KR20110057427A - Organic electroluminescent display device and method of driving the same - Google Patents

Abstract

PURPOSE: An organic electroluminescent display device and driving method thereof are provided to adjust the coupling between capacitors connected to a driving transistor, thereby normally measuring the threshold voltage of the driving transistor. CONSTITUTION: A gate wire, a sensing wire, and a data wire cross on a substrate. A switching transistor(Tsw) is connected to the gate wire and the data wire. A storage capacitor(Cst) is connected to the switching transistor. A driving transistor(Tdr) is connected to the storage capacitor. A sensing transistor(Tse) is connected to the gate electrode, the drain electrode, and the sensing wire of the driving transistor.

Description

Organic electroluminescent display and its driving method {ORGANIC ELECTROLUMINESCENT DISPLAY DEVICE AND METHOD OF DRIVING THE SAME}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic light emitting display device, and more particularly, to an organic light emitting display device having a device configuration capable of compensating a threshold voltage variation of a driving transistor and a driving method thereof.

One of the new flat panel displays, the organic electroluminescent display device (OLED device) is a self-luminous type, so it has better viewing angle and contrast ratio than liquid crystal display device and does not require backlight. Light weight and thinness are possible, and it is advantageous in terms of power consumption. In addition, since it is possible to drive DC low voltage, fast response speed, and all solid, it is strong against external shock, wide use temperature range, and especially in terms of manufacturing cost. Such an organic light emitting display device is also referred to as an organic light emitting diode device (OLED device).

The organic light emitting display device is a deposition and encapsulation equipment because the process is very simple, unlike a liquid crystal display device or a plasma display panel device (PDP device).

In particular, in an active matrix type, a voltage controlling a current applied to the pixel region is charged in a storage capacitor, and the voltage is maintained until the next frame signal is applied. It is driven to maintain the light emitting state while one screen is displayed regardless of the number of gate wirings.

Therefore, in the active matrix system, since the same luminance is displayed even when a low current is applied, low power consumption, high definition, and large size can be obtained.

Hereinafter, the basic structure and operation characteristics of the active matrix organic light emitting display device will be described in detail with reference to the accompanying drawings.

1 is an equivalent circuit diagram of one pixel area of a conventional organic light emitting display device.

As shown in FIG. 1, a gate line GL and a data line DL defining a pixel area P are formed to cross each other in a conventional organic light emitting display device, and one pixel area P is switched. The transistor Tsw, the driving transistor Tdr, the storage capacitor Cst, and the light emitting diode Del are included.

The switching transistor Tsw is connected to the gate line GL and the data line DL, the driving transistor Tdr and the storage capacitor Cst are connected to the switching transistor Tsw, and the light emitting diode Del and the driving transistor are connected. Tdr is connected between the high potential voltage VDD and the low potential voltage VSS.

The switching transistor Tsw is turned on according to the gate signal supplied through the gate line GL to drive the data signal supplied through the data line DL to the driving transistor Tdr and the storage capacitor Cst. To pass).

The driving transistor Tdr is turned on according to a data signal to control an electric current flowing through the light emitting diode Del to display an image.

That is, the amount of current flowing through the light emitting diode Del is proportional to the magnitude of the data signal, and the intensity of light emitted by the light emitting diode Del is proportional to the amount of current flowing through the light emitting diode Del. ) Displays different gray scales according to the magnitude of the data signal, and as a result, the organic light emitting display displays an image.

The storage capacitor Cst maintains a charge corresponding to the data signal for one frame to maintain a constant amount of current flowing through the light emitting diode Del, and to maintain a constant gray level displayed by the light emitting diode Del. Do it.

Unlike the liquid crystal display device in which the transistor of the pixel area is turned on only for a relatively short time of one frame, in the organic light emitting display device, the light emitting diode (Del) emits light to display the gray level for a relatively long time. The data signal is applied to the gate electrode of the driving transistor Tdr and maintained in a turned-on state. The driving transistor Tdr may be deteriorated by the application of the data signal for a long time.

That is, the data signal of the same polarity is applied to the gate electrode of the driving transistor Tdr for a long time (gate bias stress) to deteriorate the interface characteristics between the gate electrode and the gate insulating film of the driving transistor Tdr, and as a result, the driving transistor Tdr Threshold voltage (Vth) is changed.

The variation of the threshold voltage of the driving transistor Tdr adversely affects the image quality of the organic light emitting display device, which will be described with reference to the accompanying drawings.

2 is a diagram illustrating a current-voltage (IV) characteristic curve according to a threshold voltage variation of a driving transistor of a conventional organic light emitting display device, wherein a current is a current flowing between a drain electrode and a source electrode, and the voltage is a gate electrode. And the voltage between the source electrode.

As shown in FIG. 2, the driving transistor (Tdr of FIG. 1) has a first characteristic curve G1 of the first threshold voltage Vth1 at an initial stage of operation of the organic light emitting display device. As the operation continues, the threshold voltage is gradually increased to change the driving transistor Tdr to have second and third characteristic curves G2 and G3 of the second and third threshold voltages Vth2 and Vth3. (Vth1 <Vth2 <Vth3)

The change in the current-voltage characteristic curve of the driving transistor Tdr means that different currents flow between the drain electrode and the source electrode for the same data signal applied to the gate electrode.

For example, in the driving transistor Tdr according to the first, second, and third characteristic curves G1, G2, and G3, the first, second, and third currents I1, respectively, may be applied to the same data voltage Vdata. I2 and I3 flow, and the intensity of light emitted by the light emitting diode (Del in FIG. 1) gradually decreases.

As a result, the pixel areas of the organic light emitting display display different gradations for the same data signal, and the image quality of the organic light emitting display is deteriorated.

In addition, the degree of deterioration of the driving transistor Tdr may be different depending on the manufacturing process of the driving transistor Tdr and the type of the display image, and may also be different depending on the area in one organic light emitting display device, thereby further solving. There is a side that is difficult to do.

As a pixel structure for compensating the threshold voltage fluctuation due to the deterioration of the driving transistor, a pixel structure for storing the fluctuation value of the threshold voltage in a capacitor has been proposed.

FIG. 3 is an equivalent circuit diagram of one pixel area of a conventional organic light emitting display for compensating threshold voltage variations, and FIG. 4 is a timing chart of various signals supplied to the organic light emitting display of FIG. .

As shown in FIG. 3, a conventional organic light emitting display device is disposed to be spaced apart from each other in parallel with the gate line GL and the data line DL, which define the pixel region P and cross the gate line GL. The sensing wiring SL and the starting wiring IL are formed, and one pixel region P includes the switching transistor Tsw, the driving transistor Tdr, the sensing transistor Tse, the starting transistor Tin, The storage capacitor Cst and the light emitting diode Del are included.

The switching transistor Tsw is connected to the gate line GL and the data line DL, and the storage capacitor Cst is connected between the switching transistor Tsw and the driving transistor Tdr, and the light emitting diode Del and the driving The transistor Tdr is connected between the high potential voltage VDD and the low potential voltage VSS.

In addition, the sensing transistor Tse is connected to the sensing wiring SL and the gate electrode and the drain electrode of the driving transistor Tdr, and the starting transistor Tin is the starting wiring IL, the gate electrode of the driving transistor Tdr, and It is connected to the start voltage VIN.

In the organic light emitting display device having such a pixel structure, the sensing transistor Tse is turned on before the data signal is applied to the driving transistor Tdr every frame to thereby turn on the gate electrode of the driving transistor Tdr. And a drain electrode, so that current flows from the gate electrode of the driving transistor Tdr to the source electrode through the drain electrode.

At this time, as the current flows in the driving transistor Tdr, the voltage of the gate electrode of the driving transistor Tdr gradually decreases, and finally, when the voltage of the gate electrode of the driving transistor Tdr becomes the threshold voltage Vth, the driving transistor ( The channel of Tdr) is closed and no more current flows.

That is, when the sensing transistor Tse is turned on, the gate electrode of the driving transistor Tdr is discharged until the threshold voltage Vth is reached, and the threshold voltage which is the final voltage of the gate electrode of the driving transistor Tdr is It is stored in the storage capacitor Cst.

