KR20140005483A - Display device and driving method the same - Google Patents

Abstract

An embodiment of the present invention provides a display device comprising; a display panel including a sub-pixel formed on a display area; a gate driving part which is formed on a non-display area of the display panel and supplies a gate signal to the sub-pixel; a threshold voltage sensing part formed on the display panel; and a threshold voltage compensating part which supplies a constant current to the threshold voltage sensing part and compensates a threshold voltage of an oxide thin film transistor included at least one of the sub-pixel and the gate driving part based on the change of voltage. The threshold voltage compensating part comprises; a sensing transistor which senses the movement of the threshold voltage in response to the constant current inputted through a current pass; a diode pass transistor which wires drain and gate electrodes of the sensing transistor and forms it as a diode connection state; and a gate control transistor which forms a temperature stress in the sensing transistor.

Description

Display Device and Driving Method the same

An embodiment of the present invention relates to a display apparatus and a driving method thereof.

As the information technology is developed, the market of display devices, which is a connection medium between users and information, is getting larger. Accordingly, the use of display devices such as organic light emitting display (OLED), liquid crystal display (LCD), plasma display panel (PDP), and the like is increasing.

Some of the aforementioned display devices, for example, a liquid crystal display or an organic light emitting display device, include a display panel including subpixels arranged in a matrix and a driving unit for driving the display panel. The driver includes a gate driver for supplying a gate signal (or scan signal) to the display panel and a data driver for supplying a data signal to the display panel.

The subpixels and the gate driver include a thin film transistor and the like. Among the thin film transistors, the oxide thin film transistor (Oxide TFT) has a good advantage over the amorphous silicon thin film transistor (a-Si TFT) in terms of current mobility and off current. Therefore, the oxide thin film transistor can be easily reduced in size, reduced bezel area, and reduced power consumption, which is advantageous for developing a high quality display device.

However, the display device using the oxide thin film transistor causes a Vth shift (threshold voltage moves in a positive or negative direction) of the oxide thin film transistor according to a bias temperature illumination (BTIS) environment. In addition, deterioration of the characteristics of the device is deteriorated, and driving of the display device, display quality degradation, and shortening of the lifespan are caused.

An embodiment of the present invention for solving the above problems of the background technology, to prevent the deterioration of the device by detecting and compensating the threshold voltage shift of the oxide thin film transistor according to the Bias (Bias Temperature Illumination Stress) environment In addition, the present invention provides a display device and a driving method thereof that can improve a driving failure of a display device, prevent a display quality from deteriorating, and improve a lifetime.

Embodiments of the present invention provide a display panel including a subpixel formed in a display area. A gate driver formed in the non-display area of the display panel to supply a gate signal to the subpixel; A threshold voltage detector formed on the display panel; And a threshold voltage compensator for supplying a constant current to the threshold voltage detector and compensating the threshold voltage of the oxide thin film transistor included in at least one of the subpixel and the gate driver based on the change in voltage. Forming a bias temperature stress in the sense transistor for sensing the shift of the threshold voltage in response to a constant current input through the diode, a diode pass transistor connecting the drain electrode and the gate electrode of the sense transistor to a diode connection state A display device including a gate control transistor is provided.

The threshold voltage compensator determines whether the threshold voltage of the sensing transistor is negative or positive based on the change of the sensing voltage formed at the drain electrode of the sensing transistor when the sensing transistor is in the diode connection state, and provides a compensation signal according to the determination result. Can supply

The gate control transistor may turn on and off the gate electrode of the sensing transistor so that the threshold voltage shifting characteristic of the sensing transistor represents the threshold voltage shifting characteristic of the oxide thin film transistor.

The gate control transistor may be turned off and the diode pass transistor may be turned on during the blank period in which the gate signal is not supplied to the display panel.

The threshold voltage detector includes a current input transistor that is turned on so that a constant current is input through the current path, a current output transistor that is turned on to form an output path at a constant current output through the source electrode of the sensing transistor, and a gate supplied to the gate driver. It may include a discharge transistor that is turned on in response to the start signal to discharge the sense voltage of the sense transistor.

The gate control transistor may be turned on in response to the first control signal, and the current input transistor, the diode pass transistor, and the current output transistor may be turned on in response to the second control signal having a pulse opposite to the first control signal.

The threshold voltage compensator may compensate for the driving voltage supplied to the gate driver.

The threshold voltage compensator may compensate for the gate low voltage supplied to the subpixel.

Transistors included in the threshold voltage sensing unit may be formed of an oxide thin film transistor.

In another aspect, an embodiment of the present invention provides a method of driving a display device for compensating a threshold voltage of an oxide thin film transistor included in at least one of a subpixel and a gate driver. Supplying a first control signal in a logic high state to the transistor to form a bias temperature stress on the gate electrode of the sense transistor; Supplying a first signal in a logic low state during a blank period during which a gate signal is not supplied to the display panel to stop forming a bias temperature stress on the gate electrode of the sensing transistor; The second control signal in a logic-high state is supplied to the current input transistor, the diode pass transistor, and the current output transistor during the blank period in which the gate signal is not supplied to the display panel, thereby supplying a constant current through the current path and simultaneously drain electrode of the sensing transistor. Connecting the gate electrode and the gate electrode to form a diode connection state and detecting a shift of the threshold voltage of the sensing transistor; And determining whether the threshold voltage of the sensing transistor is negative or positive based on the change of the sensing voltage formed at the drain electrode of the sensing transistor and supplying a compensation signal according to the determination result. to provide.

