Patent Grant
9620056
This application claims priority to and the benefit of Korean Patent Application No. 10-2012-0148227, filed on Dec. 18, 2012, in the Korean Intellectual Property Office, the entire content of which is incorporated herein by reference.
1. Field
Embodiments relate to a pixel and an organic light emitting display using the same, and more particularly, to a pixel capable of displaying an image with uniform brightness and an organic light emitting display using the same.
2. Description of the Related Art
Recently, various flat panel displays (FPD) capable of reducing weight and volume that are disadvantages of cathode ray tubes (CRT) have been developed. The FPDs include liquid crystal displays (LCD), field emission displays (FED), plasma display panels (PDP), and organic light emitting displays.
Among the FPDs, the organic light emitting displays display images using organic light emitting diodes (OLED) that generate light by re-combination of electrons and holes. The organic light emitting display has high response speed and is driven with low power consumption.
The organic light emitting display includes a plurality of pixels arranged at intersections of a plurality of data lines, scan lines, and power supply lines in a matrix. Each of the pixels commonly includes an organic light emitting diode (OLED) and a driving transistor for controlling the amount of current that flows to the OLED. The pixels supply currents from the driving transistors to the OLEDs to correspond to data signals to generate light components with predetermined brightness components.
However, as illustrated in
As a result of experiment, in the organic light emitting display, deterioration of a response characteristic is caused by the characteristic of the driving transistor included in the pixel. That is, the threshold voltage of the driving transistor is shifted to correspond to the voltage applied to the driving transistor in a previous frame period so that light with desired brightness is not generated in the current frame.
In addition, in the conventional organic light emitting display, the OLED is deteriorated to correspond to use time. When the OLED is deteriorated, due to a change in efficiency, an image with desired brightness is not displayed. With the lapse of time, the OLED is deteriorated so that light with low brightness is generated to correspond to the same data signal.
Accordingly, embodiments are directed to providing a pixel capable of displaying an image with uniform brightness and an organic light emitting display using the same.
One or more embodiments provides a pixel, including an organic light emitting diode (OLED), a first transistor for controlling an amount of current that flows from a first power supply to a second power supply via the OLED to correspond to a voltage applied to a first node, a second transistor coupled between an anode electrode of the OLED and a feedback line, and having a gate electrode coupled to a control line, a third transistor coupled between the first node and a data line, and having a gate electrode coupled to a first scan line, a storage capacitor coupled between the first node and a second node, and a fourth transistor coupled between the second node and a reference power supply, and having a gate electrode coupled to a second scan line.
The third transistor may be turned on and off at least once in a partial period of a period in which the fourth transistor is turned on. The second transistor may be turned on so that a turn-on period thereof overlaps that of the fourth transistor in a specific frame period of a plurality of frames. The turn-on period of the second transistor may not overlap that of the third transistor.
The pixel may further include a fifth transistor coupled between the first power supply and the second node, and having a gate electrode coupled to an emission control line, and a sixth transistor coupled between a common terminal of the second transistor and the first transistor and the anode electrode of the OLED, and having a gate electrode coupled to the emission control line. A turn-on period of the fifth transistor may not overlap that of the fourth transistor in a remaining frame period excluding a frame in which deterioration information of the OLED is extracted among a plurality of frames.
The pixel may further include a fifth transistor coupled between the first power supply and the second node, and having a gate electrode coupled to an emission control line, and a sixth transistor coupled between a common terminal of the second transistor and the anode electrode of the OLED and the first transistor, and having a gate electrode coupled to the emission control line. A turn-on period of the fifth transistor may not overlap that of the fourth transistor in a remaining frame period excluding a frame in which threshold voltage information of the first transistor is extracted among a plurality of frames.
One or more embodiments provides an organic light emitting display, including a scan driver for driving first scan lines, second scan lines, and emission control lines, a control line driver for driving control lines, a data driver for driving data lines, pixels positioned at intersections of the first scan lines and the data lines, a sensing unit for extracting deterioration information of OLEDs included in the pixels in a first frame period of a plurality of frames and for extracting threshold voltage information of driving transistors included in the pixels in a second frame period, a timing controller for changing bits of first data items to correspond to the deterioration information and the threshold voltage information to generate second data items, and a data driver for supplying off data signals to the data lines in the first frame period, for supplying sensing data signals to the data lines in the second frame period, and for supplying data signals corresponding to the second data items to the data lines in remaining frames excluding the first frame period and the second frame period.
