KR20150071731A - Organic light emitting display device - Google Patents

Abstract

Provided in the present invention is an organic light emitting display device which comprises a display panel defining pixels upon crossing data line and gate line; a gate driving part supplying a scan signal to the gate line; and a data driving line supplying data voltage to pixels through the data line, and supplying black data voltage to at least one pixel in which threshold voltage of a driving transistor is displaced from present range.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to an organic light-

TECHNICAL FIELD [0001] The present invention relates to a technique for improving a pixel defect of an organic light emitting display.

2. Description of the Related Art In recent years, an organic light emitting diode (OLED) display device that has been spotlighted as a display device has advantages of high response speed, high luminous efficiency, high luminance and wide viewing angle by using an organic light emitting diode (OLED)

Such an organic light emitting display device arranges pixels including organic light emitting diodes in a matrix form and controls the brightness of pixels selected by a scan signal according to data gradation.

In addition to the organic light emitting diode, each pixel of the organic light emitting display includes a data line and a gate line intersecting with each other, and a transistor and a storage capacitor having a connection structure.

Among the transistors included in each pixel of the organic light emitting diode display device, a driving transistor for driving the organic light emitting diode is included, and the driving transistor has a threshold voltage as an intrinsic characteristic value.

The threshold voltage of the driving transistor DT may vary as the driving time becomes longer. In this case, the luminance of the pixel is not determined to be a desired value and the image quality is degraded.

Accordingly, a technique has been developed in which the threshold voltage of the driving transistor is compensated by sensing the threshold voltage of the driving transistor of each pixel.

However, such a conventional threshold voltage compensation technique has a problem within a certain range. That is, when the threshold voltage of the driving transistor becomes larger than a specific value or becomes smaller than a specific value, there is a limit that the changed threshold voltage can not be compensated.

Therefore, even if a conventional threshold voltage compensation technique is applied, a pixel out of the compensation range continues to serve as a factor of deteriorating the image quality. Particularly, when the threshold voltage is changed and the pixel is brightly lit, the user's visibility to the luminescent spot is high, so that the picture quality becomes worse. However, the related art can not solve such a problem.

In view of the foregoing, an object of the present invention is to provide a technique for lowering the visibility of a defective pixel by igniting a corresponding pixel when the threshold voltage of the driving transistor deviates from the compensation range.

In another aspect, a threshold voltage of a driving transistor may be recovered to within a compensation range after being out of a compensation range. An object of the present invention is to temporarily store a pixel whose threshold voltage of the driving transistor is out of the compensation range, And when the pixel is recovered within the compensation range, it provides a technique of performing normal driving again.

According to one aspect of the present invention, there is provided a display device including a display panel in which pixels are defined along an intersection of a data line and a gate line, a gate driver for supplying a scan signal to the gate line, And a data driver for supplying a data voltage to the pixels and supplying a black data voltage to at least one pixel whose threshold voltage of the driving transistor is out of a preset range.

As described above, according to the present invention, when the threshold voltage of the driving transistor deviates from the compensation range on one side, there is an effect that the visibility of the defective pixel is lowered by darkening the pixel. According to the present invention, on the other side, when a pixel whose threshold voltage of the driving transistor deviates from the compensation range is temporarily cradled, the pixel can be normally driven again when it is restored within the compensation range.

1 is a schematic diagram of an organic light emitting diode display 100 according to an embodiment.
2 is an equivalent circuit diagram of one pixel P of the OLED display 100 of FIG.
3 and 4 are views showing a threshold voltage transfer phenomenon in which the threshold voltage Vth of the driving transistor DT is increased or decreased with the driving time.
5 is a view for explaining that the organic light emitting diode display 100 according to an embodiment darkens a pixel out of the compensation range.
FIG. 6 is a flowchart of a first exemplary method in which the organic light emitting diode display 100 according to the embodiment darkens a pixel out of the compensation range.
7 is a diagram showing an organic light emitting diode display 100 according to an embodiment including a red pixel R, a white pixel W, a green pixel G and a blue pixel B.
FIG. 8 is a flowchart of a second exemplary method in which the organic light emitting diode display 100 according to an embodiment darkens a pixel out of the compensation range.
9 is a diagram showing that the threshold voltage of the driving transistor DT is recovered to the normal range according to the driving time.
10 is a flowchart of a third exemplary method in which the organic light emitting diode display 100 according to an embodiment darkens a pixel out of the compensation range.
11 is a diagram for explaining a state in which the threshold voltage of the driving transistor DT is not dark-ignited to the black data voltage.
12 is a flowchart of a fourth exemplary method in which the organic light emitting diode display 100 according to an embodiment darkens a pixel out of the compensation range.
13 is a diagram showing a pixel to which the fourth exemplary method is applied and a waveform of the pixel.
FIG. 14 is a diagram for explaining an embodiment in which a reference voltage is supplied to pixels receiving a reference voltage through a common line.
FIG. 15 is a flowchart of a fifth exemplary method in which the organic light emitting diode display 100 according to an embodiment darkens a pixel out of the compensation range.

Some embodiments of the present invention will now be described in detail with reference to exemplary drawings. It should be noted that, in adding reference numerals to the constituent elements of the drawings, the same constituent elements are denoted by the same reference numerals even though they are shown in different drawings. In the following description of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather unclear.

In describing the components of the present invention, terms such as first, second, A, B, (a), and (b) may be used. These terms are intended to distinguish the constituent elements from other constituent elements, and the terms do not limit the nature, order or order of the constituent elements. When a component is described as being "connected", "coupled", or "connected" to another component, the component may be directly connected to or connected to the other component, It should be understood that an element may be "connected," "coupled," or "connected."

1 is a schematic diagram of an organic light emitting diode display 100 according to an embodiment.

1, an OLED display 100 according to an embodiment includes a display panel 110, a data driver 120, a gate driver 130, a sense driver 140, a timing controller 150, A reference voltage supply unit 160, and the like.

The display panel 110 is formed with the data lines DL (1) to DL (n) and the gate lines GL (1) to GL n) and a plurality of pixels (P) are defined according to intersections of the gate lines GL (1) to GL (m).