The supplying of the compensation signal may include supplying a gate start signal supplied to the gate driver to the discharge transistor so that the sensing voltage of the sensing transistor is discharged.

The supplying of the compensation signal may compensate for one or more of the driving voltage supplied to the gate driver and the gate low voltage supplied to the subpixel using the compensation signal.

According to an embodiment of the present invention, a device capable of detecting and compensating a threshold voltage shift of an oxide thin film transistor according to a bias temperature stress environment is used to prevent deterioration of the device, to improve driving failure of a display device, and to reduce display quality. There is an effect to provide a display device and a driving method thereof that can prevent and improve the life.

1 is a schematic configuration diagram of a display device according to an exemplary embodiment of the present invention.
FIG. 2 is a configuration diagram of the gate driver shown in FIG. 1. FIG.
3 is a diagram illustrating a configuration of a subpixel illustrated in FIG. 1.
4 is a cross-sectional view of an oxide thin film transistor included in a gate driver and a subpixel.
5 is a graph illustrating a threshold voltage shift according to a bias temperature stress of an oxide thin film transistor.
6 is a waveform diagram illustrating a node characteristic according to a threshold voltage shift according to a bias temperature stress of a shift register included in a gate driver.
FIG. 7 is a waveform diagram illustrating degradation of output characteristics of a shift register with time when a bias temperature stress is applied. FIG.
8 is a circuit diagram illustrating a threshold voltage detector and a threshold voltage compensator according to an exemplary embodiment of the present invention.
9 is a drive waveform diagram of the circuit shown in FIG. 8;
FIG. 10 is a diagram illustrating a threshold voltage sensing principle using the sensing transistor illustrated in FIG. 8.
11 is a simulation result diagram of sensing a threshold voltage shift of a sensing transistor.
12 is a view for explaining a concept of threshold voltage compensation according to the change of the characteristics of the oxide thin film transistor.
13 is an exemplary circuit diagram of a shift register to which a threshold voltage detection unit is applied.
14 to 16 illustrate various examples of applying a threshold voltage detector on a display panel.
17 is a flowchart illustrating a method of driving a display device according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a schematic diagram of a display device according to an exemplary embodiment of the present invention, FIG. 2 is a schematic diagram of a gate driver shown in FIG. 1, and FIG. 3 is a schematic diagram of a subpixel illustrated in FIG. 1.

1 to 3, a display device according to an exemplary embodiment includes a display panel 110, gate drivers 120A and 120B, a data driver 130, and a threshold voltage detector 140A and 140B. Threshold voltage compensation unit 150 is included.

The display panel 110 displays an image corresponding to the gate signal supplied from the gate drivers 120A and 120B and the data signal supplied from the data driver 130. The display panel 110 includes a liquid crystal display panel including a liquid crystal cell included in the subpixel SP or an organic light emitting display panel including an organic light emitting diode included in the subpixel SP. The display unit AA of the display panel 110 includes a plurality of subpixels SP. The subpixel SP includes a thin film transistor TFT that operates in response to a gate signal and a data signal supplied through the gate line GL1 and the data line DL1. One or more thin film transistors (TFTs) are included according to the configuration of the display panel 110. The thin film transistor TFT is formed of an oxide thin film transistor TFT.

The gate drivers 120A and 120B generate gate signals in response to the gate driving signals GDC supplied from the outside, and sequentially output the gate signals generated through the gate lines GL. The gate drivers 120A and 120B are composed of a plurality of stages STG1 to STGm. Each stage includes a shift register. The shift register includes a pull-up transistor Tup and a pull-down transistor Tdn. The pull-up transistor Tup outputs a gate signal corresponding to a logic high gate voltage according to the voltage state of the Q node Q-node, and the pull-down transistor Tdn according to the voltage state of the QB node QB-node. A gate signal corresponding to the gate voltage of the logic low is output. The gate drivers 120A and 120B are formed in the non-display area NA of the display panel 110 along with a thin film transistor process of the subpixel SP in a gate in panel manner. Therefore, the transistors Tup and Tdn included in the gate drivers 120A and 120B are also formed of an oxide thin film transistor.

The data driver 130 generates a data signal corresponding to the data driving signal and the data signal supplied from the outside and outputs the generated data signal through the data lines DL. The data driver 130 converts the digital data signal into an analog data signal and outputs the data signal. Unlike the gate drivers 120A and 120B, the data driver 130 is formed on an external substrate connected to the display panel 110 in the form of an integrated circuit (IC).

The threshold voltage detectors 140A and 140B detect whether the thin film transistors have a threshold voltage by using a thin film transistor that represents an oxide thin film transistor included in at least one of the subpixel SP and the gate drivers 120A and 120B. . Threshold voltage sensing units 140A and 140B are formed in the non-display area NA of the display panel 110.

