KR101411805B1 - Method of driving an organic light emitting display device - Google Patents

Abstract

A driving method of an organic light emitting display device is disclosed.

The present invention can charge the threshold voltage of the driving transistor to the storage capacitance so that the driving current of the driving transistor is determined only by the data voltage and the black data so that the luminance uniformity of each pixel can be maintained.

According to the present invention, the threshold voltage of the driving transistor shifted by the deterioration due to the data voltage can be restored to the original gray voltage by the black data, and the image quality can be improved.

Organic light emission, display device, luminance unevenness, deterioration, black data

Description

TECHNICAL FIELD [0001] The present invention relates to a method of driving an organic electro-luminescence display device,

BACKGROUND OF THE INVENTION 1. Field of the Invention [0002] The present invention relates to an organic light emitting display, and more particularly, to a driving method of an organic light emitting display.

Due to the development of the information society, display devices capable of displaying information are actively being developed. The display device includes a liquid crystal display device, an organic electro-luminescence display device, a plasma display panel, and a field emission display device.

Among them, the organic light emitting display device has advantages that the thickness is minimized and the power consumption is reduced since a backlight unit is not required unlike a liquid crystal display device.

In an organic light emitting display, a plurality of pixels are arranged in a matrix. Each pixel includes a switching transistor, a storage capacitance, a driving transistor, and an organic light emitting diode.

A data voltage is supplied to the driving transistor by switching of the switching transistor, and a driving current is generated in the driving transistor by the data voltage, and the organic light emitting diode emits light by the driving current. The storage capacitance serves to maintain the data voltage for one frame.

The driving transistor has a threshold voltage. In order for the driving current to be generated in the driving transistor, the voltage between the gate terminal and the source terminal of the driving transistor must be larger than the threshold voltage.

A data voltage having the same polarity is supplied to the gate terminal of the driving transistor every frame. The gate terminal of the driving transistor is deteriorated by the data voltage of the same polarity, and the threshold voltage is shifted.

Since the shifted threshold voltage can not be restored to the original threshold voltage as the data voltage of the same polarity is supplied for every frame, the driving current of the driving transistor is changed by a different threshold voltage, There is a problem that luminance unevenness is caused.

Accordingly, it is an object of the present invention to provide a driving method of an organic light emitting display device capable of preventing deterioration and preventing luminance unevenness.

According to a first embodiment of the present invention there is provided a display device comprising a plurality of pixels arranged in a matrix, each pixel comprising a switching transistor connected between a gate line, a data line and a first node, A driving transistor connected between the first node and the second node, a storage capacitance connected between the first node and the second node, and an organic light emitting diode connected to the second node, Charging a second node with a low-level power voltage supplied to the line; The switching transistor is turned on by the first scan pulse supplied to the gate line and the black data supplied to the data line is charged to the first node via the switching transistor while the high voltage supplied to the voltage supply line Level power voltage is supplied to the driving transistor, and charging the storage capacitance with a threshold voltage of the driving transistor; Supplying a data voltage supplied to the data line to the driving transistor via the switching transistor; And emitting the organic light emitting diode by a driving current generated in the driving transistor, wherein the driving current is determined by the data voltage and the black data.

The present invention can charge the threshold voltage of the driving transistor to the storage capacitance so that the driving current of the driving transistor is determined only by the data voltage and the black data so that the luminance uniformity of each pixel can be maintained.

According to the present invention, the threshold voltage of the driving transistor shifted by the deterioration due to the data voltage can be restored to the original gray voltage by the black data, and the image quality can be improved.

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

1 is a view illustrating an organic light emitting diode display according to the present invention.

Referring to FIG. 1, the OLED display includes an OLED display panel 40, a gate driver 10, a data driver 20, and a voltage supplier 30.

The organic light emitting display panel 40 includes a plurality of pixels 42 arranged in a matrix.

The organic light emitting display panel 40 is arranged such that a plurality of gate lines GL and a plurality of data lines DL cross each other. The organic light emitting display panel 40 may include a plurality of voltage supply lines DD.

Each pixel 42 may be provided with one gate line GL, one data line DL, and one voltage supply line DD.

2 is a circuit diagram showing the pixel of Fig. 2 is a circuit diagram showing one pixel of a plurality of pixels.

The switching transistor Tl is electrically connected between the gate line GL, the data line DL and the first node n1.

The driving transistor T2 is electrically connected between the first node n1, the voltage supply line DD and the second node n2.

A storage capacitance Cst may be formed between the first and second nodes n1 and n2.

And the organic light emitting diode OLED may be electrically connected to the second node n2.

