This application claims priority to and the benefit of Korean Patent Application No. 10-2011-0096179 filed in the Korean Intellectual Property Office on Sep. 23, 2011, the entire contents of which are incorporated herein by reference.
(a) Field of the Invention
The present invention relates to a shift register and a gate driving circuit of a display device using the same, and more particularly, to a shift register, which can adjust a scan direction when a screen of a display device is upside down, and a gate driving circuit of the display device using the same.
(b) Description of the Related Art
Occasionally, a display device that has recently been used in a portable terminal may display images on a screen as it is reversed up and down or left and right in accordance with a user's intention. For these cases, a gate driving circuits of the display device need to be designed to change a scan direction.
A conventional shift register includes a plurality of thin film transistors (TFT) as disclosed in Korean Patent No. 10-1020627.
Referring to
In the conventional shift register, the inverter unit 20 is basically consisted of a TFT T5 and a TFT T9. The TFT T5 constantly keeps turned on by a bias voltage Vbias, and the TFT T9 is biased by voltage difference between VGL and LVGL since voltage applied to a source of the TFT T9 is a voltage of LVGL. Thus, even if the TFT T9 is turned on, an X node cannot be entirely dropped into the voltage of LVGL. Further, even when the TFT T9 is turned off, the X node cannot be increased up to the bias voltage Vbias. Therefore, the X node cannot be fully inverted.
To compensate for insufficient driving performance for the TFTs and secure reliability, a conventional inverter further need to include two TFTs T6 and T8 in addition to the TFTs T5 and T9. Thus, the conventional inverter includes all four of TFTs, and adds an LVGL signal to improve the reliability. Like this, such a conventional shift register needs a plurality of thin film transistors and signal lines to improve the off-characteristics. This causes problems of enlarging a dead space of a display device, resulting in the display having bigger size than originally planned and modifying a structure of the gate driving circuit.
Further, a shift register of a recent gate driving circuit has an additional function to change the order of applying signals to gate lines depending on rotation of a display screen. To this end, as shown in
Korean Patent No. 10-1020627 (Mar. 2, 2011)
Korean Patent Publication No. 10-2007-0037793 (Apr. 9, 2007)
Korean Patent No. 10-0698239 (Mar. 15, 2007)
Japanese Patent No. 4391107 (Oct. 16, 2009)
Accordingly, the present invention is conceived to solve the forgoing problems, and an aspect of the present invention is to provide a shift register and a gate driving circuit that show excellent operation reliability with elements less than those of the conventional structure.
Another aspect is to provide a shift register and a gate driving circuit using the same having an improved input unit as compared with that of the conventional structure and enabling a bidirectional scan.
The foregoing and other aspects of the invention may be achieved by a shift register and a gate driving circuit using the same according to an exemplary embodiment.
According to an exemplary embodiment, there is provided a gate driving circuit comprising a plurality of shift registers sequentially connected to each other and respectively supplied scan signals to a plurality of gate lines of a display device, each shift register including: an input unit which outputs a forward or backward input signal as a direction control signal to a first node by an output signal from a previous or subsequent shift register of the shift register; an inverter unit which connects with the first node, generates an inverting signal for a signal of the first node and outputs the inverting signal to a second node; an output unit which includes a pull-up unit connecting to the first node, for activating a first clock signal by the signal of the first node and outputting the first clock signal as an output signal to corresponding gate line, and a pull-down unit for activating and outputting a pull-down output signal by a signal of the second node; and a reset unit which periodically resets the first node by a second clock signal, wherein the inverter unit is controlled by the second clock signal.