After that, the switching transistor Tsw is turned on to supply the data signal to the storage capacitor Cst, and the data signal is added to the threshold voltage Vth stored in the storage capacitor Cst to form the driving transistor Tdr. By being applied to the gate electrode, a channel corresponding to the data signal is always generated in the driving transistor Tdr regardless of the variation of the threshold voltage Vth.

At this time, in order to properly measure the threshold voltage Vth, the voltage of the gate electrode of the driving transistor Tdr, that is, the voltage VA of the A node, before the sensing transistor Tse is turned on, the threshold of the driving transistor Tdr. It must be higher than the voltage Vth.

Accordingly, in the organic light emitting display having the pixel structure of FIG. 3, the start transistor Vin is turned on before the measurement of the threshold voltage Vth is started to generate a start voltage VIN that is greater than the threshold voltage Vth. The threshold voltage Vth is normally measured by applying the gate electrode of the driving transistor Tdr.

As shown in FIG. 4, during driving of the conventional organic light emitting display, the high potential voltage VDD and the low potential voltage VSS are maintained at the first and second voltages V1 and V2, respectively.

The start voltage VIN connected to the source electrode of the start transistor (Tin in FIG. 3) has a pulse of the third voltage V3 wider than the pulse of the start signal VIL and higher than the threshold voltage Vth at the beginning of the current frame. The start signal VIL applied to the gate electrode of the start transistor Tin through the start wiring (IL in FIG. 3) has a pulse so that the start transistor Tin is turned on at the beginning of the sensing signal VSL.

The sensing signal VSL applied to the gate electrode of the sensing transistor (Tse of FIG. 3) through the sensing wiring (SL of FIG. 3) has a pulse so that the sensing transistor Tse is turned on during the sensing period. The gate signal VGL applied to the gate electrode of the switching transistor (Tsw of FIG. 3) through GL of FIG. 3 has a pulse so that the switching transistor Tsw is turned on.

Therefore, when the sensing transistor Tsw is turned on, current flows from the gate electrode of the driving transistor Tdr to the source electrode through the drain electrode, and finally the potential of the gate electrode of the driving transistor Tdr is driven by the driving transistor Tdr. Becomes the threshold voltage Vth of the current frame, and the threshold voltage Vth is stored in the storage capacitor Cst.

When the switching transistor Tsw is turned on, the data signal VDL supplied to the data line DL of FIG. 3 is transferred to the storage capacitor Cst, and the threshold voltage (stored in the storage capacitor Cst) The voltage VDL + Vth combined with Vth is applied to the gate electrode of the driving transistor Tdr to write the data signal VDL to the driving transistor Tdr during the data writing period.

Thereafter, the light emitting diode Del emits light having a gray level corresponding to the data signal during the light emitting period of the current frame.

Here, in order to normally measure the threshold voltage Vth of the driving transistor Tdr during the sensing period, the start transistor Tin is provided by the start signal VIL supplied through the start wiring IL during the reset period of the initial sensing period. Since the start voltage VIN of the third voltage V3 is turned on and applied to the node A which is the gate electrode of the driving transistor Tdr, the third voltage V3 is higher than the threshold voltage Vth. The transistor Tse can normally measure the threshold voltage.

Due to the start voltage VIN, the sensing signal VSL, and the gate signal VGL, the voltage VA of the node A, which is the gate electrode of the driving transistor Tdr, changes as shown in the drawing.

First, when the start voltage VIN increases, the parasitic capacitance of the driving transistor Tdr, the sensing transistor Tse, and the start transistor Tin around the A node is coupled to the A node. The voltage VA has a peak and is discharged.

Thereafter, during the reset period corresponding to the pulse of the start signal VIL, the voltage VA of the node A becomes the third voltage by the start voltage VIN, and is driven during the sensing period after the pulse of the start signal VIL ends. As the drain electrode of the transistor Tdr is discharged to the source electrode through, the voltage VA of the node A gradually decreases to become the threshold voltage Vth of the driving transistor Tdr of the current frame, and the threshold voltage Vth is stored. Stored in the capacitor Cst.

Thereafter, the data signal VDL transmitted to the storage capacitor Cst by the gate signal VGL is added to the threshold voltage Vth and applied to the gate electrode of the driving transistor Tdr during the data writing period, so that the voltage of the node A VA becomes a sum VDL + Vth of the data signal VDL and the threshold voltage Vth, and a current corresponding to the difference between the voltage of the gate electrode and the threshold voltage Vth flows through the driving transistor Tdr. In the light emitting period, the light emitting diode Del emits light having a gray level corresponding to the data signal VDL.

However, in the threshold voltage compensation driving of the conventional organic light emitting display device using the start transistor Tin, the start signal VIL, and the start voltage VIN, the start voltage VIN and the start signal VIL are also used. Undesirable light emission such as the first and second light leakage portions L1 and L2 of 4 occurs.

That is, the section between the light emitting section of the previous frame and the light emitting section of the current frame is a section required for measuring the threshold voltage and preparing for the non-light emitting section in which the LED does not emit light.

However, in the first and second light leakage sections L1 and L2, the voltage of the node A becomes high, so that the driving transistor Tdr is turned on, and as a result, the current flows from the high potential voltage VDD to the low potential voltage VSS. Flows and unwanted light may be emitted from the light emitting diode Del.

Such light leakage increases the luminance in the black image, thereby deteriorating the contrast ratio of the organic light emitting display device.

In order to prevent this, the transistor may be connected between the source electrode of the driving transistor Tdr and the low potential voltage VSS to block the current flow to the driving transistor Tdr. In this case, the threshold voltage of the driving transistor Tdr Vth) Current path (current path) for the measurement must be formed separately, there is a problem that the manufacturing cost and defect rate increases and the aperture ratio decreases by the addition of a transistor for the formation of such an additional current path.

The present invention is to solve the above problems, in the organic light emitting display device, by adding a coupling capacitor to the sensing transistor and by adjusting the voltage variation of the gate electrode of the driving transistor by the coupling with the storage capacitor, An object of the present invention is to provide an organic light emitting display device and a driving method thereof, in which light leakage is prevented and the accuracy and contrast ratio of threshold voltage measurement are improved.

In order to achieve the object as described above, the present invention, the substrate; A gate wiring, a sensing wiring and a data wiring formed on the substrate to cross each other; A switching transistor connected to the gate wiring and the data wiring; A storage capacitor coupled to the switching transistor; A driving transistor coupled to the storage capacitor; A sensing transistor connected to the gate electrode and the drain electrode of the driving transistor and the sensing wiring; A coupling capacitor connected to the gate electrode and the source electrode of the sensing transistor and coupled to the storage capacitor to make a voltage of the gate electrode of the driving transistor higher than a threshold voltage of the driving transistor; An organic light emitting display device comprising a light emitting diode connected to the driving transistor and emitting light is provided.

The sensing transistor may be switched according to a sensing signal of the sensing wiring to control diode connection between the gate electrode and the drain electrode of the driving transistor.

In addition, at the start timing when the sensing signal is applied, the voltage variation ΔVA of the gate electrode of the driving transistor may include a capacitance Cst of the storage capacitor, a capacitance Cco of the coupling capacitor, and a voltage of the sensing signal. It can be determined to satisfy the expression "ΔVA = {Cco / (Cst + Cco)} * ΔVSL" by the variation amount ΔVSL.

In addition, at the start timing when the sensing signal is applied, the voltage VA of the gate electrode of the driving transistor due to the voltage variation ΔVA of the gate electrode of the driving transistor is equal to the total variation ΔVth of the threshold voltage. A relationship VA> ΔVth + Vth0 may be greater than the sum of the initial value Vth0 of the threshold voltage.

The sensing signal may have two or more pulses for turning on the sensing transistor.

In addition, the organic light emitting display device includes the light emitting diode and the driving transistor connected between a high potential voltage and a low potential voltage, and connected between the high potential voltage and the driving transistor to control a current flowing to the light emitting diode. It may further include a light emitting transistor.

The light emitting transistor may be switched by a light emitting signal, and the light emitting signal may turn off the light emitting diode while the sensing transistor is turned on.