The threshold voltage compensator 150 supplies a constant current to the threshold voltage detectors 140A and 140B and based on the change in the voltage of the thin film transistor included in the threshold voltage detectors 140A and 140B. The threshold voltage of the oxide thin film transistor included in at least one of the gate drivers 120A and 120B is compensated for. The threshold voltage compensation unit 150 may be formed in a separate integrated circuit form or included in the data driver 130 unlike the threshold voltage detection units 140A and 140B.

Hereinafter, the structure of the oxide thin film transistor included in the gate driver and the subpixel, and the characteristic degradation caused by the shift of the threshold voltage of the oxide thin film transistor will be described.

4 is a cross-sectional view of an oxide thin film transistor included in a gate driver and a subpixel, and FIG. 5 is a graph for explaining threshold voltage shift according to a bias temperature stress of an oxide thin film transistor, and FIG. 6 is a shift register included in a gate driver. FIG. 7 is a waveform diagram illustrating a node characteristic according to a threshold voltage shift according to a bias temperature stress. FIG. 7 is a waveform diagram illustrating degradation of an output characteristic of a shift register according to a time when a bias temperature stress is applied.

As shown in FIG. 4, in the oxide thin film transistor, the semiconductor layer is formed of an oxide such as IGZO. The structure of the oxide thin film transistor is briefly described as follows.

The gate electrode 111 is formed on the substrate 110a. The gate insulating layer 112 is formed on the gate electrode 111. An oxide semiconductor layer 113 is formed on the gate insulating film 112 corresponding to the gate electrode 111. The contact layer 114 is formed on the oxide semiconductor layer 113. Source and drain electrodes 115a and 115b are formed on the gate insulating layer 112 to contact the oxide semiconductor layer 113 and the contact layer 114.

The above-described oxide thin film transistor has a good advantage over an amorphous silicon thin film transistor (a-Si TFT) in terms of current mobility and off current. Therefore, the oxide thin film transistor can be easily reduced in size, reduced bezel area, and reduced power consumption, which is advantageous for developing a high quality display device.

However, in the oxide thin film transistor, a threshold voltage shift (Vth Shift) of the oxide thin film transistor is caused according to a bias temperature illumination (BTIS) environment as shown in FIG. 5. When the oxide thin film transistor receives a positive voltage continuously, the threshold voltage moves in the positive (PBTS) direction. On the other hand, when the oxide thin film transistor receives a negative voltage continuously, the threshold voltage moves in the negative (NBTS) direction. Accordingly, in the oxide thin film transistor, the initial characteristic of the threshold voltage is moved in the positive (PBTS) direction or the negative (NBTS) direction depending on which voltage is input to the gate electrode.

Referring to the driving characteristics of the shift register composed of an oxide thin film transistor as shown in FIG. 6, the bias temperature stress, which is a problem, is most strongly formed in the Q node and the QB node.

The bias temperature stress of the oxide thin film transistor is a gate bias applied to the gate electrode, which is dominant in the voltage level and time, and the threshold voltage shift due to the positive PBTS is more pronounced than the negative NBTS. Therefore, deterioration of the shift register composed of the oxide thin film transistor occurs as the bias temperature stress characteristics of the Q node and the QB node continue.

As shown in FIG. 7, when the bias temperature stress characteristics of the Q node and the QB node persist, the shift register composed of the oxide thin film transistor deteriorates with time. For example, referring to "OD" at a point in time after 315 hours (hr) compared to 50 hours (hr), the degree of deterioration of output characteristics can be known.

As a result, in the display device to which the oxide thin film transistor is applied, a turn-on and turn-off operation region is changed by the shift of the threshold voltage of the oxide thin film transistor, resulting in deterioration of device characteristics. Accordingly, since the oxide thin film transistor is abnormally operated without being turned on and off in a fixed voltage region, this causes poor driving of the display device, deterioration of display quality, and shortened lifetime.

According to an exemplary embodiment of the present invention, the threshold voltage detector and the threshold voltage compensator are compensated for to improve the degradation of the display device to which the oxide thin film transistor is applied, that is, the deterioration of characteristics caused by the shift of the threshold voltage of the oxide thin film transistor.

Hereinafter, the threshold voltage detection unit and the threshold voltage compensation unit will be described.

8 is a circuit diagram illustrating a threshold voltage detector and a threshold voltage compensator according to an exemplary embodiment of the present invention, FIG. 9 is a driving waveform diagram of the circuit shown in FIG. 8, and FIG. 10 is a sense transistor of FIG. 8. FIG. 11 is a diagram illustrating a threshold voltage detection principle using FIG. 11, and FIG. 11 is a simulation result of detecting a threshold voltage shift of a sensing transistor. to be.

As shown in FIG. 8, the threshold voltage detection unit 140A (B) includes a current input transistor Ti, a diode pass transistor Td, a sense transistor Ts, a gate control transistor Tg, and a current output transistor ( Tv) and discharge transistor Tr. The transistors Ti, Td, Ts, Tg, Tv, and Tr included in the threshold voltage detector 140A (B) are formed of an oxide thin film transistor.