According to another exemplary embodiment, there is provided a shift register including a first switching device which includes a gate terminal connected to an output terminal of a previous shift register ((generally an (N−1)th or (N−2)th shift register), a drain terminal to receive a forward or backward input signal, and a source terminal connected to a first node; a second switching device which includes a gate terminal connected to an output terminal of a subsequent shift register((generally an (N+1)th or (N+2)th shift register), a drain terminal to receive a forward or backward input signal, and a source terminal connected to a first node; a third switching device which includes a gate terminal connected to the first node, a drain terminal to receive a first clock signal, and a source terminal connected to the first node and corresponding gate line(generally a Nth shift register); a fourth switching device which includes a gate terminal connected to a second node, a drain terminal connected to the first node, and a source terminal connected to a low level voltage terminal; a fifth switching device which includes a gate terminal connected to the gate terminal of the third switching device and the second node, a drain terminal connected to the first node, and a source terminal connected to the low level voltage terminal; a sixth switching device which includes a gate terminal to receive a second clock signal, a drain terminal to receive a bias voltage, and a source terminal connected to the second node; a seventh switching device which includes a gate terminal connected to the first node, a drain terminal connected to the second node and the source terminal of the sixth switching device, and a source terminal connected to the low level voltage terminal; and an eighth switching device which includes a gate terminal to receive the second clock signal, a drain connected to the first node, and a source terminal connected to the low level voltage terminal.
According to still another exemplary embodiment, there is provided a gate driving circuit comprising a plurality of shift registers sequentially connected and respectively supplying scan signals to a plurality of gate lines of a display device, each shift register including: an input unit which receives an output signal from a previous shift register of the shift register, and outputs the output signal to a first node; an inverter unit which connects with the first node, generates an inverting signal for a signal of the first node, and outputs the inverting signal to a second node; an output unit which includes a pull-up unit for activating a first clock signal by the signal of the first node and outputting the first clock signal as an output signal to the corresponding gate line, and a pull-down unit for activating and outputting a pull-down output signal to the corresponding gate line by a signal of the second node; and a reset unit which periodically resets the first node by a second clock signal.
The inverter unit and the reset unit may be controlled by the second clock signal.
Also, a input signal to an input unit of the first or last shift register among the plurality of shift registers is a pulse type input start signal (STV).
According to still another exemplary embodiment, there is provided a shift register including a first switching device which includes a gate terminal and drain terminal connected in common to an output terminal of a previous shift register, and a source terminal connected to a first node; a second switching device which includes a gate terminal connected to the first node, a drain terminal to receive a first clock signal, and a source terminal connected to the first node; a third switching device which includes a gate terminal connected to a second node, a drain terminal connected to the first node, and a source terminal connected to a low level voltage terminal; a fourth switching device which includes a gate terminal connected to the gate terminal of the third switching device and the second node, a drain terminal connected to the first node, and a source terminal connected to the low level voltage terminal; a fifth switching device which includes a gate terminal to receive a second clock signal, a drain terminal to receive a high level voltage, and a source terminal connected to the second node; a sixth switching device which includes a gate terminal connected to the first node, a drain terminal connected to the second node and the source terminal of the fifth switching device, and a source terminal connected to the low level voltage terminal; and a seventh switching device which includes a gate terminal to receive the second clock signal, a drain terminal connected to the first node, and a source terminal connected to the low level voltage terminal.
The above and/or other aspects of the present invention will become apparent and more readily appreciated from the following description of the exemplary embodiments, taken in conjunction with the accompanying drawings, in which:
A display driving circuit, in which a gate driving circuit including a plurality of shifter registers for shifting and outputting an input signal is embedded on a display panel.
The display panel is divided into a display region and a non-display region. Specifically, the shift register is formed on the non-display region.
Further, when gate driving circuits employing the shift registers of the invention are disposed on both side of the display panel and respectively drive odd-numbered gate lines and even numbered gate lines, this is called a dual type arrangement of gate driving circuit. On the other hand, when one or more gate driving circuits are disposed on one-side of the display panel and drive the gate lines, this is called a single type arrangement of gate driving circuit.
Hereinafter, a shift register according to an exemplary embodiment of the invention will be described with reference to the accompanying drawings.
If one gate driving circuit in left can drives the odd-numbered gate lines in order of 1, 3, 5. . . , the other gate driving circuit in right can drives the even-numbered gate lines in order of 2, 4, 6. . . .
As shown in
Referring to
The shift register in this exemplary embodiment of the invention performs bidirectional driving, i.e., the shift register can perform forward and reverse direction scans. The shift register includes an input unit 60, an inverter unit 20, a reset unit 30 and an output unit 40.