The organic light emitting display device may further include a reference transistor connected between the switching transistor and the storage capacitor and switched by the sensing signal.

The present invention provides a method of driving an organic light emitting display device including a switching transistor, a driving transistor, a sensing transistor, a storage capacitor, a coupling capacitor, and a light emitting diode, wherein the sensing signal is applied to the sensing transistor. The voltage of the gate electrode of the driving transistor is made higher than the threshold voltage of the driving transistor by the coupling of the storage capacitor and the coupling capacitor at a start timing when a signal is applied, and the threshold voltage of the driving transistor is measured. Storing in a storage capacitor; Applying a gate signal to the switching transistor to add a data signal to the threshold voltage stored in the storage capacitor; And controlling the light emitting diode to emit light by applying the sum of the data signal and the threshold voltage to a gate electrode of the driving transistor.

The voltage variation ΔVA of the gate electrode of the driving transistor at the start timing when the sensing signal is applied is the capacitance Cst of the storage capacitor, the capacitance Cco of the coupling capacitor, and the voltage variation of the sensing signal. [Delta] VSL) can be determined to satisfy the formula " ΔVA = {Cco / (Cst + Cco)} * ΔVSL "

At the start timing when the sensing signal is applied, the voltage VA of the gate electrode of the driving transistor due to the voltage variation ΔVA of the gate electrode of the driving transistor is equal to the total variation ΔVth of the threshold voltage. A relationship VA> ΔVth + Vth0 may be greater than the sum of the initial value Vth0 of the threshold voltage.

In addition, the sensing signal may have two or more pulses for turning on the sensing transistor.

The measuring and storing of the threshold voltage of the driving transistor in the storage capacitor may include turning off a light emitting transistor connected between the high potential voltage and the driving transistor to block a current flowing through the light emitting diode. It may include.

The measuring and storing of the threshold voltage of the driving transistor in the storage capacitor may include turning on a reference transistor connected between the switching transistor and the storage capacitor to connect the drain electrode of the switching transistor. Securing and holding one electrode of the capacitor.

As described above, in the organic light emitting display device according to the present invention, by adjusting the coupling between the capacitors connected to the driving transistor, it is possible to reduce the transistor and the signal for measuring the threshold voltage of the driving transistor normally.

That is, by omitting a separate signal for measuring the threshold voltage of the driving transistor, light emission of the light emitting diode is minimized and light leakage is prevented when the threshold voltage is measured. As a result, the contrast ratio and the image quality of the organic light emitting display device can be improved.

In addition, the omission ratio of the organic light emitting display device may be improved by omitting another transistor for measuring the threshold voltage of the driving transistor.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 5 is a schematic diagram illustrating an active matrix type organic light emitting display device according to a first embodiment of the present invention, and FIG. 6 is an equivalent circuit diagram illustrating a structure of one pixel area of FIG. 5.

5 and 6, the organic light emitting display device 110 according to the first embodiment of the present invention includes an organic light emitting panel 120 for displaying an image and an organic light emitting panel 120. A gate driver circuit unit 130 for supplying a gate signal and a sensing signal to the gate driver; a data driver circuit unit 140 for supplying a data signal to the organic light emitting panel 120; a gate driver circuit unit 130 and a data driver circuit unit 140; The timing controller 150 generates and supplies a plurality of signals and power.

In the organic light emitting panel 120, the first to mth gate lines GL1 to GLm, the first to mth sensing wires SL1 to SLm, and the first to the first to mth gate lines, which cross each other and define the pixel region P, are defined. n data lines DL1 to DLn are formed, and in each pixel region P, a switching transistor Tsw, a driving transistor Tdr, a sensing transistor Tse, a storage capacitor Cst, a coupling capacitor Cco, The pixel element unit 122 formed of the light emitting diode Del is formed.

Although not illustrated, the organic light emitting panel 120 may include the first to mth gate lines GL1 to GLm, the first to mth sensing lines SL1 to SLm, and the first through mth deposition, photolithography, and the like. The first to nth data lines DL1 to DLn, the switching transistor Tsw, the driving transistor Tdr, the sensing transistor Tse, the storage capacitor Cst, the coupling capacitor Cco, and the light emitting diode Del are removed. The first substrate may be formed on the first substrate, and the second substrate may be bonded to cover the elements of the first substrate. The first through m-th gate lines GL1 through GLm and the first through mth deposition and photolithography may be formed. To mth sensing wirings SL1 to SLm, first to nth data wirings DL1 to DLn, switching transistors Tsw, driving transistors Tdr, sensing transistors Tse, storage capacitors Cst, and couplings. The capacitor Cco is formed on the first substrate, and the light emitting diode Del is formed on the second substrate. The elements of each substrate so as to face may be formed by laminating the first and second substrates.

Since the plurality of pixel regions have the same configuration, hereinafter, for convenience, the first to m th gate lines GL1 to GLm are the gate lines GL, and the first to m th sensing lines SL1 to SLm are sensed wires ( In the SL, the first to nth data lines DL1 to DLn are described as data lines DL.

The gate electrode and the source electrode of the switching transistor Tsw are connected to the gate line GL and the data line DL, respectively, to receive a gate signal (VGL of FIG. 7) and a data signal (VDL of FIG. 7), respectively. The capacitor Cst is connected between the drain electrode of the switching transistor Tsw and the gate electrode of the driving transistor Tdr.

That is, the switching transistor Tsw is switched according to the gate signal to control the input of the data signal VDL to the storage capacitor Cst, and the driving transistor Tdr is switched according to the voltage of the storage capacitor Cst to emit light. The current of the diode Del is controlled.

The gate electrode and the drain electrode of the driving transistor Tdr are respectively connected to the source electrode and the drain electrode of the sensing transistor Tse, and the gate electrode of the sensing transistor Tse is connected to the sensing wiring SL to sense a sensing signal (FIG. 7). VSL).

That is, the sensing transistor Tse is switched according to the sensing signal to control diode connection between the gate electrode and the drain electrode of the driving transistor Tdr.

The coupling capacitor Cco is connected between the gate electrode and the source electrode of the sensing transistor Tse, and the light emitting diode Del is connected between the high potential voltage VDD and the drain electrode of the driving transistor Tdr. The source electrode of the driving transistor Tdr is connected to the low potential voltage VSS.

Here, a connection point of the gate electrode, the storage capacitor Cst, and the coupling capacitor Cco of the driving transistor Tdr, which is an important factor in measuring the threshold voltage (Vth of FIG. 7), of the driving transistor Tdr is an A node. define.

The switching transistor Tsw is turned on according to the gate signal VGL supplied through the gate line GL, and the storage transistor Cst receives the data signal VDL supplied through the data line DL. The driving transistor Tdr is turned on according to the sum (VDL + Vth) of the data signal VDL and the threshold voltage Vth stored in the storage capacitor Cst and flows through the light emitting diode Del. Display the image by controlling the current.

That is, since the current corresponding to the difference between the voltage VDL + Vth and the threshold voltage Vth of the gate electrode flows through the driving transistor Tdr, the amount of current flowing through the light emitting diode Del is dependent on the size of the data signal VDL. Since the intensity of light emitted by the light emitting diode Del is proportional to the amount of current flowing through the light emitting diode Del, the pixel region P displays different gray scales according to the size of the data signal VDL. As a result, the organic light emitting display device can display an image.

Here, the storage capacitor Cst is a frame including a threshold voltage Vth measured by the turn-on of the sensing transistor Tse and a data signal VDL transferred by the turn-on of the switching transistor Tsw. ) To compensate for the variation of the threshold voltage (Vth) while maintaining the amount of current flowing through the light emitting diode Del and the gray level displayed by the light emitting diode Del.

In other words, the sensing transistor Tse is turned on before the data signal VDL is applied to the driving transistor Tdr through the storage capacitor Cst every frame so that the gate electrode of the driving transistor Tdr is turned on. And a drain electrode, so that current flows from the gate electrode of the driving transistor Tdr to the source electrode through the drain electrode.

