically connected to the first control unit  340  for receiving the first control signal SCn 1 , and a second end electrically connected to the gate line GLn. The fifteenth transistor  351  comprises a first end electrically connected to the gate line GLn, a gate end electrically connected to the second control unit  360  for receiving the second control signal SCn 2 , and a second end for receiving the power voltage Vss. The sixteenth transistor  352  comprises a first end electrically connected to the second end of the first transistor  306 , a gate end electrically connected to the second control unit  360  for receiving the second control signal SCn 2 , and a second end electrically connected to the gate line GLn. 
         [0023]      FIG. 3  is a schematic diagram showing related signal waveforms regarding the operation of the shift register circuit  200  illustrated in  FIG. 2 , having time along the abscissa. The signal waveforms in  FIG. 3 , from top to bottom, are the second system clock HC 2 , the third system clock HC 3 , the fourth system clock HC 4 , the first system clock HC 1 , the driving control voltage VQn- 2 , the gate signal SGn−1, the driving control voltage VQn, the gate signal SGn, and the gate signal SGn+2. As shown in  FIG. 3 , during an interval T 1 , the (N−2) th shift register stage  211  employs the driving control voltage VQn−4 and the gate signal SGn−3 to pull the driving control voltage VQn−2 up to the high-level voltage VGH of system clock. During an interval T 2 , the (N−2) th shift register stage  211  employs the rising edge of the third system clock HC 3  to pull the driving control voltage VQn−2 further up to approximate 2VGH. During an interval T 3 , the (N−1) th shift register stage  212  outputs the gate signal SGn−1 having the high-level voltage VGH while the driving control voltage VQn−2 retains the voltage of approximate 2VGH. For that reason, the first transistor  306  of the Nth shift register stage  213  is capable of pulling the driving control voltage VQn up to the high-level voltage VGH according to the driving control voltage VQn−2 and the gate signal SGn−1 during the interval T 3 . It is noted that since the voltage at the gate end of the first transistor  306  approximates 2VGH during the interval T 3 , the driving control voltage VQn at the second end of the first transistor  306  is able to reach the high-level voltage VGH, i.e. without being lowered by the threshold voltage of the first transistor  306 . During an interval T 4 , the driving control voltage VQn is further boosted from VGH to approximate 2VGH by the rising edge of the first system clock HC 1  through coupling of the device capacitor of the second transistor  311 , and the second transistor  311  is then turned on for pulling the gate signal SGn up to the high-level voltage VGH. 
         [0024]    During an interval T 5 , the (N+2)th shift register stage  215  outputs the gate signal SGn+2 having the high-level voltage VGH, and therefore the third transistor  326  and the fourth transistor  327  of the Nth shift register stage  213  are both turned on by the gate signal SGn+2 for pulling the gate signal SGn and the driving control voltage VQn down to the power voltage Vss. According to the above description regarding the operation of the Nth shift register stage  213 , the gate signal SGn is pulled up by the second transistor  311  having high output driving ability according to the driving control voltage VQn of approximate 2VGH, thereby enhancing pixel charging rate to improve display quality. 
         [0025]      FIG. 4  is a schematic diagram showing another embodiment of the Nth shift register stage of the shift register circuit illustrated in  FIG. 2 . As shown in  FIG. 4 , the Nth shift register stage  413  is similar to the Nth shift register stage  213  shown in  FIG. 2 , differing in that the first control unit  340  is replaced with a first control unit  440 , and the second control unit  360  is replaced with a second control unit  460 . In the embodiment shown in  FIG. 4 , the first control unit  440  comprises a fifth transistor  341 , a sixth transistor  342 , a seventh transistor  343  and an eighth transistor  344 , and the second control unit  460  comprises an eleventh transistor  361 , a twelfth transistor  362 , a thirteenth transistor  363  and a fourteenth transistor  364 . 
         [0026]    The fifth transistor  341  comprises a first end for receiving the first clock LC 1 , a second end for outputting the first control signal SCn 1 , and a gate end electrically connected to the seventh transistor  343 . The sixth transistor  342  comprises a first end electrically connected to the second end of the fifth transistor  341 , a gate end electrically connected to the second end of the first transistor  306 , and a second end for receiving the power voltage Vss. The seventh transistor  343  comprises a first end for receiving the first clock LC 1 , a gate end for receiving the first clock LC 1 , and a second end electrically connected to the gate end of the fifth transistor  341 . The eighth transistor  344  comprises a first end electrically connected to the second end of the seventh transistor  343 , a gate end electrically connected to the second end of the first transistor  306 , and a second end for receiving the power voltage Vss. 