The gate signal Vs including two scan pulses (hereinafter, referred to as first and second scan pulses Vsp1 and Vsp2) may be supplied to each gate line GL during one frame. Each of the scan pulses Vsp1 and Vsp2 may be 1/2 of one horizontal period (1H).

The gate driver 10 generates and supplies two scan pulses Vsp1 and Vsp2 to each gate line GL.

The voltage supply line DD is supplied with the low level VDL within the range of the width of the first scan pulse Vsp1 after the rising time of the first scan pulse Vsp1 before the rising time of the first scan pulse Vsp1 And a first power voltage Vpower having a high level VDH can be supplied.

The voltage supply unit 30 supplies a single low level (VDL) to each voltage supply line DD.

The data voltage Vdn is supplied to the data line DL so that the first scan pulse Vsp1 overlaps at least the first section and the black data Vblack is supplied to overlap the second scan pulse Vsp2 at least during the second section. do.

The data voltage Vdn may be maintained from the first period before the polling time of the first scan pulse Vsp1 to a certain period after the polling time of the first scan pulse Vsp1.

The black data Vblack may continue from the second period before the polling time of the second scan pulse Vsp2 to a certain period after the polling time of the second scan pulse Vsp2. A third period of the width of the second scan pulse Vsp2 excluding the second period may be supplied with a data voltage Vdm to be supplied to another gate line.

The data driver 20 generates black data Vblack overlapped with the first period of the first scan pulse Vsp1 and the second period of the overlapped data voltage Vdn and the second scan pulse Vsp2, (DL).

The waveforms of these respective signals are shown in Fig.

A driving method of the organic light emitting display according to the present invention will be described based on such waveforms.

During the first period (1), the first power voltage Vpower is transitioned from the high level (VDH) to the low level (VDL). That is, the voltage supply unit 30 supplies the power supply voltage Vpower having the low level VDL to the voltage supply line DD.

The low level VDL may be at least lower than the second power voltage VSS. The second power voltage VSS may be generated at the power supply unit or may be generated at a separate power supply unit. The second power voltage VSS may be electrically connected to the organic light emitting diode OLED of each pixel 42. [

And a power voltage having a low level VDL is supplied to the driving transistor T2. In this case, since the low level VDL is lower than the second power voltage VSS, the second node n2 is charged to the low level VDL via the driving transistor T2.

The first section (1) may be determined in consideration of the threshold voltage value of the driving transistor T2. For example, when the threshold voltage of the driving transistor T2 becomes large, it takes a long time to fully charge the second node n2 to the low level VDL. Therefore, ) Can be long.

The first scan pulse Vsp1 is supplied to the switching transistor Tl through the gate line GL and the black data Vblack is supplied to the switching transistor Tl through the data line DL during the second period T1.

The black data Vblack may be at least higher than the low level VDL.

The switching transistor T1 is turned on by the first scan pulse Vsp1 so that the black data Vblack is supplied to the first node n1 connected to the gate terminal of the driving transistor T2 through the switching transistor T1 .

During the third period (3), the black data Vblack is continuously supplied to the first node n1 through the switching transistor T1 and the first power voltage Vpower is changed from the low level VDL to the high level VDH). That is, the voltage supply unit 30 supplies the first power voltage Vpower having the high level VDH to the driving transistor T2 through the voltage supply line DD.

When the first power voltage Vpower transitions from the low level VDL to the high level VDH in the third period ③, the second node n2 receives the black data Vblack from the driving transistor T2 A value (Vblack-Vth) obtained by subtracting the threshold voltage Vth can be charged.

Therefore, since the potential difference between the voltage of the first node n1 and the voltage of the second node n2 is charged in the storage capacitance Cst, the voltage Vblack of the first node n1 to the voltage of the second node n2, The threshold voltage Vth of the driving transistor T2, which is a potential difference between the voltage Vblack-Vth of the driving transistor T2, can be charged.

In other words, during the second and third periods (2, 3), the storage capacitance Cst can be charged with the threshold voltage Vth of the driving transistor T2.

During the fourth period (4), the data voltage Vdn is supplied to the data line DL. The data voltage Vdn is supplied to the first node n1 via the switching transistor T1.

At this time, the voltage Vn2 of the second node n2 may be expressed by the following equation (1).

Vn2 = (Vblack-Vth) + (Vdata-Vblack) * Cst / (Cst + Coled)

Here, Coled represents the capacitance of the organic light emitting diode (OLED).

In this case, the voltage of the storage capacitance Cst may be (Vdata-Vblack) * Coled / (Cst + Coled) + Vth.

