# Patent

## Title
Shift register, liquid crystal display device having the shift register and method of driving scan lines using the same

## Abstract

In a bi-directional shift register and a liquid crystal display device having the bi-directional shift register, the shift register further includes a dummy stage for resetting a last stage. The dummy stage is reset by a control signal of the last stage or by the output signal of the dummy stage. Therefore, power consumption and layout area may be reduced. The shift register includes a plurality of stages and two dummy stages, and two selection signals for selecting shift direction is applied to each of the stages.

## Background
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a divisional application of U.S. application Ser. No. 10/458,053 filed Jun. 10, 2003, which claims priority to and the benefit of Korean Patent Application No. 2002-32368 filed on Jun. 10, 2002 and Korean Patent Application No. 2002-37944 filed on Jul. 2, 2002, the contents of which are herein incorporated by reference in their entirety.


BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a shift register, a liquid crystal display (LCD) device having the shift register and a method of driving scan lines using the same.
2. Description of the Related Art
An LCD device has advantages over other display devices, for example CRT type display device. In detail, the LCD device may be manufactured in a thinner and lighter structure having a lower power consumption, may require a lower driving voltage compared with the other display devices, and may provide image display quality similar to that of the CRT type display device. The LCD device is widely used in various electronic apparatus.
When voltage is applied to liquid crystal molecules, the alignment angle of the liquid crystal molecules is changed, the transmissivity of the liquid crystal molecules is regulated, and thus an image is displayed.
The LCD device is classified into a twisted nematic (TN) type LCD device and a super-twisted nematic (STN) type LCD device. The LCD device also may be classified into an active matrix type LCD device and a passive matrix type LCD device according to a method of driving the LCD device. The active matrix type LCD device employs switching elements and TN liquid crystal. The active matrix type LCD device is used in a thin film transistor (TFT) LCD device. However, the passive matrix type LCD device employs STN liquid crystal.
The active matrix type LCD device uses the thin film transistors as a switching element so as to drive the LCD device. However, the passive matrix type LCD device does not use transistors so as to drive the LCD device, so that the passive matrix type LCD device does not require complicated circuits for driving the LCD device.
The TFT LCD device is classified into amorphous-Si TFT LCD (or a-Si TFT LCD) device and a poly-Si TFT LCD device. The poly-silicon TFT LCD (or poly-Si TFT LCD) device has lower power consumption and a low price, but is manufactured through complex processes compared with the a-Si TFT LCD device. Accordingly, the poly-Si TFT LCD is used in a display device having a small display screen such as a mobile phone.
The a-Si TFT LCD device may provide a large display screen and a high yield (or high productivity), and is used in a display device having a large display screen such as a laptop computer, an LCD monitor or a high definition television (HDTV).
FIG. 1 is a schematic view showing a conventional poly-silicon thin film transistor LCD, and FIG. 2 is a schematic view showing a conventional a-Si thin film transistor LCD.
As shown in FIG. 1, the poly-Si TFT LCD device includes a poly-Si TFT pixel array formed on a glass substrate 10. A data driver circuit 12 and a gate driver circuit 14 are formed on the glass substrate 10. An integrated printed circuit board 20 is connected to a terminal part 16 by means of a film cable 18, so that the cost for manufacturing the poly-Si TFT LCD device may be reduced and power consumption may be minimized because the data driver circuit 12 and the gate driver circuit 14 are integrated on the glass substrate 10.
However, as shown in FIG. 2, in the a-Si TFT LCD device, a data driver chip 34 is mounted on a flexible printed circuit board 32 via a chip on film (COF), and a data printed circuit board 36 is connected to a data line terminal on the a-Si TFT pixel array through the flexible printed circuit board 32. A gate driver chip 40 is mounted on the flexible printed circuit board 32 via the chip on film (COF), and a gate printed circuit board 42 is connected to a gate line terminal on the a-Si TFT pixel array through a flexible printed circuit board 40.
The a-Si TFT LCD device has an advantage in aspect of yield (or productivity), but has disadvantage in aspect of manufacturing cost and thickness.
A power supply for supplying a power voltage to the gate driver circuit may be mounted on the data printed circuit board so as to remove the gate printed circuit board.
However, even when the gate driver circuit is mounted on the data printed circuit board, the gate driver circuit is mounted on the flexible printed circuit. Since a plurality of flexible printed circuits is bonded to the glass substrate, the a-Si TFT LCD device uses a complicate outer lead bonding process so as to bind the flexible printed circuits to the glass substrate. Accordingly, the cost for manufacturing the a-Si TFT LCD device increases.
Therefore, according to a recent method of manufacturing the a-Si TFT LCD device, the data driver circuit and the gate driver circuit are formed on the glass substrate in the same process as the process of forming the pixel array on the glass substrate so as to reduce the number of steps for manufacturing the a-Si TFT LCD device.
However, the shift direction is fixed in the shift register of the conventional a-Si TFT LCD device, and the conventional a-Si TFT LCD device does not provide a bi-directional shift register in which a forward shift or a backward shift occurs.
SUMMARY OF THE INVENTION
Accordingly, the present invention is provided to substantially obviate one or more problems due to limitations and disadvantages of the related art.
It is an aspect of the present invention to provide a shift register, which may drive a liquid crystal display device having a large display screen, may have low power consumption and may have a reduced layout area required for designing the shift register.
It is another aspect of the present invention to provide a liquid crystal display device having the shift register, which may drive the liquid crystal display device having a large display screen, may have low power consumption and may have a reduced layout area required for designing the shift register.
It is still another aspect of the present invention to provide a shift register having a bidirectional shift function so that an image may be displayed upside down on the display screen.
It is still another aspect of the present invention to provide a liquid crystal display device including the shift register having a bidirectional shift function so that an image may be displayed upside down on the display screen.
In one aspect of the present invention, there is provided a shift register including a plurality of stages and a dummy stage. The stages include odd numbered stages and even numbered stages. The odd numbered stages respectively receives a first clock and a first control signal, the first clock is prevented from being outputted from each of the odd numbered stages in response to the first control signal, and the even numbered stages respectively receives a second clock and a second control signal. The second clock is prevented from being outputted from each of the even numbered stages in response to the second control signal. The second clock has a first phase 180° different from a second phase of the first clock. The stages respectively delay the first clock or the second clock by a first period to sequentially output the first clock and the second clock as a scan line driving signal. The dummy stage generates a dummy output signal, and the scan line driving signal of a last stage falls below a first predetermined voltage level in response to the dummy output signal of the dummy stage. The dummy output signal is delayed by a second period and falls below a second predetermined voltage level in response to the dummy output signal.
In another aspect of the present invention, there is provided a shift register including a plurality of stages and a dummy stage. The stages include odd numbered stages and even numbered stages. The odd numbered stages respectively receives a first clock and a first control signal, the first clock is prevented from being outputted from each of the odd numbered stages in response to the first control signal, and the even numbered stages respectively receives a second clock and a second control signal. The second clock is prevented from being outputted from each of the even numbered stages in response to the second control signal. The second clock has a first phase 180° different from a second phase of the first clock. The stages respectively delay the first clock or the second clock by a first period to sequentially output the first clock and the second clock as a scan line driving signal. The dummy stage is coupled to a last stage and generates a dummy output signal. The scan line driving signal of the last stage falls below a first predetermined voltage level in response to the dummy output signal of the dummy stage, and the dummy output signal is delayed by a second period and falls below a second predetermined voltage level in response to a control signal of the last stage.
In further another aspect of the present invention, there is provided a liquid crystal display device including a display cell array, a data driver circuit and a gate driver circuit. The display cell array is formed on a transparent substrate and includes a plurality of gate lines, a plurality of data lines and a plurality of switching elements. The switching elements respectively are coupled to each of the data lines and each of the gate lines. The data driver circuit is coupled with the data lines and provides the data lines with image signals. The gate driver circuit is coupled with the gate lines and drives the switching elements. The gate driver circuit includes a plurality of stages and a dummy stage. The stages include odd numbered stages and even numbered stages, and the odd numbered stages respectively receives a first clock and a first control signal. The first clock is prevented from being outputted from each of the odd numbered stages in response to the first control signal. The even numbered stages respectively receive a second clock and a second control signal, and the second clock is prevented from being outputted from each of the even numbered stages in response to the second control signal. The second clock has a first phase 180° different from a second phase of the first clock. The stages respectively delay the first clock or the second clock by a first period and sequentially output the first clock and the second clock as a gate line driving signal to sequentially select the gate lines. The dummy stage generates a dummy output signal. The gate line driving signal of a last stage falls below a first predetermined voltage level in response to the dummy output signal of the dummy stage, and the dummy output signal is delayed by a second period, and falls below a second predetermined voltage level in response to the dummy output signal.
In still another aspect of the present invention, there is provided a liquid crystal display device including a display cell array, a data driver circuit and a gate driver circuit. The display cell array is formed on a transparent substrate, and the display cell array includes a plurality of gate lines, a plurality of data lines and a plurality of switching elements. The switching elements respectively are coupled to each of the data lines and each of the gate lines. The data driver circuit is coupled with the data lines and provides the data lines with image signals. The gate driver circuit is coupled with the gate lines and drives the switching elements. The gate driver circuit includes a plurality of stages and a dummy stage. The stages include odd numbered stages and even numbered stages. The odd numbered stages respectively receive a first clock and a first control signal. The first clock is prevented from being outputted from each of the odd numbered stages in response to the first control signal, and the even numbered stages respectively receive a second clock and a second control signal. The second clock is prevented from being outputted from each of the even numbered stages in response to the second control signal. The second clock has a first phase 180° different from a second phase of the first clock, and the stages respectively delay the first clock or the second clock by a first period to sequentially output the first clock and the second clock as a gate line driving signal. The dummy stage is coupled to a last stage and generates a dummy output signal. The gate line driving signal of the last stage falls below a first predetermined voltage level in response to the dummy output signal of the dummy stage, and the dummy output signal is delayed by a second period and falling below a second predetermined voltage level in response to a control signal of the last stage.
In still another aspect of the present invention, there is provided a method of driving a plurality of scan lines by providing a display panel with a plurality of scan line driving signals. A scan start signal is received so as to generate a first scan line driving signal, and a first voltage level of the first scan line driving signal is lowered so as to inactivate a first scan line in response to a second scan line driving signal. A (N−1)th scan line driving signal is received so as to generate a Nth scan line driving signal, and a second voltage level of the Nth scan line driving signal is lowered so as to inactivate a Nth scan line in response to an (N+1)th scan line driving signal. N is a natural number more than 2. A Mth scan line driving signal is generated in response to a (M−1)th scan line driving signal, and M is the integer greater than N and has a same number as a number of the scan lines. A control signal is generated in response to the Mth scan line driving signal, and a third voltage level of the Mth scan line driving signal is lowered so as to inactivate a Mth scan line. A fourth voltage level of the control signal is lowered after a predetermined period of delay in response to the control signal.
In still another aspect of the present invention, there is provided a method of driving a plurality of scan lines by providing a display panel with a plurality of scan line driving signals. A scan start signal is received so as to generate a first scan line driving signal, and a first voltage level of the first scan line driving signal is lowered so as to inactivate a first scan line in response to a second scan line driving signal. A (N−1)th scan line driving signal is received so as to generate a Nth scan line driving signal, and a second voltage level of the Nth scan line driving signal is lowered so as to inactivate a Nth scan line in response to an (N+1)th scan line driving signal. N is a natural number more than 2. A Mth scan line driving signal is generated in response to a (M−1)th scan line driving signal, and M is the integer greater than N and has a same number as a number of the scan lines. A dummy output signal is generated in response to the Mth scan line driving signal, and a third voltage level of the Mth scan line driving signal is lowered so as to inactivate a Mth scan line. The Mth scan line driving signal has a first voltage level. A fourth voltage level of the dummy output signal is lowered in response to a control signal, and the control signal has substantially the first voltage level.
In still another aspect of the present invention, there is provided a shift register including odd numbered stages and even numbered stages. The odd numbered stages respectively receive a first clock, and the even numbered stages respectively receive a second clock having a first phase 180° different from a second phase of the first clock. The shift register includes a first stage, an Nth stage (N is an integer greater than or equal to 2), a last stage, a first dummy stage and a second dummy stage. The first stage performs a forward shift from the first stage to a last stage when a first selection signal has a first voltage level and performs a backward shift from the last stage to the first stage when a second selection signal has the first voltage level. The Nth stage performs the forward shift from the first stage to the last stage when the first selection signal has the first voltage level and performs the backward shift from the last stage to the first stage when the second selection signal has the first voltage level. The last stage performs the forward shift from the first stage to the last stage when the first selection signal has the first voltage level and performs the backward shift from the last stage to the first stage when the second selection signal has the first voltage level. The first dummy stage inactivates (or reset) the last stage during the forward shift. A second dummy stage inactivates the first stage during the backward shift.