         [0027]    The eleventh transistor  361  comprises a first end for receiving the second clock LC 2 , a second end for outputting the second control signal SCn 2 , and a gate end electrically connected to the thirteenth transistor  363 . The twelfth transistor  362  comprises a first end electrically connected to the second end of the eleventh transistor  361 , a gate end electrically connected to the second end of the first transistor  306 , and a second end for receiving the power voltage Vss. The thirteenth transistor  363  comprises a first end for receiving the second clock LC 2 , a gate end for receiving the second clock LC 2 , and a second end electrically connected to the gate end of the eleventh transistor  361 . The fourteenth transistor  364  comprises a first end electrically connected to the second end of the thirteenth transistor  363 , a gate end electrically connected to the second end of the first transistor  306 , and a second end for receiving the power voltage Vss. The circuit operations regarding the fifth through eighth transistors  341 - 344  and the eleventh through fourteenth transistors  361 - 364  are well known to those skilled in the art and, for the sake of brevity, further discussion thereof is omitted. Other circuit functions of the Nth shift register stage  413  are similar to those of the Nth shift register stage  213 , and are not described again here. 
         [0028]      FIG. 5  is a schematic diagram showing a shift register circuit in accordance with a second embodiment of the present invention. As shown in  FIG. 5 , the shift register circuit  500  comprises a plurality of shift register stages and, for ease of explanation, illustrates an (N−2) th shift register stage  511 , an (N−1) th shift register stage  512 , an Nth shift register stage  513 , an (N+1)th shift register stage  514  and an (N+2)th shift register stage  515 . For the sake of brevity, only the internal structure of the Nth shift register stage  513  is exemplified in detail. The internal structures of other shift register stages are similar to the Nth shift register stage  513  and can be inferred by analogy. In the operation of the shift register circuit  500 , the Nth shift register stage  513  is utilized for performing a circuit operation with high driving ability to generate a gate signal SGn, a start pulse signal STn and a driving control voltage VQn according to a driving control voltage VQn−2 generated by the (N−2) th shift register stage  511 , a start pulse signal STn−1 generated by the (N−1) th shift register stage  512 , a gate signal SGn+2 generated by the (N+2) th shift register stage  515 , a first system clock HC 1 , a first clock LC 1 , a second clock LC 2  having a phase opposite to the first clock LC 1 , and a power voltage Vss. The circuit functions of other shift register stages are similar to the Nth shift register stage  513  and can be inferred by analogy. Regarding the system clocks HC 1 -HC 4  shown in  FIG. 5 , it is noted that the third system clock HC 3  has a phase opposite to the first system clock HC 1 , the second system clock HC 2  has a 90-degree phase difference relative to the first system clock HC 1 , and the fourth system clock HC 4  has a phase opposite to the second system clock HC 2 . 
         [0029]    As shown in  FIG. 5 , the Nth shift register stage  513  is similar to the Nth shift register stage  213  shown in  FIG. 2 , differing in that the input unit  305  is replaced with an input unit  505 , and a carry unit  520  is further added. The input unit  505  is electrically connected to the (N−1) th shift register stage  512  for receiving the start pulse signal STn−1, and is further electrically connected to the (N−2) th shift register stage  511  for receiving the driving control voltage VQn−2. The input unit  505  is utilized for outputting the driving control voltage VQn according to the start pulse signal STn−1 and the driving control voltage VQn−2. The carry unit  520 , electrically connected to the input unit  505 , is utilized for outputting the start pulse signal STn according to the driving control voltage VQn and the first system clock HC 1 . 
         [0030]    In the embodiment shown in  FIG. 5 , the input unit  505  comprises a first transistor  506 , and the carry unit  520  comprises a seventeenth transistor  521 . The first transistor  506  comprises a first end electrically connected to the (N−1) th shift register stage  512  for receiving the start pulse signal STn−1, a gate end electrically connected to the (N−2) th shift register stage  511  for receiving the driving control voltage VQn−2, and a second end for outputting the driving control voltage VQn. The seventeenth transistor  521  comprises a first end for receiving the first system clock HC 1 , a gate end electrically connected to the second end of the first transistor  506  for receiving the driving control voltage VQn, and a second end for outputting the start pulse signal STn. Since the waveform of the start pulse signal STn is substantially identical to that of the gate signal SGn, the circuit operation of the Nth shift register stage  513  is therefore similar to that of the Nth shift register stage  213  and, for the sake of brevity, further discussion thereof is not described again here. 
         [0031]    To sum up, in the operation of the shift register circuit according to the present invention, while pulling up one gate signal by a corresponding pull-up unit, the corresponding pull-up unit is driven by a driving control voltage of approximate twice the high-level voltage of system clock so as to achieve high output driving ability, thereby enhancing pixel charging rate for improving display quality. 
         [0032]    The present invention is by no means limited to the embodiments as described above by referring to the accompanying drawings, which may be modified and altered in a variety of different ways without departing from the scope of the present invention. Thus, it should be understood by those skilled in the art that various modifications, combinations, sub-combinations and alternations might occur depending on design requirements and other factors insofar as they are within the scope of the appended claims or the equivalents thereof.