The input unit 60 receives a forward input signal FW having a gate high voltage VGH or a backward input signal BW having a gate low voltage VGL based on an output signal of a previous or subsequent shift register. The input unit 60 transmits an output signal to a P node (also called a ‘bootstrap node’) connecting with an output terminal N Gout. As compared with the conventional structure of
In the case of the dual type where the gate driving circuits are arranged in left and right opposite sides of the display panel and respectively drive the odd-numbered gate lines and the even-numbered gate lines, the output signal of the anterior shift register is an (N−2)th output signal N−2 Gout in the nth gate driving circuit by way of example. On the other hand, if the output signal of the posterior shift register is an (N+2)th output signal N+2 Gout in the nth gate driving circuit by way of example. In contrast to the dual type, in the case of the single type where the gate driving circuit is arranged in only one side of the display panel, the output signal of the anterior shift register is an (N−1)th output signal N−1 Gout in the nth gate driving circuit by way of example. On the other hand, if the output signal of the posterior shift register is an (N+1)th output signal N+1 Gout in the nth gate driving circuit by way of example.
The input unit 60 includes TFTs T1 and T10. The TFT T1 has a gate terminal connected to an output terminal of the previous shift register, a drain terminal receiving a directional input signal (e.g., a forward input signal FW in the case of the forward driving), and a source terminal connected to the P node. The TFT T10 has a gate terminal connected to an output terminal of the subsequent shift register, a drain terminal receiving a directional input signal (e.g., a backward input signal BW in the case of the forward driving), and a source terminal connected to the P node.
Thus, the input unit 60 changes the signal applied to the drain terminal of each transistor T1 or T10 into the forward input signal FW or the backward input signal BW in accordance with the scan direction.
The inverter unit 20 is connected to the P node. The inverter unit 20 is driven by the second clock signals CLK2 or CLK4 to generate an inverting signal for the signal of the P node and output it to an X node.
The inverter unit 20 includes TFTs T5 and T9. The TFT T5 has a gate terminal receiving the second clock signals CLK2 or CLK4, a drain terminal receiving a high level voltage as Vbias (a bias voltage), and a source terminal connected to the X node and a drain terminal of the TFT T9. The TFT 9 has a gate terminal connected to the P node, the drain terminal connected to the X node and the source terminal of the TFT T5, and a source terminal connected to a low level voltage terminal having a low level voltage as VGL.
To improve the off-characteristics, the conventional inverter unit uses four TFTs and needs a LVGL signal in addition to the VGL signal. However, the inverter unit 20 in the present exemplary embodiment of the invention controls the TFT T5 to be driven by the clock signal, and therefore two TFTs are enough to achieve desired characteristics without the LVGL signal. Accordingly, the inverter unit 20 in this exemplary embodiment of the invention is very useful as compared with the conventional one.
The reset unit 30 periodically resets the P node with the second clock signals CLK2 or CLK4.
The reset unit 30 includes a TFT 7. The TFT 7 has a gate terminal receiving the second clock signals CLK2 or CLK4, a drain terminal connected to the P node, and a source terminal connected to the low level voltage as VGL.
The output unit 40 is connected to the P node, the X node and corresponding gate line. The output unit 40 includes a pull-up unit for outputting a signal of the P node as a pull-up output signal in sync with the first clock signals CLK1 or CLK3 to corresponding gate line, and a pull-down unit for outputting a pull-down output signal based on a signal of the X node to corresponding gate line.
The pull-up unit includes a TFT T3. The TFT T3 has a gate terminal connected to the P node, a drain terminal receiving the first clock signals CLK1 or CLK3, and a source terminal connected to the output terminal N Gout connecting with the P node.
The pull-down unit includes TFTs T2 and T4. The TFT T2 has a gate terminal connected to the X node, a drain terminal connected to the P node, and a source terminal connected to the low level voltage terminal VGL. The TFT T4 has a gate terminal connected to both the gate of the TFT T2 and the X node, a drain terminal connected to the output terminal N Gout, and a source terminal connected to the low level voltage terminal VGL. Meanwhile, the TFTs T2 and T4 may also be called a stabilization device for continuously maintaining the voltage levels of the P node and the output terminal N Gout as the level of the low level voltage VGL after outputting a pull-up output signal to corresponding gate line.