The sensing data signals may be set so that predetermined currents may flow from the driving transistors. The off data signals may be set so that the driving transistors may be turned off. The sensing unit may supply predetermined current to the feedback line in the first frame period to extract the deterioration information of the OLEDs and to extract the threshold voltage information of the driving transistors to correspond to amounts of currents supplied from the pixels to correspond to the sensing data signals in the second frame period.
Each of the pixels positioned in an ith horizontal line may include an OLED, a driving transistor for controlling an amount of current that flows from a first power supply to a second power supply via the OLED to correspond to a voltage applied to a first node, a second transistor coupled between an anode electrode of the OLED and a feedback line, and turned on when a control signal is supplied to an ith control line, a third transistor coupled between the first node and a data line, and turned on when a first scan signal is supplied to an ith first scan line, a storage capacitor coupled between the first node and a second node, and a fourth transistor coupled between the second node and a reference power supply, and turned on when a second scan signal is supplied to an ith second scan line.
The scan driver may supply a second scan signal to an ith second scan line to overlap a first scan signal supplied to an ith first scan line and to have a larger width than the first scan signal. The control line driver may supply a control signal to an ith control line to overlap the second scan signal supplied to the ith second scan line in the first frame period and the second frame period. The first scan signal supplied to the ith first scan line may not overlap the control signal supplied to the ith control line.
Each of the pixels positioned in the ith horizontal line may further include a fifth transistor coupled between the first power supply and the second node, and turned off when an emission control signal is supplied to an ith emission control line and otherwise turned on, and a sixth transistor coupled between a common terminal of the second transistor and the driving transistor and the anode electrode of the OLED, and simultaneously turned on and off with the fifth transistor. The scan driver may supply an emission control signal to an ith emission control line to overlap the second scan signal supplied to the ith second scan line in a remaining period excluding the first frame period.
Each of the pixels positioned in the ith horizontal line may further include a fifth transistor coupled between the first power supply and the second node, and turned off when an emission control signal is supplied to an ith emission control line and otherwise turned on, and a sixth transistor coupled between a common terminal of the second transistor and the anode electrode of the OLED and the driving transistor, and simultaneously turned on and off with the fifth transistor. The scan driver may supply an emission control signal to an ith emission control line to overlap the second scan signal supplied to the ith second scan line in a remaining period excluding the second frame period.
Korean Patent Application No. 10-2012-0148227, filed on Dec. 18, 2012, in the Korean Intellectual Property Office, and entitled: “Pixel and Organic Light Emitting Display Device Using the same” is incorporated by reference herein in its entirety.
Hereinafter, a pixel and an organic light emitting display using the same will be described in detail as follows with reference to
In addition, the organic light emitting display according to the present embodiment further includes a sensing unit 170 for extracting deterioration information of organic light emitting diodes (OLED) included in the pixels 140 and threshold voltage information of driving transistors included in the pixels 140 using feedback lines F1 to Fm.
The pixel unit 130 includes the pixels 140 positioned at the intersections of the first scan lines S11 to S1n, the second scan lines S21 to S2n, and the data lines D1 to Dm. During a sensing period, the pixels 140 transmit the deterioration information of the OLEDs and/or the threshold voltage information of the driving transistors to the feedback lines F1 to Fm and receive corrected data signals to correspond to the deterioration information and/or the threshold voltage information to the feedback lines F1 to Fm. The pixels 140 that receive the data signals control the amounts of currents supplied from a first power supply ELVDD to a second power supply ELVSS via OLEDs (see
The scan driver 110 supplies a first scan signal to the first scan lines S11 to S1n and supplies a second control signal to the second scan lines S21 to S2n. The scan driver 110 supplies emission control signals to the emission control lines E1 to En. Here, the first scan signal and the second scan signal are set to have voltages (for example, low voltages) at which transistors may be turned on and the emission control signals are set to have voltages (for example, high voltages) at which the transistors may be turned off. The supply types of the first scan signal, the second scan signal, and the emission control signals will be described in detail later.