The data driver 120 supplies the data voltages to the data lines DL (1) to DL (n).

The gate driver 130 sequentially supplies scan signals to the gate lines GL (1) to GL (m).

The display panel 110 also includes sense lines SL (1) to SL (m) and reference voltage lines RVL (1) to RVL (l).

The sense driver 140 sequentially supplies a sense signal to the sense lines SL (1) to SL (m).

The reference voltage supply unit 160 supplies the reference voltage to the reference voltage lines RVL (1) to RVL (I).

The timing controller 150 controls the driving timings of the data driver 120, the gate driver 130, the sense driver 140, and the reference voltage supplier 160, and outputs various control signals.

The gate driving unit 130 and the sense driving unit 140 may be separately implemented, and in some cases, they may be included in one gate driving unit.

1, the gate driver 130 may be located on only one side of the display panel 110, or may be located on both sides of the display panel 110 divided into two, as shown in FIG. The same applies to the sense driver 140.

The gate driving unit 130 and the sense driving unit 140 may include a plurality of gate driving integrated circuits such as a Tape Automated Bonding (TAB) The display panel 110 may be connected to a bonding pad of the display panel 110 in a COG method or may be implemented in a GIP (Gate In Panel) type and directly formed on the display panel 110.

The data driver 120 and the reference voltage supplier 160 may be separately provided or may be included in one data driver.

In addition, the data driver 120 may include a plurality of data driver ICs (also referred to as source driver ICs), which may be a tape automated bonding (TAB) May be connected to a bonding pad of the display panel 110 in a chip on glass (COG) method, or may be implemented in a GIP (Gate In Panel) type and directly formed on the display panel 110.

Each pixel P is connected to a data line DL, a gate line GL, a sense line SL and a reference voltage line RVL. Will be described in detail.

2 is an equivalent circuit diagram of one pixel P of the OLED display 100 of FIG.

Referring to FIG. 2, a pixel P of the organic light emitting diode display 100 includes an organic light emitting diode (OLED) and a driving circuit for driving the organic light emitting diode OLED.

2, the driving circuit unit for driving the organic light emitting diode OLED in each pixel P includes a driving transistor DT for supplying a current to the organic light emitting diode OLED, Which controls the turn-on or turn-off of the driving transistor DT by controlling the data voltage to be applied to the first node N1 of the driving transistor DT, And a storage capacitor Cstg for maintaining a data voltage applied to the first node N1 of the driving transistor DT for one frame. The driving transistor DT includes a first transistor T1, And a second transistor T2 as a sensing transistor for sensing a threshold voltage (Vth) of the first transistor T2.

The connection structure of the three transistors DT, T1, and T2 and one capacitor Cstg will be described with reference to FIG.

The driving transistor DT may be an N-type transistor or a P-type transistor. 2A is an equivalent circuit for one pixel P in the case where the driving transistor DT is N type and FIG. 2B is an equivalent circuit in the case where the driving transistor DT is P type And is an equivalent circuit for the pixel P.

First, referring to FIG. 2A, the driving transistor DT has three nodes N1, N2 and N3 as a transistor for driving the organic light emitting diode OLED. The first node N1 of the driving transistor DT is connected to the first transistor T1 and the second node N2 is connected to the anode of the organic light emitting diode OLED, Is connected to a driving voltage line (DVL) to which a driving voltage VDD is supplied.

The first transistor T1 is controlled by the scan signal SCAN supplied from the gate line GL and is connected between the data line DL and the first node N1 of the driving transistor DT, (Vdata) supplied from the data line DL to the first node N1 of the driving transistor DT.

The second transistor T2 is controlled by a sense signal SENSE supplied from a sense line SL and a reference voltage line RVL to which a reference voltage Vref is supplied, Lt; RTI ID = 0.0 > DT). ≪ / RTI >

The storage capacitor Cstg is connected between the first node N1 and the second node N2 of the driving transistor DT.

2 (b), the driving transistor DT has three nodes N1, N2 and N3 as transistors for driving the organic light emitting diode OLED. The first node N1 of the driving transistor DT is connected to the first transistor T1 and the second node N2 is connected to the anode of the organic light emitting diode OLED, Is connected to a driving voltage line (DVL) to which a driving voltage VDD is supplied.

The first transistor T1 is controlled by the scan signal SCAN supplied from the gate line GL and is connected between the data line DL and the first node N1 of the driving transistor DT, (Vdata) supplied from the data line DL to the first node N1 of the driving transistor DT.

The second transistor T2 is controlled by the sense signal SENSE supplied from the sense line SL and is connected between the reference voltage line RVL and the second node N2 of the driving transistor DT . At this time, the reference voltage is not supplied to the reference voltage line RVL, and only the threshold voltage of the driving transistor DT through the voltage sensing of the second node N2 may be sensed.

The storage capacitor Cstg is connected between the first node N1 and the third node N3 of the driving transistor DT.

When the driving transistor DT is an N-type transistor, the first node N1 is a gate node, the second node N2 is a source node, and the third node N3 is a gate node And may be a drain node. When the driving transistor DT1 is a P-type transistor, the first node N1 is a gate node, the second node N2 is a drain node, and the third node N3 is a drain node. And may be a source node.

In the drawings and the description according to the embodiment, for convenience of explanation, not only the driving transistor DT but also the first transistor T1 and the second transistor T2 connected thereto are exemplified by N-type transistors, The first node N1 of the driving transistor DT is a gate node and the second node N2 is a source node and the third node N3 is a drain node, .

On the other hand, the driving transistor DT of each pixel has a threshold voltage as an intrinsic characteristic value, and the threshold voltage of the driving transistor DT may change as the driving time increases. This may prevent the luminance of the corresponding pixel from becoming a desired level, or may cause a luminance difference between the pixels, thereby deteriorating the image quality.

Therefore, when the threshold voltage of the driving transistor DT of each pixel is sensed and there is a threshold voltage deviation between the pixels or when the threshold voltage of each pixel is different from the reference threshold voltage, the threshold voltage of the driving transistor DT To maintain the desired level of brightness.