At this time, as the current flows in the driving transistor Tdr, the voltage of the gate electrode of the driving transistor Tdr gradually decreases, and finally, when the voltage of the gate electrode of the driving transistor Tdr becomes the threshold voltage Vth, the driving transistor ( The channel of Tdr) is closed and no more current flows.

That is, when the sensing transistor Tse is turned on, the gate electrode of the driving transistor Tdr is discharged until the threshold voltage is reached, and the threshold voltage which is the final voltage of the gate electrode of the driving transistor Tdr is stored in the storage capacitor Cst. )

Thereafter, the switching transistor Tsw is turned on to supply the data signal to the storage capacitor Cst, and the data signal VDL is added to the threshold voltage Vth stored in the storage capacitor Cst to drive the drive transistor Tdr. By applying to the gate electrode of), a channel corresponding to the data signal VDL is always generated in the driving transistor Tdr regardless of the variation of the threshold voltage Vth.

At this time, in order to measure the threshold voltage Vth normally, the voltage of the gate electrode of the driving transistor Tdr, that is, the voltage VA of the node A, before the sensing transistor Tse is turned on, the threshold of the driving transistor Tdr. The organic light emitting display device according to an exemplary embodiment of the present invention has to be higher than the voltage Vth. Instead, the start transistor Tin and the start voltage VIN are added to the gate electrode of the driving transistor Tdr. The coupling of the connected capacitor is controlled so that the voltage VA of the node A is higher than the threshold voltage Vth.

The first embodiment of the present invention will be described with reference to the drawings a number of signals applied to the organic light emitting display device and the voltage of the A node.

FIG. 7 is a timing diagram illustrating voltages of a node and a plurality of signals supplied to an organic light emitting display device according to a first embodiment of the present invention.

As shown in FIG. 7, during driving of the organic light emitting display device according to the first embodiment of the present invention, the high potential voltage VDD and the low potential voltage VSS are respectively the first voltage V1 and the first voltage. The second voltage V2 is smaller than the voltage.

In addition, the sensing signal VSL applied to the gate electrode of the sensing transistor (Tse of FIG. 6) through the sensing wiring (SL of FIG. 6) has a pulse for turning on the sensing transistor Tse during the sensing period. The gate signal VGL applied to the gate electrode of the switching transistor (Tsw in FIG. 6) through the wiring (GL in FIG. 6) has a pulse for turning on the switching transistor Tsw.

Therefore, during the sensing period in which the sensing transistor Tsw is turned on, current flows from the gate electrode of the driving transistor Tdr to the source electrode through the drain electrode, and finally the potential of the gate electrode of the driving transistor Tdr is driven. The threshold voltage Vth of the current frame of the transistor Tdr becomes the threshold voltage Vth and is stored in the storage capacitor Cst.

During the data writing period in which the switching transistor Tsw is turned on, the data signal VDL supplied to the data line DL is transferred to the storage capacitor Cst, and the threshold stored in the storage capacitor Cst. The voltage VDL + Vth combined with the voltage Vth is applied to the gate electrode of the driving transistor Tdr.

Thereafter, the light emitting diode Del emits light of a gray level corresponding to the data signal VDL during the light emitting period of the current frame.

The voltage VA of the A node connected to the gate electrode of the driving transistor Tdr by the high potential voltage VDD, the low potential voltage VSS, the sensing signal VSL, and the gate signal VGL is shown in the figure. Change.

That is, at the start timing of the sensing period after the start of the current frame, coupling of capacitors connected to the node A is caused by the voltage change ΔVSL of the sensing signal VSL applied to the gate electrode of the sensing transistor Tse. As a result, a kickback voltage DELTA VA is generated at the node A so that the voltage VA at the node A becomes a third voltage V3.

In this case, for the normal measurement of the threshold voltage Vth, the third voltage V3, which is the voltage of the start timing of the sensing section of the node A, should be equal to or greater than the threshold voltage Vth of the driving transistor Tdr. In order to be able to compensate for all of the threshold voltages Vth changed by the continuous driving of the device, the third voltage V3 must be greater than the sum of the total variation ΔVth of the threshold voltage and the initial threshold voltage Vth0. (V3> ΔVth + Vth0)

Specifically, node A has a storage capacitor Cst, a coupling capacitor Cco, a parasitic capacitor Cgddr between the gate electrode and the drain electrode of the driving transistor Tdr, and a gate electrode and a source electrode of the driving transistor Tdr. There is a parasitic capacitor Cgsse between the gate electrode and the source electrode of the parasitic capacitor Cgsdr and the sensing transistor Tse, which is applied to one electrode of the coupling capacitor Cco and the gate electrode of the sensing transistor Tse. The charge of the node A is redistributed according to the voltage variation ΔVSL of the sensing signal VSL, and thus the node A has a voltage variation ΔVA satisfying Equation (1).

ΔVA = {(Cco + Cgsse) / (Cst + Cco + Cgsse + Cgddr + Cgsdr)} * ΔVSL-Expression (1)

If parasitic capacitors Cgsse, Cgddr and Cgsdr of the driving transistor Tdr and the sensing transistor Tse are negligibly small compared to the storage capacitor Cst and the coupling capacitor Cco, Equation (1) is approximate. It can be expressed as Equation (2).

ΔVA = {Cco / (Cst + Cco)} * ΔVSL-Formula (2)

Therefore, when the capacitance of the node A is sufficiently increased by adjusting the capacitances of the coupling capacitor Cco and the light emitting capacitor Cel, the voltage VA of the node A at the start timing of the sensing period becomes The third voltage V3 may be raised to be greater than the threshold voltage Vth of the driving transistor Tdr and larger than the sum of the total variation ΔVth of the threshold voltage and the initial threshold voltage Vth0. The threshold voltage Vth of the driving transistor Tdr may be measured normally.

For example, by increasing the capacitance of the coupling capacitor Cco, the voltage variation ΔVA of the A node may be increased.

In the organic light emitting display device according to the first exemplary embodiment of the present invention, since the conventional start voltage (VIN of FIG. 4) and the start signal (VIL of FIG. 4) are omitted, the conventional first and second light leakage parts (L1, L2) does not occur and as a result light leakage is prevented and the contrast ratio is improved.

The coupling capacitor Cco may include the gate electrode, the gate insulating layer, the source and drain electrodes of the switching transistor Tsw, the driving transistor Tdr, and the sensing transistor Tse, when the organic light emitting panel 120 is formed. It can be formed separately using a protective film or the like.

In addition, since the parasitic capacitor Cgsse between the coupling capacitor Cco and the gate electrode and the source electrode of the sensing transistor Tse is equivalent, the parasitic capacitor between the gate electrode and the source electrode of the sensing transistor Tse is equivalent. Intentionally forming Cgsse may serve as a coupling capacitor Cco.

When the coupling capacitor Cco is formed separately from the sensing transistor Tse, the capacitance satisfying the formula (1) or the formula (2) can be obtained by adjusting the area of the capacitor electrode and the dielectric constant of the dielectric, and the coupling capacitor When (Cco) is formed in the form of a parasitic capacitor of the sensing transistor Tse, the capacitance satisfying the formula (1) or (2) is adjusted by adjusting the overlapping area of the gate electrode and the source electrode of the sensing transistor Tse. You can get it.

As described above, in the organic light emitting display device 110 according to the first embodiment of the present invention, sensing is performed by adjusting the capacitance of the coupling capacitor Cco formed between the gate electrode and the source electrode of the sensing transistor Tse. At the start timing of the period, the voltage (node A: VA) of the gate electrode of the driving transistor Tdr is made higher than the threshold voltage Vth of the current frame by the voltage variation ΔVA due to the coupling. It can be formed higher than the sum (ΔVth + Vth0) of the total variation (ΔVth) and the initial threshold voltage (Vth0).

Accordingly, by omitting additional signals (a conventional start voltage and a start signal) for measuring the normal threshold voltage, it is possible to prevent light leakage during the threshold voltage measurement and to improve the contrast ratio and the image quality of the organic light emitting display device.

In addition, by omitting an additional transistor (a conventional start transistor) for normal threshold voltage measurement, the manufacturing cost and aperture ratio of the organic light emitting display device can be improved.