The control line driver 160 supplies control signals to the control lines CL1 to CLn in the sensing period. For example, the control line driver 160 may sequentially supply the control signals to the control lines CL1 to CLn in a first sensing period for extracting the deterioration information and a second sensing period for extracting the threshold voltage information.
The data driver 120 receives second data data2 in a driving period and generates data signals using the received second data data2. The data signals generated by the data driver 120 are supplied to the data lines D1 to Dm in synchronization with scan signals. In addition, the data driver 120 supplies off data signals to the data lines D1 to Dm so that the driving transistors included in the pixels 140 may be turned off in the first sensing period and supplies sensing data signals to the data lines D1 to Dm so that predetermined currents may flow from the driving transistors included in the pixels 140 in the second sensing period, as will be described in detail later.
The sensing unit 170 extracts the deterioration information of the OLEDs included in the pixels 140 in the first sensing period and extracts the threshold voltage information of the driving transistors included in the pixels 140 in the second sensing period. For example, the sensing unit 170 supplies predetermined currents to the pixels 140 in the first sensing period and may extract the deterioration information using the voltages applied to the OLEDs to correspond to the supplied currents. In addition, the sensing unit 170 may extract the threshold voltage information of the driving transistors to correspond to the amounts of currents supplied from the pixels 140 to correspond to the sensing data signals in the second sensing period. The deterioration information and the threshold voltage information extracted by the sensing unit 170 are transmitted to the timing controller 150. The sensing unit 170 for compensating for the deterioration of the OLEDs and the threshold voltages of the driving transistors outside the pixels 140 may be realized by variety of currently known circuits.
The timing controller 150 controls the scan driver 110, the data driver 120, and the control line driver 160. In addition, the timing controller 150 changes first data data1 to correspond to the deterioration information and/or the threshold voltage information supplied from the sensing unit 170 to generate second data data2. Here, the second data data2 is set so that the deterioration of the OLEDs included in the pixels 140 and the threshold voltages of the driving transistors included in the pixels 140 may be compensated.
An anode electrode of the OLED is coupled to the pixel circuit 142 and a cathode electrode of the OLED is coupled to the second power supply ELVSS. The OLED generates light with predetermined brightness to correspond to the current supplied from the pixel circuit 142.
The pixel circuit 142 controls the amount of current supplied to the OLED to correspond to a data signal. For this purpose, the pixel circuit 142 includes first to sixth transistors M1 to M6 and a storage capacitor Cst.
A first electrode of the first transistor M1 is coupled to the first power supply ELVDD and a second electrode of the first transistor M1 is coupled to a first electrode of the sixth transistor M6. A gate electrode of the first transistor M1 is coupled to a first node N1. The first transistor M1 controls the amount of current supplied from the first power supply ELVDD to the second power supply ELVSS via the OLED to correspond to the voltage applied to the first node N1.
A first electrode of the second transistor M2 is coupled to the second electrode of the first transistor M1 and the second electrode of the second transistor M2 is coupled to the feedback line Fm. A gate electrode of the second transistor M2 is coupled to the control line CLn. The second transistor M2 is turned on when the control signal is supplied to the control line CLn to electrically couple the feedback line Fm and the second electrode of the first transistor M1 to each other.
A first electrode of the third transistor M3 is coupled to the data line Dm and a second electrode of the third transistor M3 is coupled to the first node N1. A gate electrode of the third transistor M3 is coupled to the first scan line S1n. The third transistor M3 is turned on when the first scan signal is supplied to the first scan line Sin to electrically couple the data line Dm and the first node N1 to each other.
A first electrode of the fourth transistor M4 is coupled to the reference power supply Vref and a second electrode of the fourth transistor M4 is coupled to the second node N2. A gate electrode of the fourth transistor M4 is coupled to the second scan line S2n. The fourth transistor M4 is turned on when the second scan signal is supplied to the second scan line S2n to supply the voltage of the reference power supply Vref to a second node N2.