In still another aspect of the present invention, there is provided a shift register including odd numbered stages and even numbered stages. The odd numbered stages respectively receive a first clock, and the even numbered stages respectively receive a second clock having a first phase 180° different from a second phase of the first clock. The stages of the shifter register are sequentially shifted in synchronization with the first and second clock signals in a forward direction and in a backward direction. The shift register including a first stage, an Nth stage (N is an integer greater than or equal to 2), a last stage, a first dummy stage and a second dummy stage. The first stage receives a scan start signal, generates a first scan line driving signal when a first selection signal has a first voltage level, and lowers a second voltage level of the first scan line driving signal in response to a second scan line driving signal generated from a second stage. The first stage generates the first scan line driving signal in response to the second scan line driving signal when a second selection signal has the first voltage level, and lowers the second voltage level of the first scan line driving signal in response to a second dummy output signal. The Nth stage generates a Nth scan line driving signal in response to a (N−1)th scan line driving signal outputted from a (N−1)th stage when the first selection signal has the first voltage level, and lowers a third voltage level of the Nth scan line driving signal in response to an (N+1)th scan line driving signal outputted from an (N+1)th stage. The Nth stage generates the Nth scan line driving signal in response to the (N+1)th scan line driving signal when the second selection signal has the first voltage level, and lowers the third voltage level of the Nth scan line driving signal in response to the (N−1)th scan line driving signal. N is an integer greater than 2. A Mth stage generates a Mth scan line driving signal in response to a (M−1)th scan line driving signal outputted from a (M−1)th stage when the first selection signal has the first voltage level, and lowers a fourth voltage level of the Mth scan line driving signal in response to a first dummy output signal. The Mth stage generates the Mth scan line driving signal in response to the scan start signal when the second selection signal has the first voltage level, and lowers the fourth voltage level of the Mth scan line driving signal in response to the (M−1)th scan line driving signal. M is the integer greater than N. A first dummy stage receives the first clock signal and the Mth scan line driving signal to generate the first dummy output signal, and the first dummy stage lowers a fifth voltage level of the first dummy output signal in response to the scan start signal. The second dummy stage receives the second clock signal and the first scan line driving signal to generate the second dummy output signal, and the second dummy stage lowers a sixth voltage level of the second dummy output signal in response to the scan start signal.
In still another aspect of the present invention, there is provided a liquid crystal display device including a display cell array, a data driver circuit and a gate driver circuit. The display cell array is formed on a transparent substrate. The display cell array includes a plurality of gate lines, a plurality of data lines and a plurality of switching elements. The switching elements respectively are coupled to each of the data lines and each of the gate lines. The data driver circuit is coupled with the data lines and provides the data lines with image signals. A gate driver circuit includes odd numbered stages and even numbered stages. The odd numbered stages respectively receive a first clock, and the even numbered stages respectively receive a second clock having a first phase 180° different from a second phase of the first clock. The gate driver circuit includes a first stage, an Nth stage (N is an integer greater than or equal to 2), a last stage, a first dummy stage and a second dummy stage. The first stage performs a forward shift from the first stage to a last stage when a first selection signal has a first voltage level and performs a backward shift from the last stage to the first stage when a second selection signal has the first voltage level. The Nth stage performs the forward shift from the first stage to the last stage when the first selection signal has the first voltage level and performs the backward shift from the last stage to the first stage when the second selection signal has the first voltage level. The last stage performs the forward shift from the first stage to the last stage when the first selection signal has the first voltage level and performs the backward shift from the last stage to the first stage when the second selection signal has the first voltage level. The first dummy stage inactivates the last stage during the forward shift, and the second dummy stage inactivates the first stage during the backward shift.
In still another aspect of the present invention, there is provided a liquid crystal display device including a display cell array, a data driver circuit and a gate driver circuit. The display cell array is formed on a transparent substrate. The display cell array includes a plurality of gate lines, a plurality of data lines and a plurality of switching elements. The switching elements respectively are coupled to each of the data lines and each of the gate lines. The data driver circuit is coupled with the data lines and provides the data lines with image signals. The gate driver circuit includes odd numbered stages and even numbered stages. The odd numbered stages respectively receive a first clock, and the even numbered stages respectively receive a second clock having a first phase 180° different from a second phase of the first clock. The stages of the shifter register are sequentially shifted in synchronization with the first and second clock signals in a forward direction and in a backward direction. The gate driver circuit includes a first stage, an Nth stage (N is an integer greater than or equal to 2), an Mth stage (M is the integer greater than N), a last stage, a first dummy stage and a second dummy stage. The first stage receives a scan start signal to generate a first gate line driving signal when a first selection signal has a first voltage level and lowers a second voltage level of the first scan line driving signal in response to a second gate line driving signal generated from a second stage. The first stage generates the first gate line driving signal in response to the second gate line driving signal when a second selection signal has the first voltage level and lowers the second voltage level of the first gate line driving signal in response to a second dummy output signal. The Nth stage generates a Nth gate line driving signal in response to a (N−1)th gate line driving signal outputted from a (N−1)th stage when the first selection signal has the first voltage level and lowers a third voltage level of the Nth gate line driving signal in response to an (N+1)th gate line driving signal outputted from an (N+1)th stage. The Nth stage generates the Nth gate line driving signal in response to the (N+1)th gate line driving signal when the second selection signal has the first voltage level and lowers the third voltage level of the Nth gate line driving signal in response to the (N−1)th gate line driving signal.
The Mth stage generates a Mth gate line driving signal in response to a (M−1)th gate line driving signal outputted from a (M−1)th stage when the first selection signal has the first voltage level and lowers a fourth voltage level of the Mth gate line driving signal in response to a first dummy output signal. The Mth stage generates the Mth gate line driving signal in response to the scan start signal when the second selection signal has the first voltage level and lowers the fourth voltage level of the Mth gate line driving signal in response to the (M−1)th gate line driving signal. The first dummy stage receives the first clock signal and the Mth gate line driving signal to generate the first dummy output signal, and the first dummy stage lowers a fifth voltage level of the first dummy output signal in response to the scan start signal. The second dummy stage receives the second clock signal and the first gate line driving signal to generate the second dummy output signal. The second dummy stage lowers a sixth voltage level of the second dummy output signal in response to the scan start signal.
In still another aspect of the present invention, there is provided a liquid crystal display device including a first transparent substrate, a second transparent substrate facing the first transparent substrate, a liquid crystal layer interposed between the first and second transparent substrates, a display cell array, a gate driver circuit, a data driver circuit and a flexible printed circuit board. The display cell array is formed on the first transparent substrate. The display cell array includes a plurality of gate lines, a plurality of data lines and a plurality of first switching elements, and the first switching elements respectively are coupled to each of the data lines and each of the gate lines. The gate driver circuit is formed on the first transparent substrate and performs a bi-directional shift operation in which the gate lines are selected sequentially in a forward direction or in a backward direction. The gate driver circuit includes a plurality of stages, a first dummy stage and a second dummy stage. The first dummy stage lowers a first voltage level of a last gate line driving signal outputted from a last stage, and the second dummy stage lowers a second voltage level of a first gate line driving signal outputted from a first stage and inactivates the first dummy stage. The data driver circuit is formed on the first transparent substrate and provides the data lines an image signal. The date driver circuit includes a shift register and a plurality of data line blocks. The data line blocks respectively have a plurality of second switching elements, a first electrode of each of the second switching elements coupled to a data input terminal, second electrodes of the second switching elements coupled to respective data lines, third electrodes of the second switching elements commonly coupled to respective block selection terminals. The shift register has a plurality of data stages cascade-connected to each other, and a first data stage receives a scan start signal for initiating a selection of the data line blocks. The data stages outputs a block selection signal so as to sequentially select each of the data line blocks. The flexible printed circuit board provides the gate driver circuit and the data driver circuit with a control signal and the image signal, respectively. The flexible printed circuit includes a control integrated circuit and a data driver integrated circuit mounted thereon.
In still another aspect of the present invention, there is provided a method of driving a plurality of scan lines. The scan lines are sequentially selected in a forward shift from a first scan line to a last scan line or in a backward shift from the last scan line to the first scan line. In the forward shift, a first scan line driving signal is generated when a first selection signal has a first voltage level. In the backward shift, the first scan line driving signal is generated when a second selection signal has the first voltage level. In the forward shift, 2nd, 3rd, . . . , (N−1)th scan line driving signals are generated when the first selection signal has the first voltage level. In the backward shift, the 2nd, 3rd, . . . , (N−1)th scan line driving signals are generated when the second selection signal has the first voltage level, and N is an integer greater than 4. In the forward shift, an Nth scan line driving signal is generated when the first selection signal has the first voltage level. In the backward shift, the Nth scan line driving signal is generated when the second selection signal has the first voltage level. A first dummy output signal is generated during the forward shift to lower a second voltage level of the Nth scan line driving signal. A second dummy output signal is generated during the backward shift to lower a third voltage level of the first scan line driving signal.
In still another aspect of the present invention, there is provided a method of driving a plurality of scan lines. The scan lines are sequentially selected in a forward shift from a first scan line to a last scan line or in a backward shift from the last scan line to the first scan line. A first scan line driving signal is generated in response to a scan start signal, and a first voltage level of the first scan line driving signal is lowered in response to a second scan line driving signal so as to perform the forward shift when a first selection signal has a first level. The first scan line driving signal is generated in response to the second scan line driving signal, and the first voltage level of the first scan line driving signal is lowered in response to a second dummy output signal so as to perform the backward shift when a second selection signal has the first level. 2nd, 3rd, . . . , and (N−1)th scan line driving signals are generated in response to a previous scan line driving signal, and a second voltage level of each of the 2nd, 3rd, . . . , and (N−1)th scan line driving signals are lowered in response to a next scan line driving signal so as to perform the forward shift when the first selection signal has the first level. The 2nd, 3rd, . . . , and (N−1)th first scan line driving signals are generated in response to the next scan line driving signal, and the second voltage level of each of the 2nd, 3rd, . . . , and (N−1)th scan line driving signals are lowered in response to the previous scan line driving signal so as to perform the backward shift when the second selection signal has the first level, N being an integer greater than 4. A Nth scan line driving signal are generated in response to a (N−1)th scan line driving signal, and a third voltage level of the Nth scan line driving signal is lowered in response to the first dummy output signal so as to perform the forward shift when the first selection signal has the first level. The Nth scan line driving signal is generated in response to the scan start signal, and the third voltage level of the Nth scan line driving signal is lowered in response to the (N−1)th scan line driving signal so as to perform the backward shift when the second selection signal has the first level. The first dummy output signal is generated in response to the Nth scan line driving signal, and the third voltage level of the Nth scan line driving signal is lowered in response to the first dummy output signal during the forward shift. Then, a fourth voltage level of the first dummy output signal is lowered. The second dummy output signal is generated in response to the first scan line driving signal, and the first voltage level of the first scan line driving signal is lowered in response to the second dummy output signal during the backward shift. A fifth voltage level of the second dummy output signal is lowered.
As described above, according to the shift register of this invention, the shift register includes a plurality of stages and a dummy stage for resetting the last stage. the dummy stage is reset (or inactivated) by a control signal of the last stage or by the output signal of the dummy stage instead of the scan start signal. Since the output signal of the dummy stage does not exist during a display blanking period, the power consumption due to the output signal of the dummy stage may be reduced. In addition, since the dummy stage is reset not by the scan start signal, the layout area for gate driver circuit of the TFT LCD is reduced. In addition, the parasitic capacitance due to the scan start signal line may be reduced, the distortion of the signals may be reduced, and the power consumption of the first and second clocks due to the parasitic capacitance may be reduced.
Further, the shift register includes a plurality of stages and two dummy stages, and two selection signals for selecting shift direction is applied to each of the stages. The first and second clock signals ckv and ckvb may be alternately applied to the first and second clock terminals so as to change the shift direction. Accordingly, a bi-directional shift operation (forward or backward shift operation) may be performed without adding another circuits to the shift register.



