Pixel, organic light emitting display using the same, and associated methods
View Patent ↗A pixel including an OLED, the pixel including a first transistor coupled between a data line and a first node, the first transistor being turned on by a low signal on an i-th scan line, a second transistor coupled between a first power source and a fifth transistor, a third transistor coupled between the gate electrode of the second transistor and an electrode of the second transistor that is coupled to the fifth transistor, the third transistor being turned on by a low signal on an (i−1)-th scan line, a fourth transistor coupled between a first reference voltage and the first node, the fourth transistor being turned on by the low signal on the (i−1)-th scan line, a storage capacitor coupled between the first node and the second node, and a compensator controlling a voltage of the second node corresponding to degradation of the OLED.
1. A pixel, comprising:
an OLED;
a first transistor coupled between a data line and a first node, the first transistor being turned on by a low signal on an i-th scan line, i being a natural number;
a second transistor coupled between a first power source and a fifth transistor, wherein:
the second transistor has a gate electrode coupled to a second node,
the fifth transistor is coupled between the second transistor and the OLED, and
the fifth transistor is turned on by a low signal on an i-th emission control line;
a third transistor coupled between the gate electrode of the second transistor and an electrode of the second transistor that is coupled to the fifth transistor, the third transistor being turned on by a low signal on an (i−1)-th scan line;
a fourth transistor coupled between a first reference voltage and the first node, the fourth transistor being turned on by the low signal on the (i−1)-th scan line;
a storage capacitor coupled between the first node and the second node; and
a compensator controlling a voltage of the second node corresponding to degradation of the OLED,
wherein the compensator includes:
a feedback capacitor coupled between the first node and a third node; and
a sixth transistor and a seventh transistor disposed in series between a second reference voltage and a fourth node, wherein:
the third node is between the sixth and seventh transistors, and
the fourth node is between the fifth transistor and the OLED.
2. The pixel as claimed in claim 1 , wherein the voltage of the second node is controlled to increase a voltage applied to the OLED as the resistance of the OLED increases.
3. The pixel as claimed in claim 1 , wherein:
the sixth transistor is coupled between the third node and the fourth node,
the seventh transistor is coupled between the second reference voltage and the third node,
the sixth transistor is turned on by the low signal on the i-th scan line, and
the seventh transistor is turned off by the low signal on the i-th scan line.
4. The pixel as claimed in claim 1 , wherein:
a voltage of the third node is set to a voltage applied to the OLED when the sixth transistor is turned on, and
the voltage of the third node is increased from the voltage applied to the OLED to the second reference voltage when the seventh transistor is turned on.
5. The pixel as claimed in claim 4 , wherein the feedback capacitor transfers a voltage change of the third node to the first node.
6. The pixel as claimed in claim 1 , wherein:
the first reference voltage is set to a voltage of the first power source, and the second reference voltage is set to the first reference voltage.
7. The pixel as claimed in claim 1 , wherein the first reference voltage is set to a voltage of the first power source.
8. The pixel as claimed in claim 1 , wherein the first transistor is turned on by the low signal on the i-th scan line after the third and fourth transistors are turned on by the low signal on the (i−1)-th scan line.
9. The pixel as claimed in claim 8 , wherein:
the fifth transistor is turned off by a high signal on the i-th emission control line after the third and fourth transistors are turned on by the low signal on the on the (i−1)-th scan line, and
the fifth transistor is turned on by the low signal on the i-th emission control line before the first transistor is turned on by the low signal on the i-th scan line.