A first electrode of the fifth transistor M5 is coupled to the first power supply ELVDD and a second electrode of the fifth transistor M5 is coupled to the second node N2. A gate electrode of the fifth transistor M5 is coupled to the emission control line En. The fifth transistor M5 is turned off when the emission control signal is supplied to the emission control line En and is otherwise turned on.
The first electrode of the sixth transistor M6 is coupled to a common terminal of the first transistor M1 and the second transistor M2 and a second electrode of the sixth transistor M6 is coupled to the anode electrode of the OLED. A gate electrode of the sixth transistor M6 is coupled to the emission control line En. The sixth transistor M6 is turned off when the emission control signal is supplied to the emission control line En and is otherwise turned on.
The storage capacitor Cst is coupled between the first node N1 and the second node N2. The storage capacitor Cst charges the voltage corresponding to a difference between the data signal and the reference power supply Vref. Here, voltage drop is not generated in the reference power supply Vref that does not supply current to the pixel. Therefore, a desired voltage may be charged in the storage capacitor Cst regardless of the voltage drop. The voltage value of the reference power supply Vref may vary with the data signal. For example, the voltage value may be the same as that of the first power supply ELVDD.
Referring to
After the emission control signal is supplied to the emission control line En, in a partial period of the first period T1, the second scan signal is supplied to the second scan line S2n. When the second scan signal is supplied to the second scan line S2n, the fourth transistor M4 is turned on. When the fourth transistor M4 is turned on, the voltage of the reference power supply Vref is supplied to the second node N2.
In a second period T2, the first scan signal is supplied to the first scan line S1n and the data signal DS is supplied to the data line Dm. When the first scan signal is supplied to the first scan line S1n, the third transistor M3 is turned on. When the third transistor M3 is turned on, the data signal from the data line Dm is supplied to the first node N1. At this time, the storage capacitor Cst charges the voltage corresponding to the difference voltage between the reference power supply Vref and the data signal. Here, since the voltage drop is not generated in the reference power supply Vref, the desired voltage may be charged in the storage capacitor Cst to correspond to the data signal.
Further, during the second period T2, when the data signal is supplied to the first node N1, the on bias voltage is applied to the first transistor M1. Actually, the first transistor M1 receives the on bias voltage from the point of time at which the data signal is supplied to the first node N1 to the point of time at which the supply of the second scan signal to the second scan line S2n is stopped, i.e., in the second period T2 and a third period T3. When the on bias voltage is supplied to the first transistor M1, the threshold voltage of the first transistor M1 is initialized to the on bias voltage. In this case, the first transistor M1 may control the amount of current supplied to the OLED so that an image with desired brightness may be displayed regardless of the data signal in a previous period.
On the other hand, on bias voltage supply time is controlled by the second scan signal supplied to the second scan line S2n. Therefore, according to the present embodiment, the second scan signal is supplied to the nth second scan line S2n to overlap the first scan signal supplied to the nth first scan line S1n and to have a larger width than that of the first scan signal. The emission control signal is supplied to the nth emission control line En to overlap the second scan signal supplied to the nth second scan line S2n and to have a larger width than that of the second scan signal so that unnecessary light is not generated by the pixel 140.
In a fourth period T4, the supply of the second scan signal to the second scan signal S2n is stopped. When the supply of the second scan signal to the second scan line S2n is stopped, the fourth transistor M4 is turned off so that electric coupling between the reference power supply Vref and the second node N2 is blocked.
In a fifth period T5, the supply of the emission control signal to the emission control line En is stopped. When the supply of the emission control signal to the emission control line En is stopped, the fifth transistor M5 and the sixth transistor M6 are turned on. When the fifth transistor M5 is turned on, the voltage of the first power supply ELVDD is supplied to the second node N2. At this time, since the first node N1 is floated, the storage capacitor Cst maintains the voltage charged in the previous period.
When the sixth transistor M6 is turned on, the first transistor M1 and the OLED are electrically coupled to each other. At this time, the first transistor M1 controls the amount of current that flows from the first power supply ELVDD to the second power supply ELVSS via the OLED to correspond to the voltage applied to the first node N1.