BRIEF DESCRIPTION OF THE DRAWINGS
The above and other advantages of the present invention will become more apparent by describing in detail the preferred embodiments thereof with reference to the accompanying drawings, in which:
FIG. 1 is a schematic view showing a conventional poly-silicon thin film transistor LCD;
FIG. 2 is a schematic view showing a conventional a-Si thin film transistor LCD;
FIG. 3 is an exploded perspective view showing an a-Si thin film transistor LCD according to one exemplary embodiment of the present invention;
FIG. 4 is a schematic view showing an a-Si thin film transistor substrate of FIG. 3;
FIG. 5 is a block diagram showing a data driver circuit of FIG. 4;
FIG. 6 is a block diagram showing an Nth stage in a shift register of the gate driver circuit of FIG. 4;
FIG. 7 is a circuit diagram showing a stage of the shift register of FIG. 6;
FIG. 8 is a graph showing scan line driving signals outputted from the stage of FIG. 7;
FIG. 9 is a graph showing the scan line driving signals outputted from the shift register of FIG. 6;
FIG. 10 is a circuit diagram showing an Nth stage and an (N+1)th stage in the shift register of FIG. 7;
FIG. 11 is a graph showing the output of the shift register of FIG. 7;
FIG. 12 is a circuit diagram showing an Nth stage and an (N+1)th stage in a shift register according to one exemplary embodiment of the present invention;
FIG. 13 is a graph showing the output of the shift register of FIG. 12;
FIG. 14 is a circuit diagram showing an Nth stage and an (N+1)th stage in a shift register according to another exemplary embodiment of the present invention;
FIG. 15 is a graph showing the output of the shift register of FIG. 14;
FIG. 16 is a block diagram showing a bi-directional shift register employed in the gate driver circuit of an a-Si TFT LCD according to further another exemplary embodiment of the present invention;
FIG. 17 is a circuit diagram showing a second stage and a third stage in the shift register of FIG. 16;
FIG. 18 is a circuit diagram showing a dummy stage 0 in the shift register of FIG. 16;
FIG. 19 is a circuit diagram showing a first stage in the shift register of FIG. 16;
FIG. 20 is a circuit diagram showing a fourth stage in the shift register of FIG. 16;
FIG. 21 is a circuit diagram showing a dummy stage 1 in the shift register of FIG. 16;
FIG. 22 is a graph showing scan line driving signals outputted from the stages of FIG. 16 during a forward shift;
FIG. 23 is a graph showing scan line driving signals outputted from the stages of FIG. 16 during a backward shift;
FIG. 24 is a block diagram showing a bi-directional shift register employed in the gate driver circuit of an a-Si TFT LCD according to a still another exemplary embodiment of the present invention;
FIG. 25 is a circuit diagram showing a second stage and a third stage in the shift register of FIG. 24;
FIG. 26 is a circuit diagram showing a first stage in the shift register of FIG. 24;
FIG. 27 is a circuit diagram showing a fourth stage in the shift register of FIG. 24;
FIG. 28 is a graph showing scan line driving signals outputted from the stages of FIG. 24 during a forward shift;
FIG. 29 is a graph showing scan line driving signals outputted from the stages of FIG. 24 during a backward shift;
FIGS. 30, 31, 32 and 33 are block diagrams respectively showing a bi-directional shift register according to still another embodiment of the present invention; and
FIGS. 34, 35, 36 and 37 are block diagrams respectively showing a bi-directional shift register according to still another exemplary embodiment of the present invention.