A capacitor C1 is provided for boosting and stabilizes the off-level characteristics of the output signal from the output terminal N Gout. The capacitor C1 is connected between the gate and source of the TFT T3.
In
Thus, each clock signal is supplied to a high level once per 4 H period, so that the voltage level of the X node can increase through the TFT T5 once per 4 H period. Thus, the X node can keep a high level higher than the conventional high level for time of one frame. This means that the X node can keep a high voltage more exactly than that of the conventional case. Also, the P node is reset through the TFT T7 once per 4 H period, and it is thus advantageous to stabilize the shift register.
With this configuration, the shift register according to an exemplary embodiment of the invention operates as follows.
In the case of a forward driving, the output signal from the (N−2)th shift register is applied to the gate of the TFT T1 of the input unit 60, and the forward input signal FW is applied to the drain of the TFT T1. After that, the output signal from the (N+2)th shift register is applied to the gate of the TFT T10 of the input unit 60, and the backward input signal BW is applied to the drain of the TFT T10.
A backward driving is a contrast to the forward driving. That is, the output signal from the (N+2)th shift register is applied to the gate of the TFT T10 of the input unit 60, and the forward input signal FW is applied to the drain of the TFT T10. After that, the output signal from the (N−2)th shift register is applied to the gate of the TFT T1 of the input unit 60, and the backward input signal BW is applied to the drain of the TFT T1.
Accordingly, in the case of the forward driving, the TFT T1 operates as an input TFT, and the TFT T10 operates as an additional reset TFT separately from the TFT T7. In the case of the backward driving, the TFT T10 operates as the input TFT, and the TFT T1 operates as the reset TFT. Thus, the P node has a voltage level of VGH-a obtained by subtracting a threshold voltage of the TFT T1 or T10 from VGH. The capacitor C1 is charged. The TFT T9 becomes turned on and the X node has a voltage level of VGL. The TFTs T2 and T4 become turned off since the X node has a low level. In this state, the P node maintains a floating state while keeping the voltage level. Therefore, the TFT T3 is turned on and maintains the same state for the same time as the P node, thereby outputting the clock signals CLK1 or CLK3 as the output signal of N Gout to corresponding gate line.
Then, the clock signal CLK2 or CLK4 having a high level is applied to the TFTs T7 and T5, and thus the TFTs T7 and T5 are turned on. As the TFT T5 is turned on, the X node becomes a high level voltage Vbias. As the TFT T7 is turned on, the P node is dropped into a level of VGL.
If the X node has the high level voltage, the TFTs T2 and T4 are turned on and the P node and the output signal of N Gout maintain the low level voltage.
The foregoing operations of the shift register according to the present exemplary embodiment will be described in more detail with reference to the timing diagrams of
In the case of the single type, as shown in
The odd-numbered shift register uses the clock signals CLK1 and CLK3 as the output signals and the clock signals CLK2 and CLK4 for the reset, and the even-numbered shift register uses the clock signals CLK2 and CLK4 as the output signals and the clock signals CLK3 and CLK1 for the reset. Thus, the single type uses four clock signals for the bidirectional driving.
In the forward driving as shown in
In the backward driving as shown in
In the case of the dual type, as shown in
To prevent the input timing and the reset timing from overlapping each other, each of the shift registers formed on the opposite sides of the display panel has to use four clock signals different in a period of 1 H or more. For example, in the case of the dual type, each of the shift registers provided on the opposite sides of the display panel needs four clock signals because the order of clocks has an effect on the forward or backward driving.
In
In
Referring to
The shift register according to this exemplary embodiment does not include the input unit for bidirectional input provided in the shift register of
For the unidirectional driving, the input unit 10 receives an output signal from a previous shift register (generally the (N−2)th output N−2 Gout is a output signal that applied to the (N−2)th gate line) or a start signal STV (input) as a input signal, and transmits it to the P node (also called a ‘bootstrap node).