In practice, according to the present embodiment, the pixels 140 repeat the above-described processes in the driving period to realize a predetermined image. For example, the above-described processes may be sequentially performed in units of horizontal lines.
Referring to
In an 11th period T11, the first scan signal is supplied to the first scan line S1n and the sensing data signal is supplied to the data line Dm. When the first scan signal is supplied to the first scan line S1n, the third transistor M3 is turned on. When the third transistor M3 is turned on, the sensing signal SDS from the data line Dm is supplied to the first node N1. At this time, the storage capacitor Cst charges the voltage corresponding to a difference between the reference power supply Vref and the sensing data signal SDS.
In a 12th period T12, the control signal is supplied to the control line CLn. When the control signal is supplied to the control line CLn, the second transistor M2 is turned on. When the second transistor M2 is turned on, the feedback line Fm and the second electrode of the first transistor M1 are electrically coupled to each other. Then, predetermined current is supplied to the feedback line Fm via the first transistor M1 to correspond to the sensing data signal SDS. Here, the amount of current supplied from the first transistor M1 to the feedback line Fm is determined by the threshold voltage and mobility of the first transistor M1. That is, although the same sensing data signal SDS is supplied to all of the pixels 140, different currents flow in accordance with the threshold voltage and mobility of the first transistor M1. The sensing unit 170 extracts the threshold voltage information of the first transistor M1 to correspond to the amount of current supplied from the first transistor M1 and supplies the extracted information to the timing controller 150.
Then, in a 13th period T13, the first scan signal is supplied to the first scan line S1n and the data signal DS is supplied in synchronization with the first scan signal. When the first scan signal is supplied to the first scan line S1n, the third transistor M3 is turned on so that the data signal DS from the data line Dm is supplied to the first node N1. At this time, the storage capacitor Cst charges the voltage corresponding to the difference between the data signal DS and the reference power supply Vref.
In a 14th period T14, the supply of the second scan signal to the second scan line S2n is stopped so that the fourth transistor M4 is turned off. In a 15th period T15, the supply of the emission control signal to the emission control line En is stopped so that the fifth transistor M5 and the sixth transistor M6 are turned on. At this time, the first transistor M1 controls the amount of current that flows from the first power supply ELVDD to the second power supply ELVSS via the OLED to correspond to the voltage applied to the first node N1.
In practice, according to the present embodiment, the pixels 140 repeat the above-described processes in the second sensing period to sense the threshold voltage of each driving transistor. For example, the above-described processes may be sequentially performed in units of horizontal lines.
Referring to
In a 21st period t21, the first scan signal is supplied to the first scan line S1n and the off data signal ODS is supplied to the data line Dm. When the first scan signal is supplied to the first scan line S1n, the third transistor M3 is turned on. When the third transistor M3 is turned on, the off data signal ODS from the data line Dm is supplied to the first node N1. Here, the off data signal ODS is set to have a voltage at which the first transistor M1 may be turned off.
In a 22nd period T22, the control signal is supplied to the control line CLn. When the control signal is supplied to the control line CLn, the second transistor M2 is turned on. When the second transistor M2 is turned on, the feedback line Fm and the anode electrode of the OLED are electrically coupled to each other. Then, in the 22nd period T22, predetermined current is supplied from the sensing unit 170 to the feedback line Fm. The predetermined current supplied to the feedback line Fm is supplied to the OLED so that a predetermined voltage is applied to the OLED. Here, the resistance value of the OLED changes to correspond to deterioration. Therefore, the voltage applied to the OLED to correspond to the predetermined current includes the deterioration information of the OLED. The sensing unit 170 extracts the deterioration information using the predetermined voltage applied to the OLED and supplies the extracted deterioration information to the timing controller 150.
Then, in a 23rd period T23, the first scan signal is supplied to the first scan line S1n and the data signal DS is supplied in synchronization with the first scan signal. When the first scan signal is supplied to the first scan line S1n, the third transistor M3 is turned on so that the data signal DS from the data line Dm is supplied to the first node N1. At this time, the storage capacitor Cst charges the voltage corresponding to the difference between the data signal DS and the reference power supply Vref.