Meanwhile, in order to prevent the measurement error of the threshold voltage Vth of the driving transistor Tdr, the number of threshold voltages is measured by increasing the number of pulses of the sensing signal VSL applied to the organic light emitting display device having the pixel configuration of FIG. 6. It can be increased, which will be described with reference to the drawings.

8 is a timing diagram illustrating a plurality of signals supplied to an organic light emitting display device and a voltage of an A node according to a second embodiment of the present invention, which is a pixel structure of the organic light emitting display device according to the first embodiment. Applicable to FIG. 6, the description of the same parts as in FIG. 7 will be omitted.

As shown in FIG. 8, during driving of the organic light emitting display device according to the second embodiment of the present invention, the high potential voltage VDD and the low potential voltage VSS are respectively the first voltage V1 and the first voltage. The second voltage V2 is smaller than the voltage.

In addition, the sensing signal VSL applied to the gate electrode of the sensing transistor Tse of FIG. 6 through the sensing wiring SL may be configured to sense first and second sensing voltages in order to store a more accurate threshold voltage Vth. During the interval, the sensing transistor Tse has two pulses to turn on.

That is, the voltage of the gate electrode of the driving transistor Tdr may not be greater than the threshold voltage Vth due to a temporary cause at the start timing of the first sensing section. In this case, the correct threshold voltage Vth may be set in the first sensing section. Difficult to measure

In addition, although the voltage of the gate electrode of the driving transistor Tdr may not be sufficiently discharged due to a temporary cause during the first sensing period, even in this case, it is difficult to accurately measure the threshold voltage Vth in the first sensing period.

In the above two cases, the accuracy of the measurement of the threshold voltage Vth can be improved by re-measuring the threshold voltage Vth during the second sensing period after the temporary cause disappears.

For example, when the voltage of the node A is the third voltage V3 greater than the threshold voltage Vth at the end of the first sensing period, the sensing transistor Tse is again applied during the second sensing period after the first sensing period. By turning on, the voltage of the node A may be set to the threshold voltage Vth.

Although not shown, even when the voltage of the node A is smaller than the threshold voltage Vth at the end of the first sensing section, the voltage of the node A is turned on by turning on the sensing transistor Tse again in the second sensing section. It can be made to be the voltage (Vth).

Of course, even when the threshold voltage Vth is normally measured in the first sensing section, the normal threshold voltage Vth is measured again during the second sensing section, and the accuracy of the threshold voltage Vth measurement is not reduced.

After measuring the threshold voltage Vth twice, the gate signal VGL applied to the gate electrode of the switching transistor (Tsw in FIG. 6) through the gate wiring GL in FIG. 6 turns the switching transistor Tsw. To be turned on, the data signal VDL supplied through the data line DL of FIG. 5 is transferred to the storage capacitor Cst so that the data signal VDL and the threshold voltage Vth are summed (VDL + Vth). ) Is applied to the gate electrode of the driving transistor Tdr, whereby the data signal VDL is written to the driving transistor Tdr during the data writing period.

Thereafter, the light emitting diode Del emits light having a gray level corresponding to the data signal during the light emitting period of the current frame.

By the high potential voltage VDD, the low potential voltage VSS, the sensing signal VSL, and the gate signal VGL, the voltage VA of the A node connected to the drain electrode of the driving transistor Tdr is shown in FIG. Changes together.

That is, the capacitors connected to the node A by the voltage change ΔVSL of the sensing signal VSL applied to the gate electrode of the sensing transistor Tse at the start timing of each of the first and second sensing sections after the current frame starts. Coupling occurs, and a kickback voltage (ΔVA) is generated at node A according to Equation (1) or (2) so that the voltage VA of node A is finally fourth and fifth. Voltages V4 and V5 are obtained.

At this time, for the normal measurement of the threshold voltage Vth, the fourth voltage V4, which is the voltage VA of the node A at the start timing of the first sensing period, is the total variation amount ΔVth of the threshold voltage of the driving transistor Tdr. It must be greater than the sum of and the initial threshold voltage Vth0. (V4> ΔVth + Vth0)

However, due to a temporary cause, the fourth voltage V4 may be smaller than the threshold voltage Vth or the voltage of the node A may not be sufficiently discharged during the first sensing period. In this case, the voltage of the node A at the end timing of the first sensing period. The third voltage V3, which is VA, becomes larger or smaller than the threshold voltage Vth, thereby causing an error in the measurement of the threshold voltage Vth.

Accordingly, the voltage VA of the node A is increased by the variable voltage ΔVA by the voltage change ΔVSL of the sensing signal VSL during the second sensing period to be the fifth voltage V5, and then the threshold is once again. By measuring the voltage Vth, the voltage VA of the node A becomes the threshold voltage Vth at the end timing of the second sensing section.

In the second embodiment, the threshold voltage Vth is measured twice, but in another embodiment, the threshold voltage Vth may be measured two or more times to further improve accuracy.

As described above, in the organic light emitting display device according to the second embodiment of the present invention, the capacitance of the coupling capacitor Cco formed between the gate electrode and the source electrode of the sensing transistor Tse is adjusted to thereby adjust the first and the first and second electrodes. At the start timing of each of the two sensing periods, the voltage of the gate electrode (voltage of the node A: VA) of the driving transistor Tdr is higher than the threshold voltage Vth of the current frame by the voltage variation ΔVA due to the coupling. Furthermore, the sum of the total variation (ΔVth) of the threshold voltage and the initial threshold voltage (Vth0) may be higher than the sum (ΔVth + Vth0).

Accordingly, by omitting additional signals (a conventional start voltage and a start signal) for measuring the normal threshold voltage, it is possible to prevent light leakage during the threshold voltage measurement and to improve the contrast ratio and the image quality of the organic light emitting display device.

In addition, by omitting an additional transistor (a conventional start transistor) for normal threshold voltage measurement, the manufacturing cost and aperture ratio of the organic light emitting display device can be improved.

In addition, by turning on the sensing transistor two or more times and measuring the threshold voltage Vth two or more times, an error of the threshold voltage Vth measurement can be prevented and the accuracy of the threshold voltage Vth measurement can be improved.

Meanwhile, in order to prevent the light emitting diode from emitting light when the threshold voltage Vth is measured, a transistor blocking the voltage applied to the light emitting diode may be added to the pixel configuration of FIG. 6, which will be described with reference to the accompanying drawings.

FIG. 9 is an equivalent circuit diagram illustrating a structure of one pixel area of an organic light emitting display device according to a third embodiment of the present invention, and FIG. 10 illustrates a plurality of signals and node A supplied to the organic light emitting display device of FIG. 9. Is a timing diagram showing a voltage of FIG. 6 and a description of the same parts as in FIGS. 6 and 7 will be omitted.

9 and 10, the gate electrode and the source electrode of the switching transistor Tsw are connected to the gate line GL and the data line DL, respectively, so that the gate signal VGL and the data signal VDL are respectively. The storage capacitor Cst is connected between the drain electrode of the switching transistor Tsw and the gate electrode of the driving transistor Tdr.

That is, the switching transistor Tsw is switched according to the gate signal VGL to control the input of the data signal VDL to the storage capacitor Cst, and the driving transistor Tdr is switched according to the voltage of the storage capacitor Cst. The current of the light emitting diode Del is controlled.

The gate electrode and the drain electrode of the driving transistor Tdr are respectively connected to the source electrode and the drain electrode of the sensing transistor Tse, and the gate electrode of the sensing transistor Tse is connected to the sensing wire SL to sense the sensing signal VSL. Get supplied.

That is, the sensing transistor Tse is switched according to the sensing signal VSL to control diode connection between the gate electrode and the drain electrode of the driving transistor Tdr.

The coupling capacitor Cco is connected between the gate electrode and the source electrode of the sensing transistor Tse, and the light emitting diode Del is connected between the source electrode of the light emitting transistor Te and the drain electrode of the driving transistor Tdr. The source electrode of the driving transistor Tdr is connected to the low potential voltage VSS.