However, the compensation of the threshold voltage of the driving transistor DT has a compensation limit within a certain range. That is, when the threshold voltage of the driving transistor DT becomes larger than a specific value or becomes smaller than a specific value, the changed threshold voltage can not be compensated.

Therefore, when the threshold voltage of the driving transistor DT is changed over a predetermined range, that is, when the threshold voltage moves and deviates from the predetermined range, the threshold voltage compensation is impossible and the image quality is degraded.

3 and 4 are views showing a threshold voltage transfer phenomenon in which the threshold voltage Vth of the driving transistor DT increases or decreases with the driving time.

4, a description will be given of the threshold voltage shift phenomenon in the (+) direction in which the threshold voltage of the driving transistor DT increases with the driving time. Referring to FIG. 4, The threshold voltage shift phenomenon in the (-) direction in which the threshold voltage decreases with the driving time will be described.

Prior to the description below, we first summarize some terms.

(+) Direction means a direction in which a threshold voltage increases, and "(-) direction" means a direction in which a threshold voltage decreases in relation to a direction in which a threshold voltage varies.

Further, "threshold voltage shift (Vth Shift)" means that the threshold voltage is increased or decreased. The phenomenon in which the threshold voltage shift occurs in the positive direction is referred to as (+) threshold voltage shift, and the phenomenon in which the threshold voltage shift occurs in the negative (-) direction is referred to as (-) threshold voltage shift.

The range of the threshold voltage that can compensate the threshold voltage is called the "threshold voltage compensation range ". The threshold voltage compensation range has an upper limit value and a lower limit value. The upper limit value of the threshold voltage compensation range is referred to as a "threshold voltage compensation limit (+)" and the lower limit value of the threshold voltage compensation range is referred to as a " .

The threshold voltage compensation range may be a substantial range in which the OLED display 100 can compensate for the threshold voltage and may be a predetermined range that is wider or narrower than the actual range for efficient recovery driving.

FIG. 3 is a diagram showing the phenomenon of (+) threshold voltage shift of the driving transistor DT in the pixel of the organic light emitting diode display 100 and the luminance quality deterioration thereof.

3 (a) is a graph showing that the threshold voltage of the driving transistor DT changes as the driving time of the driving transistor DT increases. Referring to FIG. 3, the threshold voltage of the driving transistor DT is .

That is, a "(+) threshold voltage shift phenomenon" in which the threshold voltage of the driving transistor DT becomes larger as the driving time of the driving transistor DT becomes longer is exhibited.

In addition, the threshold voltage of the driving transistor DT becomes larger within the "threshold voltage compensation range" during a certain period (0 to T1) during which the driving time increases. Therefore, during this period (0 to T1), the threshold voltage of the driving transistor DT is compensated for at a desired level (the level at which the deviation from the threshold voltage of the driving transistor of the other pixel is eliminated or reduced or the reference threshold voltage becomes a level) I can do it.

However, the threshold voltage of the driving transistor DT starts to increase beyond the threshold voltage compensation range when passing the interval (0 to T1), that is, at the time T1, and the threshold voltage of the driving transistor DT Can not be compensated to the desired level.

3B shows how the luminance of the pixel changes when the threshold voltage of the driving transistor DT changes as shown in Fig. 3 (a) as the driving time of the driving transistor DT increases. Graph.

3 (b), the threshold voltage of the driving transistor DT is increased within the threshold voltage compensation range until the driving time of the driving transistor DT reaches the time T1, The voltage can be compensated. Accordingly, the luminance of the pixel can be maintained at a desired level (L1) until the driving time of the driving transistor DT reaches the time T1.

However, as the driving time of the driving transistor DT passes the time T1, the threshold voltage of the driving transistor DT starts to increase beyond the threshold voltage compensation range. That is, the threshold voltage of the driving transistor DT starts to become larger than the threshold voltage compensation threshold value (+) which is the upper limit value of the threshold voltage compensation range.

From this time point, that is, after the time point T1, the threshold voltage of the driving transistor DT can not be compensated to a desired level. Accordingly, the amount of current supplied to the organic light emitting diode (OLED) by the driving transistor DT is gradually reduced from the desired amount, and the luminance of the pixel is maintained at the desired level (L1) It gradually falls.

4 is a graph showing the (-) threshold voltage transfer phenomenon of the driving transistor DT in the pixel of the OLED display 100 and the luminance quality deterioration thereof.

4A is a graph showing that the threshold voltage of the driving transistor DT changes as the driving time of the driving transistor DT increases. Referring to FIG. 4A, the threshold voltage of the driving transistor DT is a driving time As shown in Fig.

That is, a "(-) threshold voltage transfer phenomenon" in which the threshold voltage of the driving transistor DT becomes smaller as the driving time of the driving transistor DT becomes longer is exhibited.

In addition, the threshold voltage of the driving transistor DT is reduced within the "threshold voltage compensation range" during a certain period (0 to T2) during which the driving time increases. Therefore, during this period (0 to T2), the threshold voltage of the driving transistor DT is compensated for at a desired level (a level at which the deviation from the threshold voltage of the driving transistor of the other pixel is eliminated or decreased or a reference threshold voltage becomes) I can do it.

The threshold voltage of the driving transistor DT starts to become smaller than the threshold voltage compensation range and the threshold voltage of the driving transistor DT starts decreasing from this point. The voltage can not be compensated to the desired level.

4B shows how the luminance of the pixel changes when the threshold voltage of the driving transistor DT changes as shown in Fig. 4A as the driving time of the driving transistor DT increases. Fig. Graph.

Referring to FIG. 4B, the threshold voltage of the driving transistor DT is reduced within the threshold voltage compensation range until the driving time of the driving transistor DT reaches the time T2, The threshold voltage can be compensated. Accordingly, the luminance of the pixel can be maintained at a desired level (L2) in the pixel until the driving time of the driving transistor DT reaches the time T2.

However, as the driving time of the driving transistor DT passes the time T2, the threshold voltage of the driving transistor DT starts to become smaller than the threshold voltage compensation range. That is, the threshold voltage of the driving transistor DT starts to become smaller than the threshold voltage compensation threshold value (-) which is the lower limit of the threshold voltage compensation range.