In a 24th period T24, the supply of the second scan signal to the second scan line S2n is stopped so that the fourth transistor M4 is turned off. In a 25th period T25, the supply of the emission control signal to the emission control line En is stopped so that the fifth transistor M5 and the sixth transistor M6 are turned on. At this time, the first transistor M1 controls the amount of current that flows from the first power supply ELVDD to the second power supply ELVSS via the OLED to correspond to the voltage applied to the first node N1.
In practice, according to the present embodiment, the pixels 140 repeat the above-described processes in the first sensing period to sense deterioration information of each OLED. For example, the above-described processes may be sequentially performed in units of horizontal lines.
According to the present embodiment, the driving period, the first sensing period, and the second sensing period are appropriately arranged in units of frames. For example, the pixels may be driven by waveforms of the driving period in most frames and may be driven by waveforms of the first sensing period and the second sensing period in specific frames. Then, in the specific frames, the deterioration information of the OLEDs and the threshold voltage information of the driving transistors are extracted. Then, the timing controller 150 changes the first data data1 so that the deterioration of the OLEDs included in the pixels 140 and the threshold voltages of the driving transistors included in the pixels 140 may be compensated for using the deterioration information and the threshold voltage information to generate the second data data2. Therefore, in the driving period, the pixels 140 may realize an image with uniform brightness regardless of the deterioration of the OLEDs.
The sixth transistor M6′ included in the pixel circuit 142′ is coupled between the common node of the second transistor M2 and the OLED, and the second electrode of the first transistor M1. The sixth transistor M6′ is turned off when the emission control signal is supplied to the emission control line En and is otherwise turned on.
The pixel according to the second embodiment is driven by the driving waveforms of
Referring to
In addition, when the sixth transistor M6′ is turned on, in a period where the second transistor M2 is turned on, the first transistor M1 and the feedback line Fm are electrically coupled to each other. That is, the current corresponding to the sensing data signal SDS may be stably supplied from the first transistor M1 to the feedback line Fm via the sixth transistor M6′ and the second transistor M2. Here, in order to improve reliability of the operation, in a period where the control signal is supplied to the control line CLn, the voltage of the second power supply ELVSS may be increased so that the current does not flow to the OLED.
Referring to
Therefore, in the case of the waveforms of
By way of summation and review, the pixel according to embodiments and the organic light emitting display using the same, an on bias voltage is applied to the driving transistor before a data signal is supplied so that the characteristic of the driving transistor is initialized. In this case, the driving transistor may supply desired current to the OLED regardless of the data signal of a previous period so that an image with uniform brightness may be displayed. In addition, according to embodiments, the deterioration information of the OLED and the threshold voltage information of the driving transistor are extracted, at least in specific frames, and data is changed to correspond to the extracted information so that an image with uniform brightness may be displayed.
While the present invention has been described in connection with certain exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims, and equivalents thereof.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2012-0148227 | Dec 2012 | KR | national |
| Number | Name | Date | Kind |
|---|---|---|---|
| 20070024541 | Ryu et al. | Feb 2007 | A1 |
| 20070024543 | Chung | Feb 2007 | A1 |
| 20070085781 | Chung et al. | Apr 2007 | A1 |
| 20070215888 | Mitsuhashi | Sep 2007 | A1 |
| 20080036710 | Kim | Feb 2008 | A1 |
| 20080048560 | Sung et al. | Feb 2008 | A1 |
| 20090027423 | Kwon | Jan 2009 | A1 |
| 20100188320 | Min et al. | Jul 2010 | A1 |
| 20100220038 | Chung et al. | Sep 2010 | A1 |
| 20110227505 | Park | Sep 2011 | A1 |
| Number | Date | Country |
|---|---|---|
| 10-2008-0018557 | Feb 2008 | KR |
| 10-2010-0086877 | Aug 2010 | KR |
| 10-2011-0104705 | Sep 2011 | KR |
| Number | Date | Country | |
|---|---|---|---|
| 20140168290 A1 | Jun 2014 | US |