In addition, the gate electrode of the light emitting transistor Tem is connected to the light emitting wiring EL to receive the light emission signal VEL, and the drain electrode of the light emitting transistor Te is connected to the high potential voltage VDD.

That is, the light emitting transistor Tem is switched according to the light emitting signal to turn on / off a current of the light emitting diode Del.

Here, the connection point of the gate electrode, the storage capacitor Cst, and the coupling capacitor Cco of the driving transistor Tdr, which is an important factor for measuring the threshold voltage Vth of the driving transistor Tdr, is defined as an A node.

The switching transistor Tsw is turned on according to the gate signal VGL supplied through the gate line GL, and the storage transistor Cst receives the data signal VDL supplied through the data line DL. ), And the driving transistor Tdr is turned on according to the sum (VDL + Vth) of the data signal VDL and the threshold voltage Vth stored in the storage capacitor Cst and flows through the light emitting diode Del. Control to display the image.

That is, since the current corresponding to the difference between the voltage VDL + Vth and the threshold voltage Vth of the gate electrode flows through the driving transistor Tdr, the amount of current flowing through the light emitting diode Del is dependent on the size of the data signal VDL. Since the intensity of light emitted by the light emitting diode Del is proportional to the amount of current flowing through the light emitting diode Del, the pixel region P displays different gray scales according to the size of the data signal VDL. As a result, the organic light emitting display device can display an image.

Here, the storage capacitor Cst is a frame including a threshold voltage Vth measured by the turn-on of the sensing transistor Tse and a data signal VDL transferred by the turn-on of the switching transistor Tsw. ) To compensate for the variation of the threshold voltage (Vth) while maintaining the amount of current flowing through the light emitting diode Del and the gray level displayed by the light emitting diode Del.

In other words, the sensing transistor Tse is turned on before the data signal VDL is applied to the driving transistor Tdr through the storage capacitor Cst every frame so that the gate electrode of the driving transistor Tdr is turned on. And by connecting the drain electrode, a current flows from the gate electrode of the driving transistor Tdr to the source electrode through the drain electrode.

At this time, as the current flows in the driving transistor Tdr, the voltage of the gate electrode of the driving transistor Tdr gradually decreases, and finally, when the voltage of the gate electrode of the driving transistor Tdr becomes the threshold voltage Vth, the driving transistor ( The channel of Tdr) is closed and no more current flows.

That is, when the sensing transistor Tse is turned on, the gate electrode of the driving transistor Tdr is discharged until the threshold voltage is reached, and the threshold voltage which is the final voltage of the gate electrode of the driving transistor Tdr is stored in the storage capacitor Cst. )

Thereafter, the switching transistor Tsw is turned on to supply the data signal to the storage capacitor Cst, and the data signal VDL is added to the threshold voltage Vth stored in the storage capacitor Cst to drive the drive transistor Tdr. By applying to the gate electrode of), a channel corresponding to the data signal VDL is always generated in the driving transistor Tdr regardless of the variation of the threshold voltage Vth.

On the other hand, in the organic light emitting display according to the third embodiment of the present invention, the light emitting diode Tem is turned off while the threshold voltage Vth is measured by turning on the sensing transistor Tse. It cuts off the current flowing to (Del) and prevents light emission of the light emitting diode (Del).

That is, the light emitting transistor Tem is turned on during the light emitting period of each frame to pass a current flowing through the light emitting diode Del, and includes a non-light emitting period including a sensing period and a data writing period before the light emitting period of each frame. During the turn-off, the current flowing to the light emitting diode Del is blocked.

In addition, the high potential voltage VDD, the low potential voltage VSS, the sensing signal VSL, and the gate signal VGL are the same as in the first embodiment.

That is, during driving of the organic light emitting display device according to the third embodiment of the present invention, the high potential voltage VDD and the low potential voltage VSS are respectively the first voltage V1 and the second voltage smaller than the first voltage. If the sensing transistor Tse is turned on by the sensing signal VSL during the sensing period, the voltage VA of the node A is measured as the threshold voltage Vth and stored in the storage capacitor Cst. When the switching transistor Tsw is turned on by the gate signal VGL during the data writing period, the data signal VDL is transferred to the storage capacitor Cst, and the data signal VDL and the threshold voltage Vth. The sum VDL + Vth is applied to the gate electrode of the driving transistor Tdr so that the data signal is written to the driving transistor Tdr.

Thereafter, the light emitting diode Del emits light of a gray level corresponding to the data signal VDL during the light emitting period of the current frame.

The voltage VA of the A node connected to the gate electrode of the driving transistor Tdr by the high potential voltage VDD, the low potential voltage VSS, the sensing signal VSL, and the gate signal VGL is shown in the figure. Change.

That is, at the start timing of the sensing period after the start of the current frame, coupling of capacitors connected to the node A by the voltage change ΔVSL of the sensing signal VSL applied to the gate electrode of the sensing transistor Tse. ), And thus a kickback voltage (ΔVA) is generated at the node A, so that the voltage VA of the node A becomes a third voltage V3.

In this case, for the normal measurement of the threshold voltage Vth, the third voltage V3, which is the voltage of the start timing of the sensing section of the node A, should be equal to or greater than the threshold voltage Vth of the driving transistor Tdr. In order to be able to compensate for all of the threshold voltages Vth changed by the continuous driving of the device, the third voltage V3 must be greater than the sum of the total variation ΔVth of the threshold voltage and the initial threshold voltage Vth0. (V3> ΔVth + Vth0)

In addition, the light emission signal VEL supplied to the gate electrode of the light emitting transistor Tem maintains the fourth voltage V4 during the light emission period of each frame, and then, during the non-light emission period including the sensing period and the data writing period between the frames. The fifth voltage V5 smaller than the fourth voltage V4 is maintained.

Accordingly, the light emitting transistor Tem is turned on during the light emitting period and is turned off during the non-light emitting period. Since the switching of the light emitting transistor Tem does not affect the voltage VA of the A node, the threshold voltage Vth ) Is measured normally.

As described above, in the organic light emitting display device according to the third exemplary embodiment of the present invention, the sensing period is started by adjusting the capacitance of the coupling capacitor Cco formed between the gate electrode and the source electrode of the sensing transistor Tse. The voltage variation of the gate electrode of the driving transistor Tdr (voltage of the node A: VA) is higher than the threshold voltage Vth of the current frame by the voltage variation ΔVA due to the coupling at the timing, and thus the total variation of the threshold voltage. It can be formed higher than the sum (ΔVth + Vth0) of (ΔVth) and the initial threshold voltage (Vth0).

Accordingly, by omitting additional signals (a conventional start voltage and a start signal) for measuring the normal threshold voltage, it is possible to prevent light leakage during the threshold voltage measurement and to improve the contrast ratio and the image quality of the organic light emitting display device.

In addition, by omitting an additional transistor (a conventional start transistor) for normal threshold voltage measurement, the manufacturing cost and aperture ratio of the organic light emitting display device can be improved.

The light emitting transistor Tem is turned off during the non-light emitting period including the sensing period and the data writing period between the frames to prevent light emission of the light emitting diode Del in the non-light emitting period, thereby The contrast ratio can be further improved.

On the other hand, when the voltage of one electrode is changed in the storage capacitor connected to the switching transistor when the charge of the data signal of the previous frame remains on one electrode in the storage capacitor connected to the switching transistor, or when the threshold voltage is measured, the threshold voltage in the current frame Measurements can cause errors, so during the measurement of the threshold voltage of the current frame, the charge remaining on one electrode of the storage capacitor connected to the switching transistor is discharged and the voltage on one electrode remains fixed to the storage capacitor connected to the switching transistor. The pixel element unit may be configured, which will be described with reference to the accompanying drawings.

FIG. 11 is an equivalent circuit diagram illustrating a structure of one pixel area of an organic light emitting display device according to a fourth embodiment of the present invention, and FIG. 12 is an organic light emitting display device according to a fourth embodiment of the present invention. As a timing diagram showing a plurality of signals and voltages of the A node, the description of the same parts as in FIGS. 6 and 7 will be omitted.