The input unit 10 includes a TFT T1. The TFT T1 has a gate terminal and a drain terminal connected in common to the output terminal of the previous shift register. The TFT T1 has a source terminal connected to the P node.
The inverter unit 20, the reset unit 30 and the output unit 40 of
With this configuration, the shift register according to this exemplary embodiment operates as follows. Hereinafter, the following descriptions are achieved on the assumption that the shift register of
A pulse type input start signal STV (input) or an output signal N−2 Gout of a previous (e.g., (n−2)th) shift register (not shown) is input through a gate terminal of the TFT T1. Then, the TFT T1 becomes turned on, and the P node has a positive level. In this case, the P node has a voltage level of VGH-a obtained by subtracting the threshold voltage of the TFT T1 from VGH.
Meanwhile, the X node is dropped into a voltage level of VGL by the TFT T9 turned on as the voltage of the P node increases. Also, the output signal N Gout maintains a low level since the TFT T3 is turned on as the voltage of the P node increases but the clock signal maintains VGL. While receiving the input through the TFT T1, the capacitor C1 is charged.
Then, the input signal (e.g., N−2 Gout) becomes a signal having the low level VGL, and the TFT T1 becomes turned off. In this case, the P node enters a floating state, and maintains the floating state until receiving a reset signal. Accordingly, the TFT T3 is turned on by the high level voltage of the P node, and keeps the same state for the same time as the P node. When the clock signal CLK1 or CLK3 is applied, the P node is bootstrapped, and the TFT T3 outputs the clock signal at the same time.
After the clock signal CLK1 or CLK3, if the clock signal CLK2 or CLK4 is applied to the TFTs T7 and T5, the TFTs T7 and T5 are turned on. As the TFT T5 is turned on, the X node has a high level voltage Vbias. As the TFT T7 is turned on, the P node is dropped into a low level voltage as VGL. Like this, if the X node has the high level voltage Vbias, the TFTs T2 and T4 are turned on, thereby maintaining the P node to have the low level voltage.
In other words, the applied input signal causes the TFT T1 to be turned on and the P node to be precharged. If the clock signal CLK1 or CLK3 is applied to the TFT T3, the P node is bootstrapped so that the clock signal CLK1 or CLK3 can be output to the output terminal N Gout via the TFT T3.
Meanwhile, if the P node is bootstrapped, the TFT T9 is turned on. When the P node is bootstrapped, the clock signal CLK2 or CLK4 has a low level voltage (e.g., VGL). If the clock signal CLK2 or CLK4 has a low level voltage, the TFT T5 maintains an off state. As the TFT T9 is turned on, the X node is dropped into a low level voltage as VGL, and the TFTs T2 and T4 for stabilization or the like are turned off.
If the clock signal CLK2 or CLK4 is applied at a timing after the clock signal CLK1 or CLK3, the TFTs T7 and T5 are turned on. Thus, the P node is reset through the TFT T7, and the voltage level of the X node increases up to a level of Vbias−Vth through the TFT T5. As the voltage level of the X node increases, a gate bias of “the high level voltage of the X node” is applied to the gate terminals of the TFTs T2 and T4, so that the TFTs T2 and T4 are turned on.
Like this, each clock signal is supplied to a high level once per 4 H period, so that the voltage level of the X node can increase through the TFT T5 once per 4 H period. Thus, the X node can keep a high level higher than the conventional high level for time of one frame. This means that the X node can keep a high level voltage more exactly than that of the conventional case. Also, the P node is reset through the TFT T7 once per 4 H period, and it is thus advantageous to stabilize the shift register.
As described above, there is provided a shift register, in which not an output waveform of the next terminal but a clock signal is applied to a reset TFT, thereby reducing a load in an output. Also, a P node is reset at every 4 H, thereby improving off-characteristics.
Further, the clock signal is used for the reset, so that the conventional TFT for the reset can be omitted.
Furthermore, the clock signal is employed for the reset, and thus there is no need of a suicide dummy terminal for resetting the last terminal. Accordingly, the suicide dummy terminal can be removed, so that a panel can be designed with a more space to spare than the conventional panel.
While this invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.
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