The current input transistor Ti operates so that a constant current output from the current source of the threshold voltage compensator 150 is input through the current path. In the current input transistor Ti, a gate electrode is connected to the second signal line Vcon2, a drain electrode is connected to a current source of the threshold voltage compensator 150, and a source electrode is connected to the drain electrode of the sensing transistor Ts. This is connected.

The diode pass transistor Td operates to connect the drain electrode and the gate electrode of the sense transistor Ts to form a diode connection state. In the diode pass transistor Td, a gate electrode is connected to the second signal line Vcon2, a drain electrode is connected to the source electrode of the current input transistor Ti, and a source electrode is connected to the gate electrode of the sensing transistor Ts.

The sensing transistor Ts senses the movement of the threshold voltage in response to a constant current input through the current path. The sensing transistor Ts represents the threshold voltage shift characteristic of the oxide thin film transistor included in the display panel (one or more of the subpixel and the gate driver). The sensing transistor Ts has a gate electrode connected to the source electrode of the gate control transistor Tg, a drain electrode connected to the source electrode of the current input transistor Ti, and a source electrode connected to the drain electrode of the current output transistor Tv. do.

The gate control transistor Tg controls the gate electrode of the sensing transistor Ts so that the threshold voltage shifting characteristic of the sensing transistor Ts represents the threshold voltage shifting characteristic of the oxide thin film transistor included in the display panel. In the gate control transistor Tg, a gate electrode is connected to the first signal line Vcon1, a drain electrode is connected to a gate signal, and a source electrode is connected to the gate electrode of the sensing transistor Ts.

The current output transistor Tv operates to form an output path at a constant current output through the source electrode of the sense transistor Ts. In the current output transistor Tv, a gate electrode is connected to the second signal line Vcon2, a drain electrode is connected to the source electrode of the sensing transistor Ts, and a source electrode is connected to the low potential voltage line Vcom / GND. Here, the low potential voltage line Vcom / GND is selected as the common voltage Vcom or the ground voltage GND according to the structure of the display panel.

The discharge transistor Tr operates to discharge the sense voltage of the sense transistor Ts in response to the gate start signal supplied to the gate driver. In the discharge transistor Tr, a gate electrode is connected to the + 1th gate start signal line Vst (N + 1), and a drain electrode and a source electrode are connected to the drain electrode and the source electrode of the current output transistor Tv.

The threshold voltage detection unit 140A (B) described above includes the first control signal and the second control signal supplied through the first signal line Vcon1 and the second signal line Vcon2 supplied from the outside as shown in FIG. 9. Operate in response to The first control signal and the second control signal may be output from the threshold voltage compensator or from a timing controller for controlling the gate driver. The first control signal and the second control signal have opposite pulse relationships so as to alternate between logic high and logic low.

In FIG. 9, Vst (N) is the nth gate start signal for operating the Nth shift register of the gate driver, and Vst (N + 1) is the nth for operating Nth + 1th shift register of the gate driver. +1 gate start signal. Vout Dummy is a dummy output signal of the Nth shift register of the gate driver, and Reset is a signal of resetting the Nth shift register of the gate driver. The blank time is a period between the nth gate start signal and the n + 1th gate start signal, and means a blank period during which the gate signal is not supplied to the display panel. Here, the gate start signal, the first control signal and the second control signal are converted into a logic low or logic high state between the low potential voltage VSS and the high potential voltage VDD.

As shown in FIG. 9, the first control signal in a logic high state is supplied to the first signal line Vcon1 during a signal output period in which the gate signal of the Nth shift register is output. The gate control transistor Tg supplied with the first control signal in a logic high state is turned on. The turned-on gate control transistor Tg turns on the gate electrode of the sensing transistor Ts in response to the gate signal. That is, the gate control transistor Tg forms a bias temperature stress on the gate electrode of the sensing transistor Ts such that the threshold voltage shifting characteristic of the sensing transistor Ts represents the threshold voltage shifting characteristic of the oxide thin film transistor included in the display panel. do. At this time, the second control signal in a logic low state is supplied to the second signal line Vcon2. Therefore, the current input transistor Ti, the diode pass transistor Td and the current output transistor Tv are turned off during the signal output period during which the gate signal is output.

Thereafter, the second control signal in a logic high state is supplied to the second signal line Vcon2 during the blank period in which the gate signal of the Nth shift register is not output. The current input transistor Ti, the diode pass transistor Td, and the current output transistor Tv supplied with the second control signal in a logic high state are turned on. The turned-on current input transistor Ti inputs a constant current output from a current source of the threshold voltage compensator 150 through a current path. The turned-on diode pass transistor Td connects the drain electrode and the gate electrode of the sensing transistor Ts to form a diode connection state. A sensing voltage Vsense corresponding to a threshold voltage is formed in the sensing transistor Ts in a diode connection state. The turned-on current output transistor Tv is turned on so that an output path is formed at a constant current output through the source electrode of the sense transistor Ts. At this time, the first control signal in a logic low state is supplied to the first signal line Vcon1. Therefore, the gate control transistor Tg is turned off during the blank period in which the gate signal is not output.