As shown in FIGS. 11 and 12, the gate electrode and the source electrode of the switching transistor Tsw are connected to the gate line GL and the data line DL, respectively, to receive the gate signal VGL and the data signal, respectively. The storage capacitor Cst is connected between the drain electrode of the switching transistor Tsw and the gate electrode of the driving transistor Tdr.

That is, the switching transistor Tsw is switched according to the gate signal VGL to control the input of the data signal VDL to the storage capacitor Cst, and the driving transistor Tdr is switched according to the voltage of the storage capacitor Cst. The current of the light emitting diode Del is controlled.

The reference transistor Tre is connected between the switching transistor Tsw and the storage capacitor Cst.

That is, the gate electrode of the reference transistor Tre is connected to the sensing line SL to receive the sensing signal VSL, and the drain electrode and the source electrode of the reference transistor Tre are respectively the storage capacitor Cst and the reference voltage ( VRE).

Therefore, the reference transistor Tre is switched according to the sensing signal VSL, so that one electrode of the storage capacitor Cst connected to the drain electrode of the switching transistor Tse is fixed to the reference voltage VRE during the sensing period. To be maintained.

In addition, the gate electrode and the drain electrode of the driving transistor Tdr are connected to the source electrode and the drain electrode of the sensing transistor Tse, respectively, and the gate electrode of the sensing transistor Tse is connected to the sensing wiring SL so that the sensing signal ( VSL).

That is, the sensing transistor Tse is switched according to the sensing signal VSL to control diode connection between the gate electrode and the drain electrode of the driving transistor Tdr.

In addition, the coupling capacitor Cco is connected between the gate electrode and the source electrode of the sensing transistor Tse, and the light emitting diode Del is connected between the high potential voltage VDD and the drain electrode of the driving transistor Tdr. The source electrode of the driving transistor Tdr is connected to the low potential voltage VSS.

Here, the connection point of the gate electrode, the storage capacitor Cst, and the coupling capacitor Cco of the driving transistor Tdr, which is an important factor for measuring the threshold voltage Vth of the driving transistor Tdr, is defined as an A node.

The switching transistor Tsw is turned on according to the gate signal VGL supplied through the gate line GL to transfer the data signal supplied through the data line DL to the storage capacitor Cst. In addition, the driving transistor Tdr is turned on according to the sum (VDL + Vth) of the data signal VDL and the threshold voltage Vth stored in the storage capacitor Cst to control the current flowing through the light emitting diode Del. Display the video.

That is, since a current corresponding to the difference between the voltage VDL + Vth of the gate electrode and the threshold voltage Vth flows through the driving transistor Tdr, the amount of current flowing through the light emitting diode Del is the magnitude of the data signal VDL. Since the intensity of light emitted by the light emitting diode Del is proportional to the amount of current flowing through the light emitting diode Del, the pixel region P displays different gray scales according to the size of the data signal VDL. As a result, the organic light emitting display device may display an image.

Here, the storage capacitor Cst is a frame including a threshold voltage Vth measured by the turn-on of the sensing transistor Tse and a data signal VDL transferred by the turn-on of the switching transistor Tsw. ) To compensate for the variation of the threshold voltage (Vth) while maintaining the amount of current flowing through the light emitting diode Del and the gray level displayed by the light emitting diode Del.

In other words, the sensing transistor Tse is turned on before the data signal VDL is applied to the driving transistor Tdr through the storage capacitor Cst every frame so that the gate electrode of the driving transistor Tdr is turned on. And a drain electrode, so that current flows from the gate electrode of the driving transistor Tdr to the source electrode through the drain electrode.

At this time, as the current flows in the driving transistor Tdr, the voltage of the gate electrode of the driving transistor Tdr gradually decreases, and finally, when the voltage of the gate electrode of the driving transistor Tdr becomes the threshold voltage Vth, the driving transistor ( The channel of Tdr) is closed and no more current flows.

That is, when the sensing transistor Tse is turned on, the gate electrode of the driving transistor Tdr is discharged until the threshold voltage is reached, and the threshold voltage which is the final voltage of the gate electrode of the driving transistor Tdr is stored in the storage capacitor Cst. )

Thereafter, the switching transistor Tsw is turned on to supply the data signal to the storage capacitor Cst, and the data signal VDL is added to the threshold voltage Vth stored in the storage capacitor Cst to drive the drive transistor Tdr. By applying to the gate electrode of), a channel corresponding to the data signal VDL is always generated in the driving transistor Tdr regardless of the variation of the threshold voltage Vth.

Meanwhile, in the organic light emitting display device according to the fourth embodiment of the present invention, the reference transistor Tre is turned on while the threshold voltage Vth is measured by turning on the sensing transistor Tse, thereby switching. The voltage of one electrode of the storage capacitor Cst connected to the drain electrode of the transistor Tsw is maintained at the reference voltage VRE.

That is, the reference transistor Tre is turned on during the sensing period to connect one electrode of the storage capacitor Cst connected to the drain electrode of the switching transistor Tsw and the reference voltage VRE.

Charges corresponding to the data signal VDL of the previous frame may remain in one electrode of the storage capacitor Cst, and the voltage of one electrode of the storage capacitor Cst may fluctuate when the threshold voltage Vth is measured.

Since the voltage change in the remaining charge or sensing period of one electrode of the storage capacitor Cst may cause an error in the measurement of the threshold voltage Vth, in the organic light emitting display according to the fourth embodiment of the present invention, sensing is performed. By turning on the reference transistor Tre during the period to supply the reference voltage VRE to one electrode of the storage capacitor Cst, one electrode of the storage capacitor Cst is discharged, and the threshold voltage is fixed and maintained. (Vth) further improve the accuracy of the measurement.

In addition, the high potential voltage VDD, the low potential voltage VSS, the sensing signal VSL, and the gate signal VGL are the same as in the first embodiment.

That is, during driving of the organic light emitting display device according to the fourth embodiment of the present invention, the high potential voltage VDD and the low potential voltage VSS are respectively the first voltage V1 and the second voltage smaller than the first voltage. It is maintained at V2 and the reference voltage VRE is maintained at the fourth voltage V4.

When the sensing transistor Tse is turned on by the sensing signal VSL during the sensing period, the voltage VA of the node A is measured as the threshold voltage Vth and stored in the storage capacitor Cst. When the switching transistor Tsw is turned on by the gate signal VGL during the period, the data signal VDL is transferred to the storage capacitor Cst, and the sum of the data signal VDL and the threshold voltage Vth VDL + Vth is applied to the gate electrode of the driving transistor Tdr so that the data signal is written to the driving transistor Tdr.

Thereafter, the light emitting diode Del emits light of a gray level corresponding to the data signal VDL during the light emitting period of the current frame.

The voltage of the node A connected to the gate electrode of the driving transistor Tdr by the high potential voltage VDD, the low potential voltage VSS, the reference voltage VRE, the sensing signal VSL, and the gate signal VGL. VA changes as shown in the figure.

That is, at the start timing of the sensing period after the start of the current frame, coupling of capacitors connected to the node A is caused by the voltage change ΔVSL of the sensing signal VSL applied to the gate electrode of the sensing transistor Tse. As a result, a kickback voltage DELTA VA is generated at the node A so that the voltage VA at the node A becomes a third voltage V3.

In this case, for the normal measurement of the threshold voltage Vth, the third voltage V3, which is the voltage of the start timing of the sensing section of the node A, should be equal to or greater than the threshold voltage Vth of the driving transistor Tdr. In order to be able to compensate for all of the threshold voltages Vth changed by the continuous driving of the device, the third voltage V3 must be greater than the sum of the total variation ΔVth of the threshold voltage and the initial threshold voltage Vth0. (V3> ΔVth + Vth0)

In addition, the reference transistor Tre is turned on during the sensing period, and one electrode of the storage capacitor Cst connected to the drain electrode of the switching transistor Tsw is fixed to the fourth voltage V4 which is the reference voltage VRE. Since it is maintained, the accuracy of the threshold voltage Vth measurement using the variable voltage DELTA VA of the A node is further improved.