From this time point, that is, after the time point T2, the threshold voltage of the driving transistor DT can not be compensated to a desired level. Accordingly, the amount of current supplied to the organic light emitting diode (OLED) by the driving transistor DT increases more than the desired amount of current, and in an abnormal state in which the luminance of the pixel can not be maintained at a desired level (L2) It becomes higher and higher. If such a state continues to progress, the corresponding pixel is burned. The fact that the pixel is brightly lit means that the threshold voltage of the driving transistor DT is too low to always exhibit a high gradation even with the data voltage inputted to express a low gray level.

Since the bright point is higher in visibility than the dark point, the phenomenon of luminance blur in these pixels is a main factor for deteriorating the image quality. Accordingly, it is a method to improve the image quality by darkening the bright spot in a state where the normal luminance can not be exerted beyond the compensation range.

One embodiment provides a technique for darkening a pixel whose threshold voltage of the driving transistor DT is out of a predetermined range. In particular, one embodiment provides a technique of darkening a pixel by supplying a black data voltage to the driving transistor DT of a pixel whose threshold voltage is out of a predetermined range.

5 is a view for explaining that the organic light emitting diode display 100 according to an embodiment darkens a pixel out of the compensation range.

As shown in FIG. 5, each pixel includes an organic light emitting diode (OLED), a driving transistor DT for supplying current to the organic light emitting diode OLED to drive the organic light emitting diode OLED, The driving transistor DT is controlled to turn on or turn off by controlling the data voltage Vdata to be applied to the first node N1 of the driving transistor DT, A first transistor T1 serving as a switching transistor for controlling the data voltage Vdata applied to the first node N1 of the driving transistor DT and a storage capacitor And a sensing transistor for sensing the threshold voltage of the driving transistor DT by applying a reference voltage Vref to the second node of the driving transistor DT and being controlled by the sense signal SENSE, DT2) All.

5, in order to sense the threshold voltage of the driving transistor DT, the first transistor T1 is turned on by the scan signal SCAN, and the data driver 120 of the corresponding pixel The supplied data voltage Vdata is applied to the first node N1 of the driving transistor DT through the data line DL.

At this time, the second transistor T2 is turned on by the sense signal SENSE, and the reference voltage Vref supplied from the reference voltage supply unit 160 is applied to the second electrode of the driving transistor DT through the reference voltage line RVL. And is applied to the node N2.

That is, a constant voltage is applied to each of the first node N1 and the second node N2 of the driving transistor DT, so that a constant potential difference Vdata-N2 is applied to both ends N1 and N2 of the storage capacitor Cstg, Vref is generated, and the storage capacitor Cstg is charged with a charge corresponding to a constant potential difference (Vdata-Vref).

Thereafter, a switch (not shown) connected to the reference voltage line RVL is turned off and connected to an ADC (Analog Digital Converter) for threshold voltage sensing. The ADC may be included in the same package as the reference voltage supply unit 160 in hardware. In the embodiment of FIG. 5, the ADC is shown to be included in the reference voltage supplier 160, and the following description will be made with reference to the embodiment of FIG. 5 for convenience of explanation. And may be configured separately from the reference voltage supply unit 160.

The process of sensing the threshold voltage of the driving transistor DT at the second node N2 by the ADC will be described in further detail.

When the supply of the reference voltage to the reference voltage line RVL is terminated and the reference voltage line RVL is connected to an ADC (Analog Digital Converter) for threshold voltage sensing, the second node N2 of the driving transistor DT The applied constant voltage Vref disappears and the voltage of the second node N2 of the driving transistor DT floats.

The constant voltage Vdata is still applied to the first node N1 of the driving transistor DT but the constant voltage is not applied to the second node N2 so that the second node N2 of the driving transistor DT ) Is increased.

The voltage of the second node N2 of the driving transistor DT rises until the potential difference between the first node N1 and the second node N2 becomes the threshold voltage of the driving transistor DT.

At this time, the ADC measures the voltage (Vdata-Vth) of the second node N2 of the driving transistor DT and senses the threshold voltage of the driving transistor DT. Since the data voltage Vdata is a known value in advance, the threshold voltage Vth can be obtained by subtracting the voltage (Vdata-Vth) measured from the already known data voltage (Vdata).

According to the threshold voltage sensing method, the sensed threshold voltage can be stored in a memory (not shown) and used for threshold voltage compensation.

Regarding the threshold voltage compensation, the timing controller 150 receives the digital value of the threshold voltage (Vth) obtained from the ADC, calculates a compensation value for threshold voltage compensation using the received digital value, (Vdata '= Vdata + Vth) to the data driver 120 of the corresponding pixel.

Accordingly, the data driver 120 converts the data voltage Vdata into the changed data voltage Vdata '= Vdata + Vth according to the compensation value calculated by the timing controller 150, Or outputs the changed data voltage (Vdata '= Vdata + Vth) transmitted from the timing controller 150 to the data line DL in analog form. Thus, the threshold voltage of the driving transistor DT of the pixel is compensated.

In the threshold voltage sensing and compensation process described above, the threshold voltage of the driving transistor DT of all the pixels in the display panel 110 or a conversion value for recognizing the threshold voltage is stored in the memory. Then, at the next sensing, Or a process of updating the conversion value.

On the other hand, in one embodiment, when the threshold voltage of the driving transistor DT of all the pixels is sensed according to the threshold voltage sensing and compensation process as described above, the threshold voltage of the driving transistor DT A pixel out of the threshold voltage compensation range is confirmed, that is, a pixel subjected to a threshold voltage shift outside the threshold voltage compensation range is confirmed, and a black data voltage is supplied to the identified pixel. When the black data voltage is supplied to the pixel whose threshold voltage is out of the threshold voltage compensation range, the pixel is darkened.

FIG. 6 is a flowchart of a first exemplary method in which the organic light emitting diode display 100 according to the embodiment darkens a pixel out of the compensation range.