Thereafter, the discharge transistor Tr is turned on in response to the N + 1th gate start signal supplied through the N + 1th gate start signal line Vst (N + 1) of the N + 1th shift register. The turned-on discharge transistor Tr discharges the sense voltage remaining across the drain electrode and the source electrode of the sense transistor Ts to increase the accuracy of sensing the threshold voltage of the sense transistor Ts.

As can be seen in FIGS. 9 and 10, the sense transistor Ts (a in FIG. 10), which is in a diode connection state, is a diode (b in FIG. 10) having an anode and a cathode in circuit. Same as Sensing Voltage Variation of the anode of the sensing transistor Ts in the diode connection state indicates the shift of the threshold voltage Vth_ts of the sensing transistor Ts. When the sensing voltage variation of the anode of the sensing transistor Ts, that is, the sensing voltage Vsense, is detected during the Vth sensing time, the threshold voltage of the oxide thin film transistor included in the display panel is detected. To compensate.

The threshold voltage compensator 150 detects a sensing voltage variation, that is, a sensing voltage Vsense of an anode of the sensing transistor Ts during the threshold voltage sensing period Vth sensing time. Accordingly, the threshold voltage compensator 150 determines whether the threshold voltage Vth_ts of the sensing transistor Ts is a negative shift (Vth Nega.Shift) or a positive shift (Vth Posi.Shift) based on the change of the sensing voltage Vsense. It is possible to determine whether to generate a compensation signal according to the determination result.

Meanwhile, in the embodiment, the reason for supplying a constant current to the anode of the sensing transistor Ts is as follows. In general, the diode connection of the thin film transistor cannot represent the negative shift of the threshold voltage. Therefore, the embodiment supplies a constant current and sets the initial voltage formed at the anode of the sensing transistor Ts as the reference voltage. As the bias temperature stress is applied, the threshold voltage (Vth_ts) of the sensing transistor (Ts) is negatively shifted (Vth) by comparing the voltage variation (Sensing Voltage Variation) appearing on the anode of the sensing transistor (Ts) with the initial voltage. Nega.Shift) or positive shift (Vth Posi.Shift).

As in the embodiment, the basis for determining the movement of the threshold voltage Vth_ts of the sensing transistor Ts by comparing the initial voltage formed in the anode of the sensing transistor Ts with the voltage variation (Sensing Voltage Variation) is as follows. Reference is made to the simulation results of FIG. 11.

As shown in FIG. 12, when the positive bias acts as a stress on the gate electrode, the threshold voltage is shifted to the right side compared to the initial setting. In contrast, in the oxide thin film transistor, when a negative bias acts as a stress on the gate electrode, the threshold voltage is shifted to the left of the initial setting.

From the driving voltage point of view, (A) the oxide thin film transistor having an initial value (Initial) in the voltage range shows a turn-off characteristic, whereas the NBTS oxide thin film transistor having a negatively shifted threshold voltage exhibits a turn-on characteristic. In addition, (B) oxide thin film transistors having initial values in the voltage region exhibit turn-on characteristics, whereas PBTS oxide thin film transistors in which the threshold voltage is positively shifted exhibit turn-off characteristics. The threshold voltage shift phenomenon of the oxide thin film transistor causes deterioration in proportion to the voltage level and time applied to the gate electrode.

As such, since the oxide thin film transistor moves the threshold voltage according to the bias temperature stress, when the oxide thin film transistor is composed of elements included in the display panel, malfunction and defects are caused.

The embodiment applies a bias temperature stress, determines whether the threshold voltage is shifted, and generates a compensation signal according to the determination result using a sensing transistor representing the threshold voltage shift characteristic of the oxide thin film transistor. .

For example, when the sensing transistor of the threshold voltage sensing unit 140A (B) is detected to have an NBTS oxide thin film transistor characteristic compared to an initial value, the threshold voltage compensating unit 150 moves the gate source voltage Vgs in the positive direction. Generate a compensation signal to move to (+). On the other hand, if it is detected that the sensing transistor of the threshold voltage detector 140A (B) has the characteristics of the PBTS oxide thin film transistor compared to the initial value, the threshold voltage compensator 150 moves the gate source voltage Vgs in the negative direction. Generate a compensation signal to move to (+).

The sensing transistor of the threshold voltage detector 140A (B) is formed to represent an oxide thin film transistor included in at least one of the subpixel and the gate driver. The threshold voltage compensator 150 generates a compensation signal based on the sensed voltage sensed by the threshold voltage detector 140A (B). Accordingly, the threshold voltage compensator 150 generates a compensation signal capable of compensating a driving voltage supplied to the gate driver, for example, a high potential voltage VDD, or generates a compensation signal capable of compensating a gate low voltage supplied to a subpixel. Can be generated.

Hereinafter, the shift register to which the embodiment is applied will be described.

13 is an exemplary circuit diagram of a shift register to which a threshold voltage detection unit is applied.

As illustrated in FIG. 13, the shift register includes a first transistor T1, a third s transistor T3s, a third n transistor T3n, a fourth transistor T4, a fifth transistor T5, and a fifth q transistor (5th transistor). T5q), pull-up transistor T6 and pull-down transistor T7s. The threshold voltage detector includes first and second current input transistors T3i and T7i, first and second diode pass transistors T3d and T7d, and first through sixth gate control transistors Tg1 through Tg6, and first through second threshold current transistors. And second current output transistors T3v and T7v and discharge transistor Tr. For example, the threshold voltage detector uses a pull-down transistor T7s included in the shift register as a sense transistor without using a separate sense transistor.