During the fifth period (5), the first scan pulse Vsp1 is turned off. The fifth section (5) may have a range from the supply of the data voltage (Vdn) to the supply of the other data voltage (Vdm). The other data voltage Vdm may be supplied from the gate line GL to the pixel of the gate line before the predetermined range. The predetermined range may be the tenth previous gate line from the current gate line, or may be the gate line before the twentieth gate.

Even if the first scan pulse Vsp1 is turned off, the voltage of the storage capacitance Cst can be maintained as it is. The voltage of the storage capacitance Cst may be the voltage between the gate terminal and the source terminal of the driving transistor T2.

Therefore, the driving current Id of the driving transistor T2 can be expressed by the following equation (2).

Id = 1/2 * K * (Vgs-Vth) 2 = 1/2 * K * ((Vdata-Vblack) * Coled / (Cst + Coled) + Vth-Vth) 2

= 1/2 * K * ((Vdata-Vblack) * Coled / (Cst + Coled)) ²

Here, K is a constant.

Typically, assuming that Coled is much larger than Cst, Id = 1/2 * K * (Vdata-Vblack) ² .

Therefore, since the black data Vblack is a constant set value, the driving current Id is substantially dependent only on the data voltage Vdata. The data voltage Vdata may be substantially the data voltages Vdn and Vdm capable of expressing the gradation.

Therefore, the driving current Id of the present invention is constant regardless of the threshold voltage of the driving transistor T2, the second power voltage VSS or the change of the second node n2 due to deterioration of the organic light emitting diode OLED Value can be maintained.

During the sixth period (6), the second scan pulse Vsp2 is supplied to the gate line GL and the other data voltage Vdm is supplied to the data line DL. The other data voltage Vdm is a data voltage supplied from the gate line GL to a pixel on the gate line before a predetermined range but the switching transistor T1 is turned on by the second scan pulse Vsp2, n1. However, even if a different data voltage Vdm is supplied to the first node n1, the driving current of the driving transistor T2 does not change.

The organic light emitting diode OLED may emit light by the driving current Id of the driving transistor T2 during the fourth to sixth sections (4, 5, and 6).

During the seventh period (7), the black data (Vblack) is supplied to the data line (DL). The black data Vblack is supplied to the first node n1 via the switching transistor T1.

The drive transistor T2 is turned off by the black data Vblack, and the drive current Id is no longer generated.

During the eighth period (8), the black data Vblack is continuously supplied to the data line DL. Accordingly, when the charge of the second node n2 is exhausted to the organic light emitting diode OLED, the second node n2 becomes close to the second power voltage VSS, and the light emission of the organic light emitting diode OLED Since the black data Vblack is supplied to the gate terminal of the driving transistor T2, that is, the second node n2, the threshold voltage of the driving transistor T2 shifted during the light emitting period is set to the original threshold voltage Will be restored.

The black data Vblack may have a negative polarity that is at least larger than the potential difference between 0V and the maximum data voltage having a positive polarity and capable of expressing the maximum gradation when 0V is used as a reference. For example, when the maximum data voltage is 5V, the black data (Vblack) may be -6V or less.

As the black data Vblack is lowered, the shifted threshold voltage of the driving transistor T2 can be quickly restored to the original threshold voltage.

Preferably, the black data Vblack may be a negative polarity (voltage) having a range of two to three times the maximum data voltage.

The organic light emitting diode OLED emits light during the third through sixth intervals ③, ④, ⑤ and ⑥ and the first and second sections ① and ② and the seventh and eighth sections 7, 8), the organic light emitting diode OLED may not emit light.

The pixel 42 on each gate line GL can be driven by such a driving method.

As described above, the first and second scan pulses Vsp1 and Vsp2 may be supplied to the respective gate lines GL with a time interval therebetween. The organic light emitting diode OLED emits light when the first scan pulse Vsp1 is supplied and the organic light emitting diode OLED emits no light when the second scan pulse Vsp2 is supplied.

For example, it is assumed that the first to tenth gate lines are present.

The first scan line Vsp1 is supplied to the first gate line and the organic light emitting diode OLED of each pixel on the first gate line emits light.

In this order, the first scan pulse Vsp1 is sequentially supplied to the second to tenth gate lines, and the organic light emitting diode OLED of each pixel on each gate line can emit light.

On the other hand, after the organic light emitting diode OLED of each pixel on the fourth gate line is emitted, the second scan pulse Vsp2 is supplied to the first gate line, and the organic light emitting diode (OLED) is not emitted.

Next, after the organic light emitting diode OLED of each pixel on the fifth gate line is emitted, the second scan pulse Vsp2 is supplied to the second gate line, and the organic light emitting diode of each pixel on the second gate line, (OLED) is not emitted.