Referring to FIG. 6, the OLED display 100 senses a threshold voltage of each pixel driving transistor DT in the display panel 110 (S602). The threshold voltage of the pixel driving transistor DT can be sensed by measuring the voltage of the second node N2 as in the embodiment of FIG. At this time, the sensing voltage of the second node N2 may be performed by the ADC included in the reference voltage supplier 160, and the sensed threshold voltage may be transmitted to the timing controller 150. [

For each pixel, the OLED display 100 checks whether the sensed threshold voltage is within a preset range (S604). At this time, the organic light emitting diode display 100 can set the predetermined range to a range equal to or lower than the lower limit value of the threshold voltage compensation range of the driving transistor DT. When the threshold voltage of the driving transistor DT becomes smaller than the lower limit value of the threshold voltage compensation range, the pixel is likely to be ignited, so that the OLED display 100 can ignite such a pixel.

If the threshold voltage of the driving transistor DT of the pixel is smaller than the lower limit value of the threshold voltage compensation range in step S604 (YES in step S604), the OLED display 100 can supply the black data voltage to the pixel S606). The black data voltage is a data voltage for darkening the pixel. Such a data voltage may have a value of about 0.5 V as a data voltage for causing the pixel to express a gray level value of 0, but it is not limited to a specific value.

If the threshold voltage of the driving transistor DT of the pixel is equal to or greater than the lower limit value of the threshold voltage compensation range (NO in S604) in step S604, the OLED display 100 can supply the normal data voltage to the corresponding pixel (S608 ). Here, the normal data voltage refers to a data voltage in other cases except for the case where the black data voltage is intentionally supplied for ignition of the arm, and is a data voltage corresponding to an image to be implemented through the corresponding pixel.

In the exemplary method of FIG. 6, the organic light emitting diode display 100 determines the threshold voltage of each pixel and supplies a black data voltage or a normal data voltage to the pixel. However, The determination may be performed by the timing controller 150, and supplying the black data voltage or the normal data voltage may be performed by the data driver 120.

Meanwhile, the organic light emitting diode display 100 can selectively apply the ignition according to the color of the pixel.

7 is a diagram showing an organic light emitting diode display 100 according to an embodiment including a red pixel R, a white pixel W, a green pixel G and a blue pixel B.

Referring to FIG. 7A, the OLED display 100 includes a red pixel R, a white pixel W, a green pixel G, and a blue pixel B, A point 710 for the image on the display panel 110 can be displayed by a combination of R, W, G, One point 710 is referred to as a pixel of an image, and each of the color pixels R, W, G, and B included in the pixel may be represented by a sub-pixel. However, in the present invention, We do not use the term sub-pixel for harmonization.

The red pixel R, the white pixel W, the green pixel G and the blue pixel B may have the same structure as the embodiment shown in Fig. 2 on an equivalent circuit. However, the physical properties of the organic light emitting diode (OLED) are different for each pixel, so that different light is emitted. Although the organic light emitting diode display 100 includes the pixels R, W, G, and B of the four colors in FIG. 7A, the OLED display 100 may include three colors Only the pixels R, G, and B may be included. Further, the organic light emitting diode display 100 may display a point of the image by combining colors other than the above-described colors (for example, red pixel (R), yellow pixel (Yellow) and blue pixel (B) It is possible.

The OLED display 100 may darken a pixel of a pixel whose threshold voltage of the driving transistor DT is out of a preset range among the pixels, depending on the embodiment. In the OLED display 100, The red pixel R or the white pixel W having a high visibility when illuminated is illuminated with a dark color (for example, the black data voltage is supplied to the red pixel R or the white pixel W) (For example, a green pixel G or a blue pixel B) may not be dark-ignited (e.g., can supply a normal data voltage).

As another embodiment of the dark ignition according to the color of the pixel, when the OLED display 100 darkens the white pixel W (for example, when supplying the black data voltage with the white pixel W) The organic light emitting diode display 100 may supply the data voltage adjusted to the display pixel 710 so that only one red pixel R, green pixel G and blue pixel B are displayed.

7B is a diagram showing that only the red pixel R, the green pixel G and the blue pixel B operate normally at one point 710 while the white pixel W is darkened. The OLED display 100 displays a point of the image using only the red pixel R, the green pixel G and the blue pixel B because all the light can be expressed by a combination of red, green and blue can do. 7 (a), the organic light emitting diode display 100 emits light corresponding to the white pixel W in FIG. 7 (a) to other pixels in FIG. 7 (b) (R, G, B). Therefore, a data voltage adjusted to emit light of a higher gradation than the existing (case of (a) in Fig. 7) is supplied to each pixel for the red pixel R, the green pixel G and the blue pixel B do.

FIG. 8 is a flowchart of a second exemplary method in which the organic light emitting diode display 100 according to an embodiment darkens a pixel out of the compensation range. The second exemplary method corresponds to the embodiment described with reference to FIG. 7 (b).

8, the OLED display 100 displays data corresponding to a red pixel R, a white pixel W, a green pixel G, and a blue pixel B for displaying respective points of an image, (S802). The OLED display 100 may further include a host (not shown), which may be an external video source device such as a navigation system, a set top box, a DVD player, a Blu-ray player, PC, a home theater system, a broadcast receiver, a phone system, etc., and receive data from the external video source device. The host (not shown) may convert the data from the external video source device into a format suitable for display on the display panel 110, including a system on chip (SoC) including a scaler. The host (not shown) transfers this data to the timing controller 150.

The OLED display 100 senses the threshold voltage of the white pixel W of the display panel 110 (see the embodiment of FIG. 5 for the threshold voltage sensing) Is compared with the lower limit value of the threshold voltage compensation range (S804).

When the threshold voltage of the white pixel W is equal to or more than the lower limit value (NO in step S804), the organic light emitting diode display 100 displays the red pixel R, the white pixel W, the green pixel G, and the blue pixel B The data voltage corresponding to the data acquired in step S802 is supplied. The OLED display 100 includes a red pixel R, a white pixel W, a green pixel G and a blue pixel B in order to display a point of an image displayed on the display panel 110. [ .

When the threshold voltage of the white pixel W is smaller than the lower limit value (YES in S804), the organic light emitting diode display 100 displays one point of the image with only the red pixel R, the green pixel G and the blue pixel B The data corresponding to the three RGB pixels are adjusted for display (S808).