Since the configuration of the shift register shown in FIG. 13 is an example, the present invention is not limited thereto. The transistors T1, T3s, T3n, T4, T5, T5q, T6, and T7s included in the shift register shown in FIG. 13 and the transistors Tg1 to Tg6, T3i, T7i, T3d, T7d, T3v, T7v, and Tr) are formed of an oxide thin film transistor.

The transistors T1, T3s, T3n, T4, T5, T5q, T6, and T7s constituting the shift register shown in FIG. 13 will be briefly described as follows.

The first transistor T1 charges the Q node Q in response to the gate start signal supplied through the gate start signal line VST. The third n transistor T3n resets the Q node Q in response to the reset signal supplied through the reset signal line RST. The third s transistor T3s maintains the Q node Q at a low potential voltage supplied through the low potential voltage line VSS in response to the voltage of the QB node QB. The fourth transistor T4 charges the QB node QB to the voltage supplied through the high potential voltage line VDD in response to the second clock signal supplied through the second clock signal line CLKB. The fifth transistor T5 discharges the QB node QB to the low potential voltage supplied through the low potential voltage line VSS in response to the voltage of the Q node Q. The fifth q transistor T5q discharges the QB node QB in response to the gate start signal supplied through the gate start signal line VST. The pull-up transistor T6 outputs a clock signal supplied through the clock signal line CLK as a gate high voltage according to the voltage state of the Q node Q. The pull-down transistor T7s outputs the low potential voltage supplied through the low potential voltage line VSS as the gate low voltage according to the voltage state of the QB node QB.

The shift register described above outputs a gate high voltage gate signal as the Q node Q is charged and the pull-up transistor T6 is turned on when the gate start signal is supplied through the gate start signal line VST. Subsequently, when the second clock signal is supplied through the second clock signal line CLKB, the QB node QB is charged and the gate signal of the gate low voltage is output as the pull-down transistor T7s is turned on.

The embodiment shows that the threshold voltage sensing unit is applied as an example to improve the threshold voltage shift problem occurring in the pull-down transistor T7s and the third s transistor T3s of the shift register. The transistors Tg1 to Tg6, T3i, T7i, T3d, T7d, T3v, T7v, and Tr included in the threshold voltage detector illustrated in FIG. 13 will be briefly described as follows.

The first to sixth gate control transistors Tg1 to Tg6 correspond to the first control signal supplied through the first signal line Vcon1, and pull-down transistors T7s and third s transistors T3s corresponding to the sensing transistors. It is turned on so that a bias temperature stress is formed on the gate electrode.

The first and second current input transistors T3i and T7i are output from the current source Icc (described as Icc in FIG. 8) in response to the second control signal supplied through the second signal line Vcon2. A constant current is turned on to input through the current path.

The first and second diode pass transistors T3d and T7d form the third s transistor T3s and the pull-down transistor T7s in a diode connection state in response to the first control signal supplied through the first signal line Vcon1. Is turned on.

The first and second current output transistors T3v and T7v are output through source electrodes of the third s transistor T3s and the pull-down transistor T7s in response to the second control signal supplied through the second signal line Vcon2. The output path is turned on to form a constant current.

The discharge transistor Tr corresponds to the third transistor T3s and the pull-down transistor in response to the N + 1 gate start signal supplied through the N + 1 gate start signal line VST (N + 1) of the rear shift register. It is turned on to discharge the sense voltage remaining across the drain electrode and the source electrode of T7s.

When the shift register described above outputs a gate signal corresponding to the gate high voltage and the gate low voltage, the Q node Q and the QB node QB have opposite charging patterns. In the case of the gate signal, the gate low voltage is continuously supplied after the gate high voltage is supplied for each gate line. Accordingly, the pull-up transistor T6 is continuously subjected to negative bias temperature stress, while the pull-down transistor T7s is continuously subjected to positive bias temperature stress.

In the case of the shift register, the pull-down transistor T7s is used to maintain the gate low voltage for almost one frame period. As a result, the threshold voltages of the third s transistor T3s and the pull-down transistor T7s subjected to the sustained positive bias temperature stress are shifted in the positive direction.

However, when the threshold voltage sensing units Tg1 to Tg6, T3i, T7i, T3d, T7d, T3v, T7v, and Tr configured as in the embodiment are applied, the third s transistor T3s has a shape as described with reference to FIGS. And a threshold voltage shift of the pull-down transistor T7s. 8 to 12, the threshold voltage compensation unit may be used to compensate for the shift of the threshold voltage. For example, the threshold voltage compensator may compensate for the turn-on / turn-off characteristics of the third s transistor T3s and the pull-down transistor T7s through a compensation signal for adjusting the high potential voltage supplied through the high potential voltage VDD. .