As described above, in the organic light emitting display device according to the fourth embodiment of the present invention, the sensing period is started by adjusting the capacitance of the coupling capacitor Cco formed between the gate electrode and the source electrode of the sensing transistor Tse. The voltage variation of the gate electrode of the driving transistor Tdr (voltage of the node A: VA) is higher than the threshold voltage Vth of the current frame by the voltage variation ΔVA due to the coupling at the timing, and thus the total variation of the threshold voltage. It can be formed higher than the sum (ΔVth + Vth0) of (ΔVth) and the initial threshold voltage (Vth0).

Accordingly, by omitting additional signals (a conventional start voltage and a start signal) for measuring the normal threshold voltage, it is possible to prevent light leakage during the threshold voltage measurement and to improve the contrast ratio and the image quality of the organic light emitting display device.

In addition, by omitting an additional transistor (a conventional start transistor) for normal threshold voltage measurement, the manufacturing cost and aperture ratio of the organic light emitting display device can be improved.

In addition, the voltage of one electrode of the storage capacitor Cst connected to the drain electrode of the switching transistor Tsw is fixedly maintained during the sensing period, thereby preventing an error in the measurement of the threshold voltage Vth and the threshold voltage Vth. The accuracy of the measurement can be improved.

6, 9, and 11 illustrate a case in which the transistor of the pixel element portion is a negative type, but in another embodiment, the pixel element portion may be configured as a positive type transistor. The position of the diode is changed between the driving transistor and the low potential voltage, and the remaining elements can be configured in the same manner as in the case of the negative type.

On the other hand, when the sensing transistor is turned on, the gate electrode and the drain electrode of the driving transistor are connected, so that the current flowing through the driving transistor by controlling the voltage of the gate electrode of the driving transistor is controlled by controlling the voltage of the drain electrode of the driving transistor. This can have the same effect as flowing a current through the transistor.

Therefore, in the first to fourth embodiments of the present invention, a coupling capacitor is formed between the gate electrode and the source electrode of the sensing transistor to control the voltage of the gate electrode of the driving transistor to a voltage higher than the threshold voltage at the start timing of the sensing period. Although the threshold voltage was measured, in another embodiment, a coupling capacitor was formed between the gate electrode and the drain electrode of the sensing transistor to control the voltage of the drain electrode of the driving transistor to a voltage higher than the threshold voltage at the start timing of the sensing period. You can also measure voltage.

The present invention is not limited to the above embodiments, and various modifications can be made without departing from the spirit of the present invention.

1 is an equivalent circuit diagram of one pixel area of a conventional organic light emitting display device.

2 is a diagram illustrating a current-voltage (I-V) characteristic curve according to a threshold voltage variation of a driving transistor of a conventional organic light emitting display device.

3 is an equivalent circuit diagram of one pixel area of a conventional organic light emitting display device to compensate for threshold voltage variations.

4 is a timing diagram of various signals supplied to the organic light emitting display device of FIG. 3.

5 is a schematic diagram illustrating an organic light emitting display device of an active matrix type according to a first embodiment of the present invention.

FIG. 6 is an equivalent circuit diagram illustrating a structure of one pixel area of FIG. 5. FIG.

FIG. 7 is a timing diagram showing voltages of a plurality of signals and node A supplied to an organic light emitting display device according to a first embodiment of the present invention; FIG.

8 is a timing diagram illustrating voltages of a plurality of signals and an A node supplied to an organic light emitting display device according to a second embodiment of the present invention;

9 is an equivalent circuit diagram illustrating a structure of one pixel area of an organic light emitting display device according to a third exemplary embodiment of the present invention.

FIG. 10 is a timing diagram illustrating voltages of a node and a plurality of signals supplied to the organic light emitting display device of FIG. 9; FIG.

11 is an equivalent circuit diagram illustrating a structure of one pixel area of an organic light emitting display device according to a fourth embodiment of the present invention.

12 is a timing diagram showing voltages of a plurality of signals and node A supplied to an organic light emitting display device according to a fourth embodiment of the present invention;

Claims (14)

A substrate; A gate wiring, a sensing wiring and a data wiring formed on the substrate to cross each other; A switching transistor connected to the gate wiring and the data wiring; A storage capacitor coupled to the switching transistor; A driving transistor coupled to the storage capacitor; A sensing transistor connected to the gate electrode and the drain electrode of the driving transistor and the sensing wiring; A coupling capacitor connected to the gate electrode and the source electrode of the sensing transistor and coupled to the storage capacitor to make a voltage of the gate electrode of the driving transistor higher than a threshold voltage of the driving transistor; Light emitting diodes connected to the driving transistors to emit light An organic light emitting display device comprising a. The method of claim 1, And the sensing transistor is switched according to a sensing signal of the sensing wiring to control diode connection between the gate electrode and the drain electrode of the driving transistor. The method of claim 2, The voltage variation ΔVA of the gate electrode of the driving transistor at the start timing when the sensing signal is applied is the capacitance Cst of the storage capacitor, the capacitance Cco of the coupling capacitor, and the voltage variation of the sensing signal. An organic light emitting display device determined to satisfy the formula " ΔVA = {Cco / (Cst + Cco)} * ΔVSL " The method of claim 3, wherein At the start timing when the sensing signal is applied, the voltage VA of the gate electrode of the driving transistor due to the voltage variation ΔVA of the gate electrode of the driving transistor is equal to the total variation ΔVth of the threshold voltage and the threshold. An organic light emitting display device (VA> ΔVth + Vth0) that is greater than the sum of the initial values (Vth0) of voltages. The method of claim 2, And the sensing signal has two or more pulses for turning on the sensing transistor. The method of claim 2, The light emitting diode and the driving transistor are connected between a high potential voltage and a low potential voltage, the organic light emitting diode further comprises a light emitting transistor connected between the high potential voltage and the driving transistor to control the current flowing to the light emitting diode. Display. The method of claim 6, The light emitting transistor is switched by a light emitting signal, and the light emitting signal turns off the light emitting diode while the sensing transistor is turned on. The method of claim 2, And a reference transistor connected between the switching transistor and the storage capacitor and switched by the sensing signal. In the driving method of an organic light emitting display device comprising a switching transistor, a driving transistor, a sensing transistor, a storage capacitor, a coupling capacitor and a light emitting diode, A sensing signal is applied to the sensing transistor to make the voltage of the gate electrode of the driving transistor higher than the threshold voltage of the driving transistor by coupling the storage capacitor and the coupling capacitor at a start timing when the sensing signal is applied. Measuring the threshold voltage of the driving transistor and storing the threshold voltage in the storage capacitor; Applying a gate signal to the switching transistor to add a data signal to the threshold voltage stored in the storage capacitor; Controlling the light emitting diode to emit light by applying the sum of the data signal and the threshold voltage to a gate electrode of the driving transistor; Method of driving an organic light emitting display device comprising a. The method of claim 9, The voltage variation ΔVA of the gate electrode of the driving transistor at the start timing when the sensing signal is applied is the capacitance Cst of the storage capacitor, the capacitance Cco of the coupling capacitor, and the voltage variation of the sensing signal. A method of driving an organic light emitting display device determined to satisfy the formula " ΔVA = {Cco / (Cst + Cco)} * ΔVSL " 11. The method of claim 10, At the start timing when the sensing signal is applied, the voltage VA of the gate electrode of the driving transistor due to the voltage variation ΔVA of the gate electrode of the driving transistor is equal to the total variation ΔVth of the threshold voltage and the threshold. A method of driving an organic light emitting display device (VA> ΔVth + Vth0), which is greater than the sum of the initial value Vth0 of the voltage. The method of claim 9, And wherein the sensing signal has at least two pulses for turning on the sensing transistor. The method of claim 9, Measuring and storing the threshold voltage of the driving transistor in the storage capacitor includes turning off a light emitting transistor connected between the high potential voltage and the driving transistor to block a current flowing through the light emitting diode. A method of driving an organic light emitting display device. The method of claim 9, Measuring and storing the threshold voltage of the driving transistor in the storage capacitor may include turning on a reference transistor connected between the switching transistor and the storage capacitor to connect the drain electrode of the switching transistor. A method of driving an organic light emitting display device comprising fixing and holding one electrode.

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