The organic light emitting diode display 100 supplies the black data voltage to the white pixel W to darken the white pixel W and supplies the black data voltage to the other pixels R, And supplies the adjusted data voltage.

On the other hand, there is a hardware cancer ignition method as a method of darkening a pixel. This hardware ignition method is a method of shutting off a power supply line to a pixel to be ignited. In this case, there is no way that the pixel is permanently darkened and can be restored normally.

In contrast, the organic light emitting diode display 100 according to the embodiment of the present invention softly ignites a pixel to be a dark object. In other words, the organic light emitting diode display 100 does not physically damage the pixel but adjusts the data voltage supplied to the corresponding pixel to perform software ignition.

As described with reference to FIGS. 3 and 4, the threshold voltage of the driving transistor DT may be made smaller or larger according to the driving time, and the smaller or larger threshold voltage may be restored to the normal range again with the lapse of time. The organic light emitting diode display 100 according to an exemplary embodiment of the present invention does not physically damage a pixel to be fired and performs software ignition of the pixel. Therefore, when the pixel is restored to the normal range, There are advantages to be able to.

9 is a diagram showing that the threshold voltage of the driving transistor DT is recovered to the normal range according to the driving time.

9A, the threshold voltage of the driving transistor DT having a value larger than the lower limit value (for example, the lower limit value of the threshold voltage compensation range) at the beginning (0 time in FIG. 9) Becomes smaller than the lower limit value due to the voltage transfer phenomenon. The organic light emitting diode display 100 can ignite the pixels whose threshold voltage of the driving transistor DT is lower than the lower limit value.

9 (a), the threshold voltage of the driving transistor DT becomes smaller than the lower limit value according to the driving time, becomes larger than the lower limit value, and can be recovered to within the threshold voltage compensation range. The OLED display 100 can supply the normal data voltage without supplying the black data voltage to the pixel if the threshold voltage of the driving transistor DT is greater than the lower limit and enters the threshold voltage compensation range.

When the threshold voltage of the driving transistor DT becomes lower than the lower limit value at the first time point, the organic light emitting diode display 100 according to the embodiment performs the ignition process on the pixel and, at the second time point, (Again, the normal data is supplied to the corresponding pixel without supplying the black data voltage).

The threshold voltage of the driving transistor DT may increase in one direction as shown in FIG. 9A, but it can be repeatedly increased or decreased near the lower limit value. In this case, if it is determined whether the dark ignition process or the normal process is performed based only on the lower limit value, the system of the OLED display 100 may become unstable by repeatedly performing normal ignition of the pixel and then performing normal processing again.

In order to prevent such a problem, the organic light emitting diode display 100 may set a hysteresis region near the lower limit value as shown in FIG. 9 (b). For example, when a pixel which is darkened and then enters within a compensation range is located in a hysteresis region (P1), the OLED display 100 continuously supplies a black data voltage to the pixel to ignite the pixel . The organic light emitting diode display 100 can supply the normal data voltage to the pixel if the threshold voltage of the pixel becomes larger and becomes larger than the hysteresis region (P2).

10 is a flowchart of a third exemplary method in which the organic light emitting diode display 100 according to an embodiment darkens a pixel out of the compensation range. The third exemplary method corresponds to the embodiment described with reference to FIG. 9 (b).

Referring to FIG. 10, the OLED display 100 sets initial parameters. At this time, the organic light emitting diode display 100 sets the dark ignition flag to 0 (S1002). Here, the arm ignition flag is set to 1 in the arm ignited state with the flag indicating the arm ignition state, and set to 0 in the arm ignition state.

The organic light emitting diode display 100 senses the threshold voltage of the driving transistor DT with respect to one pixel (S1004).

If the threshold voltage of the pixel is smaller than the lower limit of the compensation range (YES in S1006), the OLED display 100 determines whether the threshold voltage of the pixel is lower than the lower limit of the compensation range The data voltage is supplied to darken the corresponding pixel (S1008).

After the pixel is darkened, the OLED display 100 sets a dark ignition flag for the pixel to 1 (S1010). The dark ignition flag can be managed differently for each pixel.

When the time of one frame has elapsed, the organic light emitting display 100 again senses the threshold voltage of the corresponding pixel (moves to step S1004), determines whether the threshold voltage is smaller than the lower limit of the compensation range (S1006) When the threshold voltage of the pixel is equal to or greater than the lower limit value of the compensation range (NO in S1006), it is determined whether the pixel is to be processed normally.

The organic light emitting diode display 100 uses a hysteresis region as described in FIG. 9 (b) in determining whether to process the pixel normally.

First, the organic light emitting diode display 100 checks whether the dark ignition flag is set to 1 (S1012). At this time, if the dark ignition flag is set to 1 (YES in S1012), the corresponding pixel is the dark-ignored pixel in the previous frame.

For the dark-lit pixel, the organic light emitting diode display 100 checks whether the threshold voltage of the pixel is larger than the hysteresis area (S1014). At this time, when the threshold voltage of the pixel is larger than the lower limit value but is still smaller than the hysteresis region (YES in S1014), the organic light emitting diode display 100 continuously supplies the black data voltage to the pixel to darken the pixel S1008), and the ignition flag is also set to 1 continuously.

On the contrary, if the threshold voltage of the pixel is higher than the lower limit and is equal to or higher than the hysteresis region (NO at S1014), the OLED display 100 supplies the normal data voltage to the corresponding pixel according to the normal process (S1016) , And the ignition flag is also set to zero.

In step S1012, if the dark ignition flag is set to 0 (NO in step S1012), the pixel is the pixel that has been normally processed in the previous frame. Therefore, the organic light emitting diode display 100 continuously supplies the normal data voltage to the corresponding pixel (S1016), and also holds the dark ignition flag at zero.

The threshold voltage of the driving transistor DT can be reduced below the lower limit value as described with reference to Figs. 9 to 10, and can be restored to the compensation range (normal range) again. However, conversely, the threshold voltage of the driving transistor DT becomes smaller, and a state in which the pixel can not be ignited can be reached only by supplying the black data voltage to the pixel.