Meanwhile, in the embodiment of FIG. 13, only compensation according to threshold voltage shifts of the third s transistor T3s and the pull-down transistor T7s of the shift register constituting the gate driver is described. However, the embodiment may compensate for the shift of the threshold voltage of the other transistors as well as the pull-up transistor Tup of the shift register constituting the gate driver. In addition, the embodiment may perform compensation according to the threshold voltage shift of the thin film transistor of the subpixel separately from the gate driver.

Hereinafter, various examples of applying the threshold voltage detection unit on the display panel will be described.

14 to 16 illustrate various examples of applying a threshold voltage detector on a display panel.

As illustrated in FIG. 14, the first gate driver 120A and the second gate driver 120B are disposed in the non-display area NA outside the display area AA of the display panel 110 in a gate-in-panel manner. It is formed separately. The first and second threshold voltage sensing units 140A and 140B are formed on the first and second sides of the first and second gate driving units 120A and 120B (the lower left and right sides of the display area in the drawing). do.

The first threshold voltage detection unit 140A is formed to detect the shift of the threshold voltages of the transistors constituting the first stage STG1 of the first gate driver 120A. In addition, the second threshold voltage detection unit 140B is formed to detect the shift of the threshold voltages of the transistors constituting the first stage STG1 of the second gate driver 120B.

In the drawing, the gate driver is divided into left and right non-display areas NA as an example. However, one of the first gate driver 120A and the second gate driver 120B may be omitted. In addition, the first and second threshold voltage detection units 140A and 140B form the first stage STG1 of the first gate driver 120A and the first stage STG1 of the second gate driver 120B. The sensing of the threshold voltage shift is taken as an example. However, the first and second threshold voltage detection units 140A and 140B may include at least one of the stages STG1 to STGm of the first gate driver 120A and the stages STG1 to STGm of the second gate driver 120B. It may be formed to detect the shift of the threshold voltage of the transistors constituting one or more of the. In addition, the first and second threshold voltage detectors 140A and 140B may further include a circuit for detecting a shift of threshold voltages of transistors constituting at least one of the subpixels SP.

As shown in FIG. 15, the first gate driver 120A and the second gate driver 120B are disposed in the non-display area NA outside the display area AA of the display panel 110 in a gate-in-panel manner. It is formed separately. In addition, the first and second gate drivers 120A and 120B are formed by separating the first and second threshold voltage sensing units 140A1 and 140Am and the second and second threshold voltage sensing units 140B1 and 140Bm for each stage STG1 to STGm. .

The first threshold voltage detectors 140A1 to 140Am are formed to individually detect threshold voltage shifts of the transistors constituting each stage STG1 to STGm of the first gate driver 120A. The second threshold voltage detectors 140B1 to 140Bm are formed to individually detect threshold voltage shifts of the transistors constituting the stages STG1 to STGm of the second gate driver 120B.

In the drawing, the gate driver is divided into left and right non-display areas NA as an example. However, one of the first gate driver 120A and the second gate driver 120B may be omitted. In addition, the first and second threshold voltage detectors 140A1 to 140Am and 140B1 to 140Bm may further include a circuit for detecting a shift of threshold voltages of transistors constituting at least one of the subpixels SP.

As shown in FIG. 16, the first gate driver 120A and the second gate driver 120B are disposed in the non-display area NA outside the display area AA of the display panel 110 in a gate-in-panel manner. It is formed separately. The first, second, and third threshold voltage detection units 140A, 140B, and 140C are divided on the third side of the first and second gate drivers 120A and 120B (the upper center of the display area in the drawing). It is formed.

The first threshold voltage detection unit 140A is formed to detect the shift of the threshold voltage of transistors constituting at least one of the stages STG1 to STGm of the first gate driver 120A. In addition, the second threshold voltage detector 140B is configured to detect the shift of the threshold voltage of transistors constituting at least one of the stages STG1 to STGm of the second gate driver 120B. In addition, the third threshold voltage detector 140C is formed to detect the shift of the threshold voltage of transistors constituting at least one of the subpixels SP of the display area AA.

Hereinafter, a driving method of a display device according to an exemplary embodiment of the present invention will be described.

17 is a flowchart illustrating a method of driving a display device according to an exemplary embodiment of the present invention.

An embodiment of the present invention is a method of driving a display device that compensates for a threshold voltage of an oxide thin film transistor included in at least one of a subpixel and a gate driver, which has a flow as shown in FIG. 17. The detailed description and operation of the circuit refer to FIGS. 8 to 12.

During the period in which the gate signal is supplied to the display panel, the first control signal having a logic high state is supplied to the gate control transistor Tg to form a bias temperature stress on the gate electrode of the sensing transistor Ts (S110).

During the blank time in which the gate signal is not supplied to the display panel, the first signal in a logic low state is supplied to stop the bias temperature stress on the gate electrode of the sensing transistor Ts (S120).