10. An organic light emitting display, comprising:
a scan driver coupled to scan lines and emission control lines;
a data driver coupled data lines; and
pixels including respective OLEDs, wherein the pixels are coupled to respective scan, emission control, and data lines, and include:
a first transistor coupled between a data line and a first node, the first transistor being turned on by a low signal on an i-th scan line, i being a natural number;
a second transistor coupled between a first power source and a fifth transistor, wherein:
the second transistor has a gate electrode coupled to a second node,
the fifth transistor is coupled between the second transistor and the OLED, and
the fifth transistor is turned on by a low signal on an i-th emission control line;
a third transistor coupled between the gate electrode of the second transistor and an electrode of the second transistor that is coupled to the fifth transistor, the third transistor being turned on by a low signal on an (i−1)-th scan line;
a fourth transistor coupled between a first reference voltage and the first node, the fourth transistor being turned on by the low signal on the (i−1)-th scan line;
a storage capacitor coupled between the first node and the second node; and
a compensator controlling a voltage of the second node corresponding to degradation of the OLED,
wherein the compensator includes:
a feedback capacitor coupled between the first node and a third node; and
a sixth transistor and a seventh transistor disposed in series between a second reference voltage and a fourth node, wherein:
the third node is between the sixth and seventh transistors, and
the fourth node is between the fifth transistor and the OLED.
11. The organic light emitting display as claimed in claim 10 , wherein the scan driver supplies a scan signal to be provided to an i-th scan line and an emission control signal to be provided to an i-th emission control line to overlap with each other during a partial time period.
12. The organic light emitting display as claimed in claim 11 , wherein the emission control signal is supplied to the i-th emission control line when a predetermined time elapses after the scan signal is supplied to the i-th scan line.
13. A method for driving a display, comprising:
initializing a gate electrode of a drive transistor during an initial time period while a low scan signal is supplied to an (i−1)-th scan line, i being a natural number;
supplying a high emission control signal to an i-th emission control line after the initial time period and maintaining the high emission control signal while the low scan signal is supplied to the (i−1)-th scan line in order to charge a storage capacitor with a voltage corresponding to a threshold voltage of the drive transistor;
charging the storage capacitor with a voltage corresponding to a data signal while a low scan signal is supplied to an i-th scan line; and
controlling a voltage of the gate electrode of the drive transistor in correspondence with degradation of an OLED,
wherein controlling the voltage of the gate electrode of the drive transistor includes:
providing an anode voltage of an anode electrode of the OLED to a first terminal of a feedback capacitor while the low scan signal is supplied to the i-th scan line; and
increasing a first terminal voltage of the first terminal of the feedback capacitor while a high scan signal is supplied to the i-th scan line, wherein:
a second terminal of the feedback capacitor is coupled to a first terminal of the storage capacitor, and
a second terminal of the storage capacitor is coupled to the gate electrode of the drive transistor.
14. The method as claimed in claim 13 , wherein initializing the gate electrode of the drive transistor during the initial time period includes applying a first reference voltage to a first electrode of a storage capacitor, a second electrode of the storage capacitor being coupled to the gate electrode of the drive transistor.
15. The method as claimed in claim 13 , wherein controlling the voltage of the gate electrode of the drive transistor further includes reducing a voltage change of the first terminal of the feedback capacitor in correspondence with increasing resistance of the OLED.
16. The method as claimed in claim 15 , wherein controlling the voltage of the gate electrode of the drive transistor further includes reducing the voltage of the gate electrode of the drive transistor in correspondence with the reduction in the voltage change of the first terminal of the feedback capacitor.
17. The method as claimed in claim 16 , wherein controlling the voltage of the gate electrode of the drive transistor further includes increasing an electric current supplied to the OLED by the drive transistor in correspondence with the reduction in the voltage of the gate electrode of the drive transistor.
18. The method as claimed in claim 13 , wherein controlling the voltage of the gate electrode of the drive transistor further includes increasing the first terminal voltage of the first terminal of the feedback capacitor to a second reference voltage while the high scan signal is supplied to the i-th scan line.
19. The method as claimed in claim 13 , wherein:
a scan signal having a low pulse is supplied to the (i−1)-th scan line and subsequently supplied to the i-th scan line,
an emission control signal having a high pulse is supplied to the i-th emission control line,
the emission control signal on the i-th emission control line transitions high after the scan signal on the (i−1)-th scan line transitions low, and
the emission control signal on the i-th emission control line transitions low after the scan signal on the (i−1)-th scan line transitions high.