DESCRIPTION OF EMBODIMENTS
Hereinafter the preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 3 is an exploded perspective view showing an a-Si thin film transistor LCD according to one exemplary embodiment of the present invention.
Referring to FIG. 3, the liquid crystal display device 100 includes a liquid crystal display panel assembly 110, a backlight assembly 120, a chassis 130 and a cover case 140.
The liquid crystal display panel assembly 110 includes a liquid crystal display panel 112, a flexible printed circuit board 116 and an integrated control chip 118. The liquid crystal display panel 112 includes a TFT substrate 112a and a color filter substrate 112b. 
A display cell array, a data driver circuit, a gate driver circuit and external connection terminals are formed on the TFT substrate 112a. Color filters and transparent common electrodes are formed on the color filter substrate 112b. The color filter substrate 112b faces the TFT substrate 112a, and liquid crystal is filled between the color filter substrate 112b and the TFT substrate 112a. 
The integrated control chip 118 is electrically connected to the thin film transistors formed on display cell array of the TFT substrate 112a through the flexible printed circuit 116. Data signal, data timing signal, gate timing signal and power voltage for driving the gate driver circuit is supplied to the data driver circuit and the gate driver circuit formed on the TFT substrate 112a. The display cell array includes a plurality of gate lines, a plurality of data lines and a plurality of switching elements, and the switching elements respectively is connected to each of the data lines and each of the gate lines. The gate driver circuit is connected with the gate lines, and drives the switching elements. The data driver circuit is connected with the data lines, and provides the data lines with image signals.
The backlight assembly 120 includes a lamp assembly 122, a light-guide plate 124, optical sheets 126, a reflection plate 128 and a mold frame 129.
FIG. 4 is a schematic view showing an a-Si thin film transistor substrate of FIG. 3.
Referring to FIG. 4, a display cell array 150, a data driver circuit 160, a gate driver circuit 170 and an external connection terminals 162 and 163 for connecting the data driver circuit 160 to the integrated control chip 118 and another external connection terminal 169 for connecting the gate driver circuit 170 to the integrated control chip 118 are formed on the TFT substrate 112a in the same process in which the TFTs are formed on the TFT substrate 112a. 
The display cell array 150 includes m data lines DL1, DL2, . . . , DLm and n gate lines GL1, GL2, . . . , GLn. The data lines DL1, DL2, . . . , DLm are extended in a column direction, and the gate lines GL1, GL2, . . . , GLn are extended in a row direction. For example, a liquid crystal display panel having 2-inch screen size is disclosed. The liquid crystal display panel has 176 data lines and 192 gate lines, to thereby provide a dot resolution 525 (176×3)×192.
Switching transistors (ST; or switching elements) are formed on an intersection between the data lines and the gate lines. A drain of the switching transistor STi is connected to a data line DLi, a gate of the switching transistor STi is connected to a gate line GLi, and a source of the switching transistor STi is connected to a pixel electrode PE. Liquid crystal LC is disposed between the pixel electrode PE and the common electrode CE. The common electrode CE is formed on the color filter substrate 112b. 
Therefore, the voltage applied to the pixel electrode PE and the common electrode CE changes the alignment angle of the liquid crystal molecules, the amount of the light that passing through the liquid crystal molecules are regulated, and an image may be displayed.
The data driver circuit 160 includes a shift register 164 and 528 switching transistors (SWTs). Each of 8 data line blocks BL1, BL2, . . . , BL8 includes 66 switching transistors (SWTs).
66 input terminals of each of the data line blocks are commonly connected to the external connection terminal 163, and 66 output terminals are connected to the 66 corresponding data lines, respectively. The external connection terminal 163 has 66 data input terminals. A block selection terminal is connected to an output terminal of the shift register 164.
Sources of the 528 switching transistors (SWTs) are connected to the corresponding data lines, drains of the 528 switching transistors (SWTs) are connected to the corresponding data input terminals, respectively, and the gates of the 528 switching transistors (SWTs) are connected to the block selection terminal. Each of the 528 switching transistors (SWTs) is a-Si TFT MOS transistor.
Accordingly, 66 data lines of the 528 data lines are divided into 8 blocks, and 8 block selection signals may sequentially select each of the blocks.
The shift register 164 receives a first clock CKH, a second clock CKHB and a block selection start signal STH through the external connection terminal 162 having three terminals. Each of the output terminals of the shift register 164 is connected to the block selection terminal of the corresponding data line block.
FIG. 5 is a block diagram showing a data driver circuit of FIG. 4.
Referring to FIG. 5, the shift register 164 according to the present invention includes, for example, 9 stages SRH1, SRH2, . . . , SRH9 that are cascade-connected with each other. An output terminal OUT of each of the stages is connected to the input terminal IN of a next stage. The stages includes 8 stages SRH1, SRH2, . . . , SRH8 and a dummy stage (SRC9). The 8 stages SRH1, SRH2, . . . , SRH8 correspond to the 8 data line blocks. Each of the stages includes an input terminal IN, an output terminal OUT, a control terminal CT, a clock terminal CK, a first power voltage terminal VSS and a second power voltage terminal VDD. The 8 stages SRH1, SRH2, . . . , SRH8 provide the block selection terminal of each of the data line blocks BL1, BL2, . . . , BL8 with the block selection start signals DE1, DE2, . . . , DE8, respectively. The block selection start signals DE1, DE2, . . . , DE8 is an enable signal for selecting each of the data line blocks.
The first clock CKH is applied to odd numbered stages SRH1, SRH3, SRH5, SRH7, and SRH9, and the second clock CKHB is applied to even numbered stages SRH2, SRH4, SRH6, SRH8. The first clock CKH has a phase 180° different from that of the second clock CKHB. For example, the duty period of the first clock CKH and the second clock CKHB is lower than 1/66 ms.
An output signal (or gate line driving signal) of the next stage is applied to a control terminal CT as a control signal.
The output signals of each of the stages have sequentially an active period (or a high level period), the data line block corresponding to the active period is selected.
The dummy stage SRH9 provides the control terminal CT of a previous stage (SRH8) with a control signal.
FIG. 6 is a block diagram showing an Nth stage in a shift register of the gate driver circuit of FIG. 4.
Referring to FIG. 6, the gate driver circuit 170 includes a shift register, and the shift register, a plurality of stages SRC1, SRC2, . . . , SRC192 and a dummy stage that are cascade-connected with each other. An output terminal OUT of each of the stages is connected to an input terminal IN of a next stage. The stages includes 192 stages SRC1, SRC2, . . . , SRC192 and a dummy stage.
Each of the stages includes an input terminal IN, an output terminal OUT, a control terminal CT, a clock signal input terminal CK, a first power voltage terminal VSS and a second power voltage terminal VDD.
The first stage SRC1 and the dummy stage receive a scan start signal STV. The scan start signal STV is a pulse synchronized with a vertical synchronization signal Vsync. Each of the stages SRC1, SRC2, . . . , SRC192 generates gate line driving signals GOUT1, GOUT2, . . . , GOUT192, respectively, and the gate line driving signals GOUT1, GOUT2, . . . , GOUT192 are connected to the gate lines, respectively, so as to select the gate lines.
A first clock ckv is applied to odd numbered stages (SRC1, SRC3, SRC5, . . . ), and the second clock ckvb is applied to even numbered stages (SRH2, SRH4, SRH6, . . . ). The first clock CKB has a phase 180° different from that of the second clock ckvb. For example, the duty period of the first clock ckv and the second clock ckvb is about 16.6/192 ms.
The duty period of the clock used in the shift register 164 of the data driver circuit is about 8 times larger than that of the clock used in the shift register 170 of the gate driver circuit.
Output signals GOUT1, GOUT2, . . . , GOUT192 of the next stage SRC2, SRC3, SRC4 is applied to control terminals CT of the stages SRC1, SRC2, SRC3, respectively, as a control signal.
The output signals of each of the stages have sequentially an active period (or a high level period), the gate line corresponding to the active period is selected.
The dummy stage resets (or inactivates) the last stage (SRH192). Specifically, the dummy stage lowers a voltage level of the output signal of the last stage (SRH192) from a high voltage level (HIGH) to a low voltage level (LOW).
FIG. 7 is a circuit diagram showing a stage of the shift register of FIG. 6, and FIG. 8 is a graph showing scan line driving signals outputted from the stage of FIG. 7.
Referring to FIG. 7, each of the stages of the shift resister 170 includes a pull-up part 171, a pull-down part 172, a pull-up driver part 173 and a pull-down driver part 174.
The pull-up part 171 includes a first NMOS transistor M1 of which a drain is connected to a clock signal input terminal CK, a gate is connected to a third node N3 and a source is connected to an output terminal GOUT[N].
The pull-down part 172 includes a second NMOS transistor M2 of which a drain is connected to an output terminal OUT, a gate is connected to a fourth node N4 and a source is connected to a first power voltage terminal VSS.
The pull-up driver part 173 includes a capacitor C and NMOS transistors M3, M4 and M5. The capacitor C is connected between the third node N3 and the output terminal GOUT[N]. The third NMOS Transistor M3 has a drain connected to a second power voltage VON, a gate connected to an output terminal GOUT[N−1] of a previous stage, and a source connected to the third node N3. Transistor M4 has a drain connected to the third node N3, a gate connected to the fourth node N4 and a source connected to the first power voltage VOFF. Transistor M5 has a drain connected to the third node N3, a gate connected to the fourth node N4 and a source connected to the first power voltage VOFF. Transistor M3 has a transistor size about two times larger than that of transistor M5.
The pull-down driver part 174 includes two NMOS transistors M6 and M7. Transistor M6 has a drain and a gate commonly connected with each other to be connected to the second power voltage VON, a source connected to the fourth node N4. Transistor M7 has a drain connected to the fourth node N4, a gate connected to the third node N3 and a source connected to the first power voltage VOFF. Transistor M7 has a transistor size about sixteen times larger than that of transistor M6.
As shown in FIG. 8, when first and second clock signals ckv and ckvb and scan start signal STV are supplied to the shift register 170, the first stage SRC1 delays a high level period of the first clock signal ckv in response to the front (leading) edge of the scan start signal STV for a predetermined time of Tdr1, to thereby output a delayed output signal GOUT1.
As described above, the shift register formed on the glass substrate receives the scan start signal STV, the first clock ckv and the second clock ckvb, and drives the gates of the TFTs formed on the TFT substrate.
Hereinafter, the operation of each of the stages of the shift register is described.
FIG. 9 is a graph showing the scan line driving signals outputted from the shift register of FIG. 6.
Referring to FIG. 9, the shift register receives a first clock signal ckv or a second clock signal ckvb and sequentially provides a plurality of gate lines with a plurality of gate line driving signal (GOUT1, GOUT2, GOUT3, . . . ). The second clock ckvb has a phase 180° different from the phase of the first clock ckv. The first and second clock signals swings in a period of 2H, as shown in FIG. 9. A signal outputted from a timing controller (not shown) has a voltage in a range from 0 volt to 3 volts and is amplified to have a voltage in a range from −8 volts to 24 volts, so that the first and second clock signals is acquired.
Referring again to FIG. 7, the output signal (or gate line driving signal) GOUTN−1 of the previous stage charges the capacitor C and set (or activate) the present stage. The output signal (or gate line driving signal) GOUTN+1 of the next stage discharges the capacitor C and reset (or inactivate) the present stage.
When the first clock signal ckv, the second clock signals ckvb and the scan start signal STV are applied to the first stage, a high level period of the first clock signal ckv is delayed by a predetermined period in response to an rising edge of the scan start signal STV to be outputted at the output terminal as an output signal GOUT[1].
The capacitor C begins to be charged in response to the rising edge of the scan start signal STV that is inputted into the gate of the transistor M1 through the input terminal IN. When the voltage Vc1 charged at the capacitor C is larger than the threshold voltage of the transistor M1, the pull-up transistor M1 is turned on, and the high level period of the first clock signal ckv is outputted at the output terminal OUT.
When the high level period of the first clock signal CKV is outputted at the output terminal OUT, this output voltage, or the high level period of the first clock signal ckv, is bootstrapped at the capacitor C and thereby the gate voltage of the pull-up transistor M1 rises over the turn-on voltage Von. Accordingly, the NMOS pull-up transistor M1 maintains a full turn-on state. The transistor M1 is turned on even when the transistor M3 is turned on by the scan start signal STV since a transistor size of the transistor M3 is about 2 times larger than that of the transistor M4.
Meanwhile, the voltage of the fourth node N4 rises to the second power voltage Von by the transistor M6 before the scan start signal STV is inputted into the third node N3, and the transistor M2 is turned on. Accordingly, the output signal of the output terminal OUT has substantially the first power voltage Voff. When the scan start signal STV is inputted to the third node N3, the transistor M7 is turned on, and the voltage of the fourth node N4 is dropped to substantially the first power voltage Voff. Since the transistor size of the transistor M7 is about 16 times larger than that of the transistor M6, the fourth node N4 maintains substantially the first power voltage Voff even though the transistor M6 is turned on. Accordingly, the pull-down transistor M2 is turned off.
When the scan start signal STV is applied to the third node N3, the pull-down transistor M2 is turned off, and the first clock signal ckv is delayed by a duty period of the first clock signal ckv to be outputted at the output terminal.
When the voltage of the output signal outputted from the output terminal OUT is dropped to a turn-off voltage Voff (or Vss), the transistor M7 is turned off. Since only the second power voltage Von is provided to the fourth node N4 through the transistor M6, the voltage of the fourth node N4 begins to rise from a first power voltage Voff to a second power voltage Von. When the voltage of the fourth node begins to rise, the transistor M4 is turned on, and the charges at the capacitor are discharged through the transistor M4. Therefore, the pull-up transistor M1 begins to be turned off.