The current path is supplied by supplying a second control signal in a logic high state to the current input transistor Ti, the diode pass transistor Td, and the current output transistor Tv during a blank time when the gate signal is not supplied to the display panel. By supplying a constant current through and connecting the drain electrode and the gate electrode of the sense transistor (Ts) to form a diode connection state and detects the movement of the threshold voltage (Vth_ts) of the sense transistor (Ts). S130)

On the basis of the change in the sensing voltage Vsense formed at the drain electrode of the sensing transistor Ts, it is determined whether the threshold voltage of the sensing transistor Ts is negative or positive movement, and a compensation signal is supplied according to the determination result. S140)

Between the step S130 of detecting the movement of the threshold voltage and the step S140 of supplying the compensation signal, the gate start signal supplied to the gate driver is supplied to the discharge transistor so that the sensing voltage of the sensing transistor is discharged (S145).

In operation S140, the compensation signal is used to compensate for one or more of the driving voltage supplied to the gate driver and the gate low voltage supplied to the subpixel.

The embodiment of the present invention prevents deterioration of the device by using a circuit capable of detecting and compensating a threshold voltage shift of an oxide thin film transistor according to a bias temperature stress (BTIS) environment. There is an effect of providing a display device and a driving method thereof that can improve the driving failure of the display, prevent the display quality from deteriorating and improve the life.

While the present invention has been described in connection with what is presently considered to be practical exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, It will be understood that the invention may be practiced. It is therefore to be understood that the embodiments described above are to be considered in all respects only as illustrative and not restrictive. In addition, the scope of the present invention is indicated by the following claims rather than the detailed description. Also, all changes or modifications derived from the meaning and scope of the claims and their equivalents should be construed as being included within the scope of the present invention.

110: display panel 120A, 120B: gate driver
130: data driver 140A, 140B: threshold voltage detection unit
150: threshold voltage compensator Ti: current input transistor
Td: Diode Pass Transistor Ts: Sense Transistor
Tg: gate control transistor Tv: current output transistor
Tr: discharge transistor

Claims (12)

A display panel including a subpixel formed in the display area;
A gate driver formed in the non-display area of the display panel and supplying a gate signal to the sub pixel;
A threshold voltage detector formed on the display panel; And
A threshold voltage compensator for supplying a constant current to the threshold voltage detector and compensating a threshold voltage of an oxide thin film transistor included in at least one of the subpixel and the gate driver based on a change in voltage;
The threshold voltage detection unit
A sensing transistor configured to sense a movement of a threshold voltage in response to the constant current input through a current path;
A diode pass transistor connecting the drain electrode and the gate electrode of the sense transistor to form a diode connection state;
And a gate control transistor for forming a bias temperature stress in the sense transistor. The method of claim 1,
The threshold voltage compensation unit
When the sensing transistor is in the diode connection state, it is determined whether the threshold voltage of the sensing transistor is negative or positive based on the change of the sensing voltage formed at the drain electrode of the sensing transistor, and the compensation signal is supplied according to the determination result. Display device characterized in that. The method of claim 1,
The gate control transistor
And turning on and off the gate electrode of the sensing transistor so that the threshold voltage shifting characteristic of the sensing transistor represents the threshold voltage shifting characteristic of the oxide thin film transistor. The method of claim 1,
And the gate control transistor is turned off and the diode pass transistor is turned on during a blank period during which a gate signal is not supplied to the display panel. The method of claim 1,
The threshold voltage detection unit
A current input transistor turned on to input the constant current through the current path;
A current output transistor turned on to form an output path at the constant current output through the source electrode of the sensing transistor;
And a discharge transistor turned on to discharge the sensed voltage of the sense transistor in response to a gate start signal supplied to the gate driver. The method of claim 5,
The gate control transistor is turned on in response to a first control signal,
And the current input transistor, the diode pass transistor, and the current output transistor are turned on in response to a second control signal having a pulse opposite to the first control signal. 3. The method of claim 2,
The threshold voltage compensation unit
And a compensation for a driving voltage supplied to the gate driver. 3. The method of claim 2,
The threshold voltage compensation unit
And a gate low voltage supplied to the sub pixel. The method of claim 5,
Transistors included in the threshold voltage detector
And an oxide thin film transistor. A driving method of a display device for compensating a threshold voltage of an oxide thin film transistor included in at least one of a subpixel and a gate driver,
Supplying a first control signal in a logic high state to the gate control transistor during a period in which the gate signal is supplied to the display panel, thereby forming a bias temperature stress on the gate electrode of the sensing transistor;
Supplying a first signal in a logic low state to a blank period during which a gate signal is not supplied to the display panel to stop the bias temperature stress formed in the gate electrode of the sensing transistor;
The second control signal in a logic high state is supplied to the current input transistor, the diode pass transistor, and the current output transistor during the blank period in which the gate signal is not supplied to the display panel, thereby supplying a constant current through the current path, and simultaneously Connecting the drain electrode and the gate electrode to form a diode connection state and detecting a shift of the threshold voltage of the sensing transistor; And
Determining whether the threshold voltage of the sense transistor is negative or positive based on the change of the sensed voltage formed on the drain electrode of the sense transistor, and supplying a compensation signal according to the determination result. . The method of claim 10,
The step of supplying the compensation signal
And supplying a gate start signal supplied to the gate driver to a discharge transistor so that the sense voltage of the sense transistor is discharged. The method of claim 10,
The step of supplying the compensation signal
And at least one of a driving voltage supplied to the gate driver and a gate low voltage supplied to the subpixel using the compensation signal.

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