11 is a diagram for explaining a state in which the threshold voltage of the driving transistor DT is not dark-ignited to the black data voltage.

Referring to FIG. 11A, the threshold voltage of the driving transistor DT may be smaller than the lower limit value of the compensation range as well as the lower limit of the black data, as the driving voltage continues to decrease with the driving time. The point corresponding to reference numeral P3 in Fig. 11A is a point where the threshold voltage Vth of the driving transistor becomes smaller than the gate-source voltage Vgs of the driving transistor DT when the black data voltage is supplied .

When the gate-source voltage Vgs is less than the threshold voltage Vth, the driving transistor DT does not supply the current to the pixel. The organic light emitting diode display 100 supplies a black data voltage (for example, 0.5 V) in which the gate-source voltage Vgs of the driving transistor DT becomes sufficiently smaller than the threshold voltage Vth, So that the corresponding pixel is ignited. However, when the gate-source voltage Vgs of the driving transistor DT formed by the black data voltage becomes larger than the threshold voltage Vth, the pixel is not completely ignited by the black data voltage.

Referring to FIG. 11B, the gate-source voltage Vgs of the driving transistor DT is controlled by a data voltage Vdata supplied to the first node N1 and a reference voltage Vdata supplied to the second node N2 Vref). The OLED display 100 supplies the black data voltage so that the gate-source voltage Vgs of the driving transistor DT becomes smaller than the threshold voltage Vth of the driving transistor DT, (Vth) is lower than the black data limit, the OLED display 100 can no longer ignite the pixel through the data voltage (Vdata).

The organic light emitting diode display 100 may darken the pixel by increasing the reference voltage in such a state (a state where the threshold voltage corresponds to P3).

Referring to FIG. 11 (b), the gate-source voltage Vgs of the driving transistor DT is formed by the data voltage Vdata and the reference voltage Vref. The OLED display 100 uses a method of lowering the data voltage Vdata in order to reduce the gate-source voltage Vgs of the driving transistor DT. In the embodiment described below, The display apparatus 100 explains a technique of making the gate-source voltage Vgs of the driving transistor DT smaller by raising the reference voltage Vref.

For example, in the above-described embodiment, the organic light emitting diode display 100 can use 3 V as a reference voltage in both the normal data voltage supply and the black data voltage supply. At this time, the organic light emitting diode display 100 can lower the gate-source voltage Vgs of the driving transistor DT to -2.5 V by using a black data voltage of 0.5 V. In the embodiment described below, The reference voltage is increased to 5V, thereby lowering the gate-source voltage (Vgs) of the driving transistor DT to -4.5V.

In the embodiment described below, an embodiment is described in which the gate-source voltage (Vgs) of the driving transistor DT is made smaller by raising the reference voltage. However, depending on the structure of the pixel, The gate-source voltage Vgs can be made smaller. For example, when the driving transistor DT is of the P type, the source voltage is formed to be higher than the gate voltage. In this case, by lowering the reference voltage connected to the source, the driving transistor DT gate- Can be made smaller.

12 is a flowchart of a fourth exemplary method in which the organic light emitting diode display 100 according to an embodiment darkens a pixel out of the compensation range. The fourth exemplary method includes the embodiment of raising the reference voltage Vref described with reference to FIG. 11 (b).

12, the organic light emitting diode display 100 senses the threshold voltage of the driving transistor DT (S1202) and determines whether the threshold voltage deviates from a predetermined range (for example, a lower limit value of the compensation range) (S1204).

When the threshold voltage of the driving transistor DT is within a preset range (for example, when the threshold voltage is equal to or lower than the lower limit) (NO in S1204), the OLED display 100 supplies a normal data voltage to the pixel (S1206).

On the contrary, when the threshold voltage of the driving transistor DT is within the preset range (for example, the threshold voltage is equal to or less than the lower limit value) (YES in S1204), the OLED display 100 displays the second node N2) (S1208), and supplies the black data voltage to the first node N1 (S1210).

13 is a diagram showing a pixel to which the fourth exemplary method is applied and a waveform of the pixel.

Referring to FIG. 13A, the first pixel 1322 and the second pixel 1324 have independent structures and each have a reference voltage line. In other words, the first pixel 1322 is supplied with the reference voltage from the first reference voltage line RVL (1), and the second pixel 1324 receives the reference voltage from the second reference voltage line RVL (2) It is supplied.

13B is a waveform diagram when the first pixel 1322 supplied with the black data voltage is controlled according to the fourth example method.

Referring to FIG. 13B, a scan signal SCAN (shown in FIG. 11B) is supplied to the first pixel 1322 in a cycle in which a sense signal SENSE (signal supplied to T2 in FIG. 11B) b) is supplied to T1.

The data voltage Vdata and the reference voltage Vref are supplied in accordance with the scan signal. At this time, the OLED display 100 may supply the black data voltage to the first node N1 of the first pixel 1322 and the increased reference voltage to the second node N2.

FIG. 14 is a diagram for explaining an embodiment in which a reference voltage is supplied to pixels receiving a reference voltage through a common line.

Referring to FIG. 14A, the first pixel 1322 and the second pixel 1324 have a structure in which a reference voltage is supplied through a common line RVL (1). At this time, if the organic light emitting display 100 supplies the increased reference voltage through the common line RVL (1) to the first pixel 1322 to which the black data voltage is supplied, the second pixel 1324 also This is influenced by the increased reference voltage. Accordingly, the OLED display 100 increases the data voltage by the voltage increment? Of the reference voltage to maintain the gate-source voltage Vgs of the driving transistor DT in the second pixel 1324, 2 pixels 1324 in the same manner as in the first embodiment. Here, the voltage increment? May be referred to as an offset voltage in the sense that it is increased by a certain amount, but the present invention is not limited thereto.

Referring to the waveform diagram of FIG. 14B, the OLED display 100 supplies a scan signal SCAN within a period in which a sense signal SENSE is supplied, and supplies a scan signal SCAN to a common line RVL (1) And supplies the reference voltage Vref increased by the voltage DELTA. The organic light emitting diode display 100 supplies the black data voltage for the first pixel 1322 and the compensated data compensated for the second pixel 1324 so that the data voltage is increased by the offset voltage? Voltage is supplied.