Then, since the output signal GOUT[N+1] outputted from the next stage rises to the turn-on voltage Von, the transistor M5 is turned on. Since the transistor size of the transistor M5 is about 2 times larger than that of the transistor M4, the voltage of the third node N3 is dropped to the first power voltage Voff more rapidly compared with the case in which only the transistor M4 is turned on.
In addition, when the voltage of the fourth node N4 rises to the second power voltage Von, the pull-down transistor M2 is turned on, and the output voltage outputted from the output terminal OUT is changed from the turn-on voltage Von to the turn-off voltage Voff.
Since the fourth node N4 is connected to the transistor M6, the fourth node N4 maintains the second power voltage Von even though the output signal GOUT[N+1] of the next stage that is applied to the control terminal CT is dropped to a low voltage level and the transistor M5 is turned off. Accordingly, the malfunction due to the turn-off of the pull-down transistor M2 is prevented. As shown in FIG. 8, the output signals GOUT[1], GOUT[2], GOUT[3], GOUT[4], . . . are sequentially generated.
As described above, the capacitor C is charged in response to the output signal of the previous stage, the clock signal applied to the pull-up part or pull-down part is outputted as an output signal of the present stage. When the output signal of the next stage is generated at the gate line connected to the output terminal of the next stage, the output signal of the next stage turns on the discharge transistor M5 and discharges the capacitor C, to thereby terminate an operation cycle of the shift register.
According to above described shift register, since the present stage is reset by the output signal of the next stage, the shift register requires at least one dummy stage for resetting the last stage. However, the dummy stage should be also reset.
As shown in FIG. 10, the scan start signal STV may be connected to the discharge transistor M5 of the dummy stage so as to reset the dummy stage.
FIG. 10 is a circuit diagram showing an Nth stage and an (N+1)th stage in the shift register of FIG. 7, and especially shows the connection between the last stage and the dummy stage.
As shown in FIG. 10, the discharge transistor M5 for discharging the capacitor C is discharged by the scan start signal STV, or the dummy stage is reset by the scan start signal STV.
FIG. 11 is a graph showing the output of the shift register of FIG. 7, especially shows the output of the shift register when the shift register has five stages and a dummy stage. The output signal of the dummy stage is not related with a gate line driving signal.
Referring to FIG. 11, the voltage of first clock signal ckv is changed to a high level in response to the rising edge of the scan start signal STV after a predetermined period of delay, and then the first gate line driving signal GOUT[1] is generated at the output terminal of the first stage.
Next, the gate line driving signals GOUT[2], GOUT[3], GOUT[4] and GOUT[5] are sequentially generated at the output terminals of the first, second, third, fourth and fifth stages, respectively. Since the scan start signal STV is applied to the first stage and the dummy stage (or the sixth stage), the dummy stage outputs the second clock signal ckvb before the dummy stage is reset by the next scan start signal STV.
However, when the dummy stage is reset by the scan start signal STV, the layout area for gate driver circuit of the TFT LCD increases since the scan start signal line is connected to the first stage and the sixth stage to be extended along the entire stages.
In addition, since the scan start signal line is arranged in a column direction and overlaps with the other wirings arranged in a row direction, the parasitic capacitance between the scan start signal line and the other wirings may increase, so that the distortion of the signals may occur.
Since the first and second clock signals ckv and ckvb discharge and charge the parasitic capacitance, the power consumption increases. The output signal of the dummy stage exists during display blanking period in which image display does not occur, to thereby increase the power consumption.
FIG. 12 is a circuit diagram showing an Nth stage and an (N+1)th stage in a shift register according to one exemplary embodiment of the present invention, and FIG. 13 is a graph showing the output of the shift register of FIG. 12.
Referring to FIG. 12, each of the stages of the shift register includes a pull-up part 171, a pull-down part 172, a pull-up driver part 173 and a pull-down driver part 174. In FIG. 12, the same reference numerals denote the same elements in FIG. 7, and thus the detailed descriptions of the same elements will be omitted.
The output of the pull-down driver part 174 of the last stage is connected to the pull-down part 172 of the last stage and also is connected to the pull-up driver part 173 of the dummy stage.
Particularly, the source of the sixth transistor M6 is connected to the gate of the fifth transistor M5 of the dummy stage.
The output of an inverter (transistors M6 and M7) has a low voltage level while the Nth stage (the last stage) outputs the Nth gate line driving signal GOUT[N]. The output voltage of the inverter is changed to a high voltage level when the Nth stage is reset (or inactivated) by the (N+1)th gate line driving signal GOUT[N+1]. The high level output voltage of the inverter turns on the fifth transistor M5 of the pull-up driver part 173 of the dummy stage and resets the dummy stage.
Referring to FIG. 13, the output signals GOUT[1], GOUT[2], GOUT[3], GOUT[4] and GOUT[5] is generated. The output signal GOUT[6] of the dummy stage resets the last stage, and then the voltage of GOUT[6] is dropped (or lowered).
Since the output signal of the dummy stage does not exist during the display blanking period, the power consumption may be reduced. Namely, the output signal of the dummy stage exists during the display blanking period in FIG. 11, but the output signal of the dummy stage does not exist during the display blanking period in FIG. 13, so that the power consumption due to the output signal of the dummy stage may be reduced.
In addition, since the dummy stage is reset not by the scan start signal STV, the layout area for gate driver circuit of the TFT LCD is reduced.
In addition, the parasitic capacitance due to the scan start signal line may be reduced, so that the distortion of the signals may be reduced and the power consumption of the first and second clocks due to the parasitic capacitance may be reduced.
In FIG. 10, since the scan start signal line is connected to the first stage and is also connected to the sixth stage so as to reset the dummy stage, another layout area is required, and overlap between the scan start signal line and the other wirings exists.
However, as shown in FIG. 12, since the dummy stage is reset by the output signal of the inverter of the last stage, the layout area may be reduced, and the overlap between wirings may be reduced.
FIG. 14 is a circuit diagram showing an Nth stage and an (N+1)th stage in a shift register according to another exemplary embodiment of the present invention, and FIG. 15 is a graph showing the output of the shift register of FIG. 14.
Referring to FIG. 14, each of the stages of the shift register according to another exemplary embodiment of the present invention includes a pull-up part 171, a pull-down part 172, a pull-up driver part 173 and a pull-down driver part 174. In FIG. 14, the same reference numerals denote the same elements in FIG. 7, and thus the detailed descriptions of the same elements will be omitted.
The output of the pull-up part 171 of the dummy stage is connected to the discharge transistor M5 of the pull-up driver part 173 of the last stage so as to reset the last stage, and also is connected to the pull-up driver part 173 of the dummy stage so as to reset the dummy stage.
Particularly, the source of the first transistor M1 of the dummy stage, or the drain of the second transistor M2 of the dummy stage is connected to the gate of the fifth transistor M5 of the last stage and also is connected to the gate of the fifth transistor M5 of the dummy stage.
The output signal of the dummy stage turns on the fifth transistor M5 of the discharge transistor M5 of the dummy stage and resets the dummy stage.
Referring to FIG. 15, the output signals GOUT[1], GOUT[2], GOUT[3], GOUT[4] and GOUT[5] is generated. The output signal GOUT[6] of the dummy stage resets the last stage, and then the voltage of GOUT[6] is dropped (or lowered).
Since the output signal of the dummy stage does not exist during the display blanking period, the power consumption may be reduced. Namely, the output signal of the dummy stage exists during the display blanking period in FIG. 11, but the output signal of the dummy stage does not exist during the display blanking period in FIG. 15, so that the power consumption due to the output signal of the dummy stage may be reduced.
In addition, since the dummy stage is reset not by the scan start signal STV, the layout area for gate driver circuit of the TFT LCD is reduced.
In addition, the parasitic capacitance due to the scan start signal line may be reduced, so that the distortion of the signals may be reduced and the power consumption of the first and second clocks due to the parasitic capacitance may be reduced.
In FIG. 10, since the scan start signal line is connected to the first stage and is also connected to the sixth stage so as to reset the dummy stage, another layout area is required, and overlap between the scan start signal line and the other wirings exists.
However, as shown in FIG. 14, since the dummy stage is reset by the output signal of the dummy stage, the layout area may be reduced, and the overlap between wirings may be reduced.
The shift direction of the output signal GOUT[1], GOUT[2], GOUT[3] and GOUT[4] is fixed in the shift register of FIGS. 6 and 7, and the a-Si TFT LCD device using the shift register of FIGS. 6 and 7 does not provide a forward shift function or a backward shift function. Namely, the a-Si TFT LCD device using the shift register of FIGS. 6 and 7 may not display images upside down on the display screen since the forward shift function and the backward shift function is not provided.
FIG. 16 is a block diagram showing a bi-directional shift register employed in the gate driver circuit of an a-Si TFT LCD according to further another exemplary embodiment of the present invention.
Referring to FIG. 16, the shift register includes a dummy stage 0 and a dummy stage 1. The dummy stage 0 is connected to the first stage. In addition, a first selection signal Vbuf and a second selection signal Vdis are used so as to select the shift direction.
The dummy stage 0 generates a dummy output signal (or a first reset control signal) for resetting the first stage SRC1 when the shift direction is changed to a backward shift.
When a second power voltage Von is applied to the first selection terminal Vbuf, a first power voltage Voff is applied to the second selection terminal Vdis, a first clock signal ckv is applied to a first clock terminal CKV and a second clock signal ckvb is applied to a second clock terminal CKVB, the forward shift operation occurs. In the forward shift operation, the gate line driving signals GOUT[1], GOUT[2], GOUT[3] and GOUT[4] are sequentially generated in the named order.
In addition, when a first power voltage Voff is applied to the first selection terminal Vbuf, a second power voltage Von is applied to the second selection terminal Vdis, the second clock signal ckvb is applied to the first clock terminal CKV and a first clock signal ckv is applied to the second clock terminal CKVB, the backward shift operation occurs. In the backward shift operation, the gate line driving signals GOUT[4], GOUT[3], GOUT[2] and GOUT[1] are sequentially generated in the named order.
Since the a-Si TFT LCD device uses NMOS transistors, the high voltage level of the first and second selection signals Vbuf and Vdis need to be larger than the maximum voltage of the first and second clock signals ckv and ckvb. The first and second selection signals Vbuf and Vdis are complementary each other, and the first and second clocks ckv and ckvb are complementary each other. Namely, the second selection signal Vdis has a phase 180° different from that of the first selection signal Vbuf, and the first clock signal ckv has a phase 180° different from that of the second clock signal ckvb. The first and second clock signals ckv and ckvb may be alternately applied to the first and second clock terminals CKV and CKVB so as to change the shift direction.
FIG. 17 is a circuit diagram showing a second stage and a third stage in the shift register of FIG. 16, and FIG. 18 is a circuit diagram showing a dummy stage 0 in the shift register of FIG. 16. FIG. 19 is a circuit diagram showing a first stage in the shift register of FIG. 16, and FIG. 20 is a circuit diagram showing a fourth stage in the shift register of FIG. 16. FIG. 21 is a circuit diagram showing a dummy stage 1 in the shift register of FIG. 16.
Referring to FIG. 17, in the second and third stage, the first selection terminal Vbuf is connected to a drain of transistor M3, and the second selection terminal Vdis is connected to a source of transistor M5 so as to provide the forward shift function or the backward shift function.
The forward shift operation occurs when the first selection signal Vbuf has a high voltage level (HIGH) and the first clock signal ckv is applied to the clock terminal CKV. Namely, the Nth stage is set (or activated) by the output signal GOUT[N−1] of the previous stage, and is reset (or inactivated) by the output signal GOUT[N+1] of the next stage.
The backward shift operation occurs when the second selection signal Vdis has a high voltage level (HIGH) and the second clock signal ckvb is applied to the clock terminal CKV. Namely, the Nth stage is set (or activated) by the output signal GOUT[N+1] of the next stage, and is reset (or inactivated) by the output signal GOUT[N−1] of the previous stage. The first and second selection signals Vbuf and Vdis are complementary each other
Referring to FIG. 19, in the first stage, transistors M8 and M9 is connected to a gate of the buffer transistor M3.
The first selection signal Vbuf is applied to the gate of the transistor M8 so as to select the scan start signal STV, and the second selection signal Vdis is applied to the gate of the transistor M9 so as to select a dummy 0 signal, or the output signal of the dummy stage 0.
The forward shift operation occurs when the first selection signal Vbuf has a high voltage level (HIGH) and the first clock signal ckv is applied to the clock terminal CKV. Namely, the first stage is set (or activated) by the scan start signal STV, and is reset (or inactivated) by the output signal GOUT[2] of the next stage.
The backward shift operation occurs when the second selection signal Vdis has a high voltage level (HIGH) and the second clock signal ckvb is applied to the clock terminal CKV. Namely, the first stage is set (or activated) by the output signal GOUT[2] of the next stage, and is reset (or inactivated) by the dummy 0 signal, or the output signal of the dummy stage 0. The first and second selection signals Vbuf and Vdis are complementary each other.
Referring to FIG. 20, in the fourth stage (or a last stage), transistors M10 and M11 are connected to a gate of a discharge transistor M5.
The first selection signal Vbuf is applied to the gate of the transistor M11 so as to select the dummy 1 signal, or the output signal of the dummy stage 1, and the second selection signal Vdis is applied to the gate of the transistor M10 so as to select the scan start signal STV.
The forward shift operation occurs when the first selection signal Vbuf has a high voltage level (HIGH) and the second clock signal ckvb is applied to the clock terminal CKV. Namely, the fourth stage is set (or activated) by the output signal GOUT[3] of the previous stage, and is reset (or inactivated) by the dummy 1 signal, or the output signal of the dummy stage 1.