With such a driving method, the organic light emitting diode OLED of each pixel on the first to tenth gate lines emits light and then is not emitted.

FIG. 4 is a diagram for explaining a driving method of the organic light emitting display device.

As shown in FIG. 4, the organic light emitting diode OLED of each pixel on each gate line is not emitted after a predetermined time elapses after the light is emitted .

Accordingly, the organic light emitting diodes OLED of the respective pixels on the respective gate lines are sequentially emitted during one frame, while the organic light emitting diodes of the respective pixels on the gate lines spaced apart from the current gate line by a predetermined distance are not emitted.

As described above, the organic light emitting diodes OLED of the respective pixels on the respective gate lines sequentially emit light, and the organic light emitting diodes of the respective pixels on the respective gate lines are not sequentially emitted after a predetermined time elapses.

FIG. 5 is a diagram showing voltage changes at the first and second nodes of the organic light emitting diode display of the present invention.

As shown in Fig. 5, when the first power voltage Vpower is transitioned from the high level VDH to the low level VDL, the second node n2 is turned on at the low level of the first power voltage Vpower VDL, and the voltage of the first node n1 is also lowered due to the influence of the second node n2.

When the first scan pulse Vsp1 is supplied, the first node n1 is restored to the original voltage and the second node n2 is turned on when the first power voltage Vpower changes from the low level VDL to the high level VDH). ≪ / RTI >

When the data signal (for example, the data voltage Vdn) is supplied, the first node n1 is charged with the data voltage Vdn and the second node n2 is further increased and saturated.

6 is a graph showing a change in driving current according to a voltage deviation of a threshold voltage of a driving transistor in the organic light emitting display according to the present invention.

As shown in FIG. 6, in the OLED display according to the present invention, the driving current is hardly changed despite the voltage deviation of the threshold voltage of the driving transistor.

7 is a graph for explaining the restoration of the deterioration of the driving transistor of the organic light emitting diode display of the present invention.

The threshold voltage can be shifted in the positive direction by the stress in the (+) direction of the driving transistor by the data voltage Vdn.

In this case, stress in the (-) direction is applied by the black data Vblack supplied to the driving transistor, so that the threshold voltage can be shifted in the negative direction and restored to the original threshold voltage.

1 is a view illustrating an organic light emitting diode display according to the present invention.

2 is a circuit diagram showing the pixel of Fig.

3 is a waveform diagram showing waveforms for driving the organic light emitting diode display of the present invention.

FIG. 4 is a diagram for explaining a driving method of the organic light emitting display device.

FIG. 5 is a diagram showing voltage changes at the first and second nodes of the organic light emitting diode display of the present invention.

6 is a graph showing a change in driving current according to a voltage deviation of a threshold voltage of a driving transistor in the organic light emitting display according to the present invention.

7 is a graph for explaining the restoration of the deterioration of the driving transistor of the organic light emitting diode display of the present invention.

Description of the Related Art

10: gate driver 20: data driver

30: voltage supply unit 40: organic light emitting display panel

42: pixel

Claims (6)

A switching transistor coupled between the data line and the first node and having a gate terminal coupled to the gate line, and a second transistor coupled between the voltage supply line and the second node, A driving transistor connected to the first node, a storage capacitor connected between the first and second nodes, and an organic light emitting diode connected to the second node, A first step of charging a second node with a low-level power voltage supplied to the voltage supply line; The switching transistor is turned on by the first scan pulse supplied to the gate line and the black data supplied to the data line is charged to the first node via the switching transistor while the high voltage supplied to the voltage supply line Level power voltage is supplied to the driving transistor, and charging the storage capacitor with a threshold voltage of the driving transistor; A third step of supplying a data voltage supplied to the data line to the driving transistor via the switching transistor; And And a fourth step of emitting the organic light emitting diode by a driving current generated by the driving transistor, Wherein the driving current is determined by the data voltage and the black data. The method of claim 1, wherein the black data is at least higher than a low level of the power voltage. 2. The method of claim 1, wherein the black data is a negative voltage having a range of 2 to 3 times the maximum data voltage capable of representing the maximum gray level. The method of claim 1, further comprising: a fifth step of charging the first node via the switching transistor with black data supplied to the data line when the switching transistor is turned on by a second scan pulse supplied to the gate line; And And a sixth step of turning off the driving transistor by the black data and stopping the light emission of the organic light emitting diode. 5. The method of claim 4, wherein the threshold voltage of the driving transistor that is driven by the data voltage is restored by the black data. 5. The method of claim 4, wherein each of the first and second scan pulses has a half width of one horizontal period.

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