Pixel, organic light emitting display using the same, and associated methods

• US 8,149,186 B2
• Filed: 04/10/2008
• Issued: 04/03/2012
• Est. Priority Date: 04/10/2007
• Status: Active Grant

• Current Assignee: Samsung Display Company Limited (Samsung Electronics Co. Ltd.)
• Original Assignee: Samsung Mobile Display Company Limited (Samsung Electronics Co. Ltd.)
• Inventors: Kim, Yang-Wan
• Primary Examiner(s): Mengistu, Amare
• Assistant Examiner(s): Khoo, Stacy
• Application Number:
  US12/081,105
• Publication Number:
  US 20090027310A1
• Time in Patent Office: 1,454 Days
• Field of Search: 345/76, 345/77, 345/82, 326/82, 326/83, 313/486, 313/500, 313505-507, 315/169.3, 327108-112
• US Class Current: 345/76
• CPC Class Codes: G09G 2300/0819 used for counteracting undesired variations, e.g. feedback or autozeroing
• CPC Class Codes: G09G 2300/0852 being a dynamic memory with more than one capacitor
• CPC Class Codes: G09G 2320/043 Preventing or counteracting the effects of ageing
• CPC Class Codes: G09G 2320/045 Compensation of drifts in the characteristics of light emitting or modulating elements
• CPC Class Codes: G09G 3/3233 with pixel circuitry controlling the current through the light-emitting element

Abstract

A pixel including an organic light emitting diode, a second transistor controlling a current supplied to the organic light emitting diode, a pixel circuit configured to compensate a threshold voltage of the second transistor; and a compensating unit controlling a voltage of a gate electrode of the second transistor in order to compensate for deterioration of the organic light emitting diode. The compensating unit includes seventh and eighth transistors coupled in series between the organic light emitting diode and a first power source, the seventh and eight transistors being commonly connected to a fourth node therebetween, first and second feedback capacitors coupled in series between the fourth node and a second node, the second node being coupled to the gate electrode of the second transistor, and a ninth transistor coupled between a predetermined voltage source and a fifth node that is common to the first and second feedback capacitors.

Claims

1. A pixel, comprising:

an organic light emitting diode;

a first transistor controlling a current supplied to the organic light emitting diode;

a pixel circuit configured to compensate a threshold voltage of the first transistor; and

a compensating unit controlling a voltage of a gate electrode of the first transistor in order to compensate for deterioration of the organic light emitting diode, wherein the compensating unit includes;

second and third transistors coupled in series between the organic light emitting diode and a first power source, the second and third transistors being commonly connected to a first node therebetween,

first and second feedback capacitors coupled in series between the first node and a second node, the second node being coupled to the gate electrode of the first transistor, and

a fourth transistor coupled between a predetermined voltage source and a third node that is common to the first and second feedback capacitors, wherein the pixel circuit includes;

a fifth transistor having a gate electrode coupled to an i