The backward shift operation occurs when the second selection signal Vdis has a high voltage level (HIGH) and the first clock signal ckv is applied to the clock terminal CKV. Namely, the fourth stage is set (or activated) by the scan start signal STV, and is reset (or inactivated) by the output signal GOUT[3] of the previous stage. The first and second selection signals Vbuf and Vdis are complementary each other.
Referring to FIG. 21, in the dummy stage 1, the output signal GOUT[4] of the previous stage is applied to a gate of the buffer transistor M3, the power terminal Von is connected to a drain of the transistor M3, the scan start signal STV is applied to a gate of the transistor M5, and the power terminal Voff is connected to a source of the transistor M5.
When the first clock signal ckv is applied to the clock terminal CKV, the dummy stage 1 is set by the output signal GOUT[4] of the previous stage, and is reset by the scan start signal STV.
The dummy stage 1 outputs the dummy 1 signal to the drain of the transistor M11 of the fourth stage and resets the last stage (SRC4) during the forward shift operation.
Referring to FIG. 18, in the dummy stage 0, the output signal GOUT[1] of the next stage, or the first stage, is applied to a gate of the buffer transistor M3, the power terminal Von is connected to a drain of the transistor M3, the scan start signal STV is applied to a gate of the transistor M5, and the power terminal Voff is connected to a source of the transistor M5.
When the first clock signal ckvb is applied to the clock terminal CKV, the dummy stage 0 is set by the output signal GOUT[1] of the next stage, and is reset by the scan start signal STV.
The dummy stage 0 outputs the dummy 0 signal to the drain of the transistor M9 of the first stage and resets the first stage (SRC1) during the backward shift operation.
FIG. 22 is a graph showing scan line driving signals outputted from the stages of FIG. 16 during a forward shift. When Vbuf=Von, Vdis=Voff, CKV=ckv and CKVB=ckvb, the forward shift operation occurs. The second clock signal ckv has a phase 180° different from that of the first clock signal ckvb.
Referring to FIG. 22, the voltage of the first clock signal ckv is changed to a high level in response to the rising edge of the scan start signal STV after a predetermined period (t1) of delay, and then the first gate line driving signal GOUT[1] is generated at the output terminal of the first stage.
Next, the gate line driving signals GOUT[2], GOUT[3] and GOUT[4] are sequentially generated at the output terminals of the first, second, third and fourth stages, respectively.
FIG. 23 is a graph showing scan line driving signals outputted from the stages of FIG. 16 during a backward shift. When Vbuf=Voff, Vdis=Von, CKV=ckvb and CKVB=ckv, the backward shift operation occurs.
Referring to FIG. 23, the voltage of the first clock signal ckv is changed to a high level in response to the rising edge of the scan start signal STV after a predetermined period (t2) of delay, and then the fourth gate line driving signal GOUT[4] is generated at the output terminal of the fourth stage.
Next, the gate line driving signals GOUT[3], GOUT[2] and GOUT[1] are sequentially generated at the output terminals of the first, second, third and fourth stages, respectively.
FIG. 24 is a block diagram showing a bi-directional shift register employed in the gate driver circuit of an a-Si TFT LCD according to a still another exemplary embodiment of the present invention.
Referring to FIG. 24, the dummy stage 0 is connected to the first stage. In addition, a third selection signal VSEL1 and a fourth selection signal VSEL2 are used so as to select the shift direction. The third and fourth selection signals VSEL1 and VSEL2 are applied to each of the stages through transistors M8, M9, M10 and M11.
The high voltage level of the third and fourth selection signals VSEL1 and VSEL2 need to be larger than the maximum voltage of the first and second clock signals ckv and ckvb. The third and fourth selection signals VSEL1 and VSEL2 are complementary each other, and the first and second clock signals ckv and ckvb are complementary each other. The first and second clock signals ckv and ckvb may be alternately applied to the first and second clock terminals CKV and CKVB so as to change the shift direction.
When the second power voltage Von is applied to the third selection terminal VSEL1, the first power voltage Voff is applied to the fourth selection terminal VSEL2, the first clock signal ckv is applied to the first clock terminal CKV and the second clock signal ckvb is applied to the second clock terminal CKVB, the forward shift operation occurs. In the forward shift operation, the gate line driving signals GOUT[1], GOUT[2], GOUT[3] and GOUT[4] are sequentially generated in the named order.
In addition, when the first power voltage Voff is applied to the third selection terminal VSEL1, the second power voltage Von is applied to the fourth selection terminal VSEL2, the second clock signal ckvb is applied to the first clock terminal CKV and a first clock signal ckv is applied to the second clock terminal CKVB, the backward shift operation occurs. In the backward shift operation, the gate line driving signals GOUT[4], GOUT[3], GOUT[2] and GOUT[1] are sequentially generated in the named order.
FIG. 25 is a circuit diagram showing a second stage and a third stage in the shift register of FIG. 24, FIG. 26 is a circuit diagram showing a first stage in the shift register of FIG. 24, and FIG. 27 is a circuit diagram showing a fourth stage in the shift register of FIG. 24.
Transistors M8 and M9 are connected to a drain of transistor M3, and transistors M10 and M11 are connected to a gate of transistor M5.
The third selection terminal VSEL1 is connected to gates of transistor M8 and M11, and the fourth selection terminal VSEL2 is connected to gates of transistor M9 and M10.
Referring to FIG. 25, in the second and third stages, the forward shift operation occurs when the third selection signal VSEL1 has a high voltage level (HIGH). Namely, the Nth stage is set (or activated) by the output signal GOUT[N−1] of the previous stage. The output signal GOUT[N−1] of the previous stage is selected by transistor M8. The Nth stage is reset (or inactivated) by the output signal GOUT[N+1] of the next stage. The output signal GOUT[N+1] of the next stage is selected by transistor M11.
The backward shift operation occurs when the fourth selection signal VSEL2 has a high voltage level (HIGH). Namely, the Nth stage is set (or activated) by the output signal GOUT[N+1] of the next stage. The output signal GOUT[N+1] of the next stage is selected by transistor M9. The Nth stage is reset (or inactivated) by the output signal GOUT[N−1] of the previous stage. The output signal GOUT[N−1] of the previous stage is selected by transistor M10. Namely, the third and fourth selection signal VSEL1 and VSEL2 determines the shift direction.
Referring to FIG. 26, in the first stage, the scan start signal STV is applied to a drain of transistor M8, a dummy 0 signal, or the output signal of the dummy stage 0, is applied to a transistor M10.
The third selection signal VSEL1 is applied to the gates of transistors M8 and M11 so as to select the scan start signal STV and GOUT[2] signal, and the fourth selection signal VSEL2 is applied to the gates of transistors M9 and M10 so as to select a dummy 0 signal and GOUT[2].
The forward shift operation occurs when the third selection signal VSEL1 has a high voltage level (HIGH) and the first clock signal ckv is applied to the clock terminal CK. Namely, the first stage is set (or activated) by the scan start signal STV, and is reset (or inactivated) by the output signal GOUT[2] of the next stage.
The backward shift operation occurs when the fourth selection signal VSEL2 has a high voltage level (HIGH) and the second clock signal ckvb is applied to the clock terminal CK. Namely, the first stage is set (or activated) by the output signal GOUT[2] of the next stage, and is reset (or inactivated) by the dummy 0 signal, or the output signal of the dummy stage 0.
Referring to FIG. 27, in the fourth stage (or a last stage), the third selection signal VSEL1 is applied to the gates of transistors M8 and M11 so as to select GOUT[3] and the dummy 1 signal, and the fourth selection signal VSEL2 is applied to the gates of transistors M9 and M10 so as to select the scan start signal STV and GOUT[3]. The dummy 1 signal, or the output signal of the dummy stage 1, is used to provide the backward shift function.
The forward shift operation occurs when the third selection signal VSEL1 has a high voltage level (HIGH) and the second clock signal ckvb is applied to the clock terminal CK. Namely, the fourth stage is set (or activated) by the output signal GOUT[3] of the previous stage, and is reset (or inactivated) by the dummy 1 signal, or the output signal of the dummy stage 1.
The backward shift operation occurs when the fourth selection signal VSEL2 has a high voltage level (HIGH) and the first clock signal ckv is applied to the clock terminal CK. Namely, the fourth stage is set (or activated) by the scan start signal STV, and is reset (or inactivated) by the output signal GOUT[3] of the previous stage.
The dummy stage 0 and the dummy stage 1 has the same circuit structure as that of the dummy stage 0 and the dummy stage 1 of FIGS. 18 and 21.
FIG. 28 is a graph showing scan line driving signals outputted from the stages of FIG. 24 during a forward shift.
When VSEL1=Von, VSEL2=Voff, CKV=ckv and CKVB=ckvb, the forward shift operation occurs. The second clock signal ckv has a phase 180° different from that of the first clock signal ckvb.
FIG. 29 is a graph showing scan line driving signals outputted from the stages of FIG. 24 during a backward shift.
When VSEL1=Voff, VSEL2=Von, CKV=ckvb and CKVB=ckv, the backward shift operation occurs.
FIGS. 30, 31, 32 and 33 are block diagrams respectively showing a bi-directional shift register according to still another embodiment of the present invention. A dummy stage 0 and a dummy stage 1 are reset by the output signals of the first stage or the last stage instead of the scan start signal STV in order to prevent the output signals of the dummy stage 0 and the dummy stage 1 from existing during the display blanking period. FIG. 30 shows the connection between the dummy stage 0 and the first stage of FIG. 19, and FIG. 31 shows the connection between the dummy stage 0 and the first stage of FIG. 26. FIG. 32 shows the connection between the dummy stage 1 and the last stage of FIG. 20, and FIG. 33 shows the connection between the dummy stage 1 and the last stage of FIG. 27.
Referring to FIG. 30 and FIG. 31, a gate of a pull-down transistor M2 of the first stage is connected to the output of an inverter (M6 and M7) of the first stage, and is connected to a hold transistor M5 of the dummy stage 0 through a transistor M13 of the dummy stage 0.
In the dummy stage 0, the forward shift operation occurs when Vbuf=Von, Vdis=Voff. The dummy stage 0 is set (or activated) by the scan start signal STV inputted through the transistor M12 of the dummy stage 0, and is reset (or inactivated) by the output signal GOUT[1] of the first stage. The backward shift operation occurs when Vbuf=Voff, Vdis=Von. The dummy stage 0 is set (or activated) by the output signal GOUT[1] of the first stage, and is reset (or inactivated) by the output signal of the inverter of the first stage.
Accordingly, in the backward shift operation, the dummy stage 0 is reset by a control signal, or the output of the inverter of the first stage instead of the scan start signal STV, to thereby prevent the output signal of the dummy stage 0 from remaining during the display blanking period.
Referring to FIG. 32 and FIG. 33, a gate of a pull-down transistor M2 of the last stage is connected to the output of an inverter (M6 and M7) of the last stage, and is connected to a hold transistor M5 of the dummy stage 1 through a transistor M13 of the dummy stage 1.
In the dummy stage 1, the forward shift operation occurs when Vbuf=Von, Vdis=Voff. The dummy stage 1 is set (or activated) by the output signal GOUT[4] of the last stage, and is reset (or inactivated) by the output of the inverter (M6 and M7) of the last stage. The backward shift operation occurs when Vbuf=Voff, Vdis=Von. The dummy stage 1 is set (or activated) by the scan start signal STV inputted through transistor M14 of the dummy stage 1, and is reset (or inactivated) by the output signal GOUT[4] of the last stage.
Accordingly, in the forward shift operation, the dummy stage 1 is reset by a control signal, or the output of the inverter of the last stage instead of the scan start signal STV, to thereby prevent the output signal of the dummy stage 1 from remaining during the display blanking period.
FIGS. 34, 35, 36 and 37 are block diagrams respectively showing a bi-directional shift register according to still another exemplary embodiment of the present invention. A dummy stage 0 and a dummy stage 1 are reset by the output signals of the dummy stage 0 and the dummy stage 1 instead of the scan start signal STV in order to prevent the output signals of the dummy stage 0 and the dummy stage 1 from existing during the display blanking period. FIG. 34 shows the connection between the dummy stage 0 and the first stage of FIG. 19, and FIG. 35 shows the connection between the dummy stage 0 and the first stage of FIG. 26. FIG. 36 shows the connection between the dummy stage 1 and the last stage of FIG. 20, and FIG. 37 shows the connection between the dummy stage 1 and the last stage of FIG. 27.
Referring to FIG. 34 and FIG. 35, an output signal of the dummy stage 0 is connected to a hold transistor M5 of the dummy stage 0 through a transistor M13 of the dummy stage 0, and the output signal GOUT[1] of the first stage is connected to a gate of a buffer transistor M3 of the dummy stage 0.
In the dummy stage 0, the forward shift operation occurs when Vbuf=Von, Vdis=Voff. The dummy stage 0 is set (or activated) by the scan start signal STV inputted through the transistor M12 of the dummy stage 0, and is reset (or inactivated) by the output signal GOUT[1] of the first stage. The backward shift operation occurs when Vbuf=Voff, Vdis=Von. The dummy stage 0 is set (or activated) by the output signal GOUT[1] of the first stage, and is reset (or inactivated) by the output signal of the dummy stage 0.
Accordingly, in the backward shift operation, the dummy stage 0 is reset by the output signal of the dummy stage 0, to thereby prevent the output signal of the dummy stage 0 from remaining during the display blanking period.
Referring to FIG. 36 and FIG. 37, an output signal of the dummy stage 1 is connected to a hold transistor M5 of the dummy stage 1 through a transistor M15 of the dummy stage 1, and the output signal GOUT[4] of the last stage is connected to a gate of a buffer transistor M3 of the dummy stage 1.
In the dummy stage 1, the forward shift operation occurs when Vbuf=Von, Vdis=Voff. The dummy stage 1 is set (or activated) by the output signal GOUT[4] of the last stage, and is reset (or inactivated) by the output of the inverter (M6 and M7) of the last stage. The backward shift operation occurs when Vbuf=Voff, Vdis=Von. The dummy stage 1 is set (or activated) by the scan start signal STV inputted through transistor M14 of the dummy stage 1, and is reset (or inactivated) by the output signal GOUT[4] of the last stage.
Accordingly, in the forward shift operation, the dummy stage 1 is reset by a control signal, or the output of the inverter of the last stage instead of the scan start signal STV, to thereby prevent the output signal of the dummy stage 1 from remaining during the display blanking period.
Although the above embodiments discuss the shift register for driving the gate lines of the liquid crystal display device, the present invention may also be utilized in the organic electroluminescent display device.
While the exemplary embodiments of the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the scope of the invention as defined by appended claims.