FIG. 15 is a flowchart of a fifth exemplary method in which the organic light emitting diode display 100 according to an embodiment darkens a pixel out of the compensation range. The fifth exemplary method includes the embodiment described with reference to Fig. 14, and the pixel structure shown in Fig. 14 (a) is applied in the following description.

15, the organic light emitting diode display 100 senses a threshold voltage with respect to the first pixel 1322 and the second pixel 1324 (S1502), and detects the first pixel 1322 and the second pixel 1324 (S1504). The threshold voltage of the driving transistor DT of the driving transistor DT is determined to be within a preset range.

If it is determined that the threshold voltage of the driving transistor DT of the first pixel 1322 and the second pixel 1324 is within a predetermined range (for example, the threshold voltage is equal to or greater than the lower limit value of the compensation range) NO in S1504), the organic light emitting diode display 100 supplies a normal data voltage to the first pixel 1322 and the second pixel 1324 (S1506).

Conversely, when the threshold voltage of the driving transistor DT of the first pixel 1322 of the first pixel 1322 and the second pixel 1324 is out of a predetermined range (for example, the threshold voltage is lower than the lower limit value of the compensation range (YES in S1504), the OLED display 100 supplies the reference voltage increased to the common line RVL (1) (S1508).

Then, the OLED display 100 generates a compensation voltage for the second pixel 1324 to compensate for the second pixel 1324 with respect to an increase in the reference voltage (S1510). The compensation voltage for the second pixel 1324 in terms of maintaining the driving transistor DT gate-source voltage Vgs at a constant value may be equal to the increment? Of the reference voltage.

The OLED display 100 supplies the black data voltage to the first pixel 1322 and the second pixel 1324 applies the compensation voltage to the second pixel 1324. [ And supplies the compensated data voltage (S1512).

In the above description, the embodiment has been described in which the pixel whose threshold voltage of the driving transistor DT is out of the predetermined range is darkened. The threshold voltage of the driving transistor DT can be changed according to the threshold voltage shift phenomenon. At this time, if the threshold voltage of the driving transistor DT deviates from the compensation range, the pixel is not appropriately controlled, which may cause a deterioration of image quality. Particularly, in the case where the pixel is brightly ignited, since the brightly-ignited pixel has high visibility, the image quality can be further deteriorated. The organic light emitting diode display 100 has the effect of preventing deterioration in image quality caused by igniting a pixel whose threshold voltage of the driving transistor DT is out of a predetermined range and causing the pixel to be ignited. In addition, the presence of pixels out of the compensation range means that there is an uncontrolled pixel, which means that predictability of image quality deteriorates. In the above-described embodiment, the OLED display 100 senses a threshold voltage, It is possible to realize predictable image quality by judging difficult pixels and maintaining such pixels in a constant state (dark ignition state).

It is to be understood that the terms "comprises", "comprising", or "having" as used in the foregoing description mean that the constituent element can be implanted unless specifically stated to the contrary, But should be construed as further including other elements. All terms, including technical and scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs, unless otherwise defined. Commonly used terms, such as predefined terms, should be interpreted to be consistent with the contextual meanings of the related art, and are not to be construed as ideal or overly formal, unless expressly defined to the contrary.

The foregoing description is merely illustrative of the technical idea of the present invention, and various changes and modifications may be made by those skilled in the art without departing from the essential characteristics of the present invention. Therefore, the embodiments disclosed in the present invention are intended to illustrate rather than limit the scope of the present invention, and the scope of the technical idea of the present invention is not limited by these embodiments. The scope of protection of the present invention should be construed according to the following claims, and all technical ideas within the scope of equivalents should be construed as falling within the scope of the present invention.

Claims (8)

A display panel in which pixels are defined along the intersection of the data line and the gate line;
A gate driver for supplying a scan signal to the gate line; And
A data driver for supplying a data voltage to the pixels through the data line and supplying a black data voltage to at least one pixel whose threshold voltage of the driving transistor is out of a predetermined range,
And an organic light emitting diode (OLED). The method according to claim 1,
Wherein the at least one pixel to which the black data voltage is supplied is a red pixel or a white pixel. The method according to claim 1,
A point for the image on the display panel is displayed by a combination of a red pixel, a green pixel, a blue pixel, and a white pixel,
The data driver may include:
Wherein when supplying the black data voltage to the white pixel of the point, the data voltage adjusted so that the point is displayed only by the red pixel, the green pixel and the blue pixel is supplied to each pixel. The method according to claim 1,
The data driver may include:
Supplying the black data voltage to a pixel whose threshold voltage of the driving transistor is out of a predetermined range at a first time point,
Wherein when the threshold voltage of the driving transistor of the pixel is restored within the predetermined range at the second time point, the black data voltage is not supplied to the pixel. The method according to claim 1,
The predetermined range is a range having a lower limit value,
The data driver may include:
Supplying the black data voltage to a pixel as long as the threshold voltage of the driving transistor is lower than or equal to the lower limit value at the first time point,
Wherein when the threshold voltage of the driving transistor of the pixel is greater than a hysteresis region of the lower limit value at the second time point, the black data voltage is not supplied to the pixel. The method according to claim 1,
Further comprising a reference voltage supply unit for supplying a reference voltage to the driving transistor source of the pixels,
The reference voltage supply unit supplies,
And supplies the reference voltage so that the driving transistor gate-source voltage (Vgs) of the at least one pixel to which the black data voltage is supplied becomes smaller. The method according to claim 6,
The reference voltage supply unit supplies,
And supplies a reference voltage higher than the other pixels to the at least one pixel. The method according to claim 6,
For two pixels supplied with a reference voltage through a common line,
The reference voltage supply unit supplies,
Supplying a reference voltage increased by the offset voltage to the common line so that the gate-source voltage of the driving transistor of the first pixel to which the black data voltage is supplied becomes smaller,
The data driver may include:
And supplies the data voltage increased by the offset voltage to the second pixel so that the gradation of the second pixel remains the same.

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