## Claims

1. A method of driving a plurality of scan lines by providing a display panel with a plurality of scan line driving signals from a gate driver including a shift register, the method comprising:
receiving a scan start signal to generate a first scan line driving signal and lowering a voltage level of the first scan line driving signal so as to inactivate a first scan line in response to a second scan line driving signal;
receiving one of previous scan line driving signals to generate an Nth scan line driving signal for activating an Nth scan line, N being a natural number in a range from two to a number of scan lines except for a last scan line;
lowering a voltage level of the Nth scan line driving signal so as to inactivate the Nth scan line in response to one of next scan line driving signals;
generating a last scan line driving signal from a last stage in response to one of previous scan line driving signals of the last scan line driving signal;
generating a dummy output signal from a dummy stage in response to the last scan line driving signal;
lowering a voltage level of the last scan line driving signal so as to inactivate the last scan line in response to the dummy output signal; and
directly applying the scan start signal to the dummy stage to lower a fourth voltage level of the dummy output signal in response to the scan start signal.

2. A method of driving a plurality of scan lines by providing a display panel with a plurality of scan line driving signals from a gate driver including a shift register, the method comprising:
receiving a scan start signal to generate a first scan line driving signal and lowering a voltage level of the first scan line driving signal so as to inactivate a first scan line in response to a second scan line driving signal;
receiving one of previous scan line driving signals to generate an Nth scan line driving signal for activating an Nth scan line, N being a natural number in a range from two to a number of scan lines except for a last scan line;
lowering a voltage level of the Nth scan line driving signal so as to inactivate the Nth scan line in response to one of next scan line driving signals;
generating a last scan line driving signal form a last stage in response to one of previous scan line driving signals of the last scan line driving signal;
generating a dummy output signal from a dummy stage in response to the last scan line driving signal of a last scan stage;
lowering a voltage level of the last scan line driving signal in response to the dummy output signal so as to inactivate the last scan line;
wherein the last scan stage generates a signal in response to the dummy output signal and the dummy stage is inactivated by lowering a voltage level of the dummy output signal in response to the signal directly applied to the dummy stage from the last scan stage.

3. A method of driving a plurality of scan lines by providing a display panel with a plurality of scan line driving signals from at least one gate driver including at least one shift register including a plurality of stages,
wherein the gate driver provides the scan line driving signals to the scan lines, respectively in a forward shift from a first scan line to a last scan line or in a backward shift from the last scan line to the first scan line, the method comprising:
performing the forward shift to generate a scan line driving signal in a Nth scan stage when a first selection signal, which is transmitted to each of the plurality of stages, has a first voltage level and a second selection signal, which is transmitted to each of the plurality of stages, has a second voltage level, N being a natural number in a range from one to a number of scan lines which are connected to the stages; and
performing the backward shift to generate the scan line driving signal in the Nth scan stage when the first selection signal has a third voltage level and the second selection signal has a fourth voltage level,
wherein the first voltage level is different from the second voltage level and the third voltage level is different from the fourth voltage level.

4. A method of driving a plurality of scan lines by providing a display panel with a plurality of scan line driving signals from a gate driver including a shift register, the scan lines being sequentially selected in a forward shift from a first scan line to a last scan line or in a backward shift from the last scan line to the first scan line, the method comprising:
generating a first scan line driving signal in response to a scan start signal and lowering a first voltage level of the first scan line driving signal in response to a second scan line driving signal so as to perform the forward shift when a first selection signal has a first level, and generating the first scan line driving signal in response to the second scan line driving signal and lowering the first voltage level of the first scan line driving signal in response to a second dummy output signal so as to perform the backward shift when a second selection signal has the first level;
generating 2nd, 3rd, . . . , and (N−1)th scan line driving signals in response to a previous scan line driving signal and lowering a second voltage level of each of the 2nd, 3rd, . . . , and (N−1)th scan line driving signals in response to a one of next scan line driving signals so as to perform the forward shift when the first selection signal has the first level, and generating the 2nd, 3rd, . . . , and (N−1)th first scan line driving signals in response to the one of the next scan line driving signals and lowering the second voltage level of each of the 2nd, 3rd, . . . , and (N−1)th scan line driving signals in response to the previous scan line driving signal so as to perform the backward shift when the second selection signal has the first level, N being a natural number in range from 5 to a number of the scan lines;
generating a Nth scan line driving signal in response to a (N−1)th scan line driving signal and lowering a third voltage level of the Nth scan line driving signal in response to the first dummy output signal so as to perform the forward shift when the first selection signal has the first level, and generating the Nth scan line driving signal in response to the scan start signal and lowering the third voltage level of the Nth scan line driving signal in response to the (N−1)th scan line driving signal so as to perform the backward shift when the second selection signal has the first level;
generating the first dummy output signal in response to the Nth scan line driving signal and lowering the third voltage level of the Nth scan line driving signal in response to the first dummy output signal during the forward shift;
lowering a fourth voltage level of the first dummy output signal;
generating the second dummy output signal in response to the first scan line driving signal and lowering the first voltage level of the first scan line driving signal in response to the second dummy output signal during the backward shift; and

lowering a fifth voltage level of the second dummy output signal.

5. The method of claim 3, further comprising:
generating a first dummy output signal from a first dummy stage during the forward shift; and
applying the first dummy output signal to a last stage of the stages to lower an output level of a last scan line driving signal.

6. The method of claim 5, further comprising:
applying a start scan signal to the first dummy stage to lower an output level of the first dummy output signal during the forward shift.

7. The method of claim 3, further comprising:
generating a second dummy output signal from a second dummy stage during the backward shift; and
applying the second dummy output signal to a first stage of the stages to lower an output level of a first line driving signal.

8. The method of claim 7, further comprising:
applying a start scan signal to the second dummy stage to lower an output level of the second dummy output signal during the backward shift.

9. The method of claim 3, wherein the first voltage level is higher than the second voltage level.

10. The method of claim 3, wherein the fourth voltage level is higher than the third voltage level.

11. The method of claim 10, wherein the fourth voltage level is same as the first voltage level, and the second voltage level is the same as the third voltage level.

12. A display device comprising:
at least one data line:
gate lines insulated from the data line;
at least one pixel comprising at least one first switching element connected to the data line and one of the gate lines;
at least one data driver circuit configured to provide the data image signal to the date line; and
at least one gate driver circuit comprising at least one shift register including a plurality of stages, one of the stages being connected to the one of the gate lines,
wherein the one of the stages is configured to provide the one of the gate lines with a gate driving signal in a forward shift when a level of a first selection signal applied to each of the plurality of stages is higher than a level of a second selection signal applied to each of the plurality of stages during the forward shift, and
wherein the one of the stages is configured to provide the one of the gate lines with a gate driving signal in a backward shift when the second selection signal is higher than the first selection signal during the backward shift.

13. The display device of the claim 12,
wherein the first selection signal transmitted to each of the plurality of stages through a first selection signal line and the second selection signal transmitted to each of the plurality of stages through a second selection signal line.

14. The display device of the claim 13, the shift register further comprising:
a first and a second dummy stages, wherein the plurality of stages are disposed between the first and the second dummy stages.

15. The display device of the claim 14,
wherein the first dummy stage is configured to turn off a pull-up part of a stage electrically connected to the first dummy stage in the forward shift, and the second dummy stage is configured to turn off a pull-up part of a stage electrically connected to the second dummy stage in the backward shift.

16. The display device of the claim 15,
wherein each of the first and second dummy stages comprises a dummy pull-up part configured to output a dummy gate driving signal corresponding to a clock signal applied to the dummy pull-up part, and the dummy pull-up part of the first dummy stage is configured to be turned off in response to a start scan signal in the forward shift, and the dummy pull-up part of the second dummy stage is configured to be turned off in response to the start scan signal in the backward shift.

17. The display device of the claim 15,
wherein each of the first and second dummy stages comprises a dummy pull-up part configured to output a dummy gate driving signal corresponding to a clock signal applied to the dummy pull-up part, and the dummy pull-up part of the first dummy stage is configured to be turned off in response to a start scan signal in the backward shift, and the dummy pull-up part of the second dummy stage is configured to be turned off in response to the start scan signal in the forward shift.

18. The display device of the claim 14,
wherein each of the first and second dummy stages comprises a dummy pull-up part configured to output a dummy gate driving signal corresponding to a clock signal applied to the dummy pull-up part, and a pull-up driver part comprises a second switching element for providing the dummy pull-up part with a first power voltage in response to a start scan signal, and a third switching element for providing the dummy pull-up part with a second power voltage in response to a signal from one of the stages.

19. The display device of the claim 18,
wherein the first power voltage is a negative direct constant voltage, and the second power voltage is a positive direct constant voltage.

20. The display device of the claim 14,
wherein the second dummy stage comprises a first dummy pull-up part configured to output a first dummy gate driving signal corresponding to a clock signal which is applied to the second dummy stage, a fourth switching element for providing the first dummy pull-up part with a second selection signal of the selection signal in response to an output of a pull-up part of one of next stages, and a fifth switching element for providing the first dummy pull-up part with a first selection signal of the selection signal in response to a start scan signal through a sixth switching element or an output of a pull-down driver part of the one of the next stages through a seventh switching element, wherein the sixth switching element is configured to be controlled by the first selection signal and the seventh switching element is configured to be controlled by the second selection signal, and wherein the pull-down driver part of the one of the next stages includes eighth and ninth switching elements, the eighth switching element has a drain and a gate commonly connected with each other to be connected to a second power voltage, a source connected to an output terminal of the pull-down diver part of the one of the next stages, and the ninth switching element has a drain connected to the output terminal of the pull-down driver part of the one of the next stages, a gate connected to an control terminal of the pull-up part of the one of the next stages and a source connected to a first power voltage, and the pull-up part of the one of the next stages is configured to output a gate driving signal corresponding to a clock signal which is applied to the one of the next stages.

21. The display device of the claim 14,
wherein the second dummy stage comprises a first dummy pull-up part configured to output a first dummy gate driving signal corresponding to a clock signal which is applied to the second dummy stage, a fourth switching element configured to provide the first dummy pull-up part with a second selection signal of the selection signal in response to an output of a pull-up part of an one of next stages, and a fifth switching element configured to provide the first dummy pull-up part with a first selection signal of the selection signal in response to a start scan signal through a sixth switching element or the first dummy gate driving signal through a seventh switching element, wherein the sixth switching element is configured to be controlled by the first selection signal and the seventh switching element is configured to be controlled by the second selection signal, and wherein the pull-up part of the one of the next stages is configured to output a gate driving signal corresponding to a clock signal which is applied to the one of the next stages.

22. The display device of the claim 14,
wherein the first dummy stage comprises a second dummy pull-up part configured to output a second dummy gate driving signal corresponding to a clock signal which is applied to the first dummy stage, a tenth switching element configured to provide the second dummy pull-up part with a first selection signal of the selection signal in response to an output of a pull-up part of an one of previous stages, and an eleventh switching element configured to provide the second dummy pull-up part with a second selection signal of the selection signal in response to a start scan signal through a twelfth switching element or an output of a pull-down driver part of the one of the previous stages through a thirteenth switching element, wherein the twelfth switching element is configured to be controlled by the second selection signal and the thirteenth switching element is configured to be controlled by the first selection signal, and wherein the pull-down driver part of the one of the previous stages includes fifteenth and sixteenth switching elements, the fifteenth switching has a drain and a gate commonly connected with each other to be connected to a second power voltage, a source connected to an output terminal of the pull-down diver part of the one of the previous stages, and the sixteenth switching element has a drain connected to the output terminal of the pull-down driver part of the one of the previous stages, a gate connected to a control terminal of the pull-up part of the one of the previous stages and a source connected to a first power voltage, and the pull-up part of the one of the previous stages is configured to output a gate driving signal corresponding to a clock signal which is applied to the one of the previous stages.

23. The display device of the claim 14,
wherein the first dummy stage comprises a second dummy pull-up part configured to output a second dummy gate driving signal corresponding to a clock signal which is applied to the first dummy stage, a tenth switching element configured to provide the second dummy pull-up part with a first selection signal of the selection signal in response to an output of a pull-up part of an one of previous stages, and a eleventh switching element configured to provide the second dummy pull-up part with a second selection signal of the selection signal in response to a start scan signal through a twelfth switching element or the second dummy gate driving signal through a thirteenth switching element, wherein the twelfth switching element is configured to be controlled by the second selection signal and the thirteenth switching element is configured to be controlled by the first selection signal, and wherein the pull-up part of the one of the previous stages is configured to output a gate driving signal corresponding to a clock signal which is applied to the one of the previous stages.

24. The display device of the claim 12, wherein the one of the stages comprising:
a first pull-up part configured to provide the one of the gate lines with the gate driving signal corresponding to a clock signal which is applied to the first pull-up part; and
a first pull-up driver part configured to turn on the first pull-up part in response to a signal from one of previous stages of the stages or a scan start signal in the forward shift, configured to turn off the first pull-up part in response to a signal from one of next stages of the stages or a signal from a first dummy stage in the forward shift, configured to turn off the first pull-up part in response to the signal from the one of the previous stages of the stages or a signal from a second dummy stage in the backward shift, and configured to turn on the first pull-up part in response to the one of the next stages of the stages or the scan start signal in the backward shift.

25. The display device of the claim 24,
wherein the first pull-up driver part comprises a seventeenth switching element which is configured to provide the first pull-up part with a first selection signal of the selection signal in response to the one of the previous stages, and the first pull-up driver part further comprises a eighteenth switching element which is configured to provide the first pull-up part with a second selection signal of the selection signal in response to the one of the next stages.

26. The display device of the claim 24, the first pull-up driver part comprising:
a nineteenth switching element configured to provide the first pull-up part with a first selection signal of the selection signal in response to the start scan signal through a twentieth switching element or the signal from the second dummy stage adjacent to the stage through a twenty-first switching element; and
a twenty-second switching element configured to provide the first pull-up part with a second selection signal of the selection signal in response to one of next stages, wherein the twentieth switching element is controlled by the first selection signal and the twenty-first switching element is controlled by the second selection signal.

27. The display device of the claim 24, the first pull-up driver part comprising:
a twenty-second switching element configured to provide the first pull-up part with a first selection signal of the selection signal in response to one of previous stages; and
a twenty-third switching element configured to provide the first pull-up part with a second selection signal of the selection signal in response to a start scan signal through a twenty-fourth switching element or a first dummy stage adjacent to the stage through a twenty-fifth switching element, wherein the twenty-fourth switching element is controlled by the second selection signal and the twenty-fifth switching element is controlled by the first selection signal.

28. The display device of the claim 24, the first pull-up driver part comprising:
a twenty-sixth switching element configured to provide the first pull-up part with a second power voltage in response to one of previous stages through a twenty-seventh switching element or one of next stages through a twenty-eighth switching element, and
a twenty-ninth switching element configured to provide the first pull-up part with a first power voltage in response to the one of the previous stages through a thirtieth switching element or the one of the next stages through a thirty-first switching element,
wherein the twenty-seventh switching element is controlled by a first selection signal of the selection signal of the selection signal, the twenty-eighth is controlled by a second selection signal of the selection signal, the thirtieth switching element is controlled by the second selection signal of the selection signal, and a thirty-first switching element is controlled by the first selection signal.

29. The display device of the claim 24, the first pull-up driver part comprising:
a thirty-second switching element configured to provide the first pull-up part with a second power voltage in response to a start scan signal through a thirty-third switching element or one of next stages through a thirty-fourth switching element; and
a thirty-fifth switching element configured to provide the first pull-up part with a first power voltage in response to one of the next stages through a thirty-sixth switching element or a second dummy stage adjacent to the stage through a thirty-seventh switching element,
wherein the thirty-third switching element is controlled by a first selection signal of the selection signal, the thirty-fourth switching element is controlled by a second selection signal of the selection signal, the thirty-sixth switching element is controlled by the first selection signal, and a thirty-seventh switching element is controlled by the second selection signal.

30. The display device of the claim 24, the first pull-up driver part comprising:
a thirty-eighth switching element configured to provide the first pull-up part with a second power voltage in response to a start scan signal through a thirty-ninth switching element or one of previous stages through a fortieth switching element; and

a forty-first switching element configured to provide the first pull-up part with a first power voltage in response to the one of the previous stages through a forty-second switching element or a first dummy stage adjacent to the stage through a forty-third switching element, wherein the thirty-ninth switching element is controlled by a second selection signal of the selection signal, the fortieth switching element is controlled by a first selection signal of the selection signal, the forty-second switching element is controlled by the second selection signal, and a forty-third switching element is controlled by the first selection signal.

31. The display device of the claim 12,
wherein the one of the stages comprises a plurality of switching elements which are simultaneously formed with the first switching elements.

32. The display device of the claim 13,
wherein each of the stages receives one of a first clock signal from a first clock signal line and a second clock signal from a second clock signal line, phases of the first clock signal and the second signal in the forward shift are different from phases of the first clock signal and the second clock signal in the backward shift, respectively.

33. The display device of the claim 31,
wherein the phase of the first clock signal in the forward shift is same as the phase of the second clock signal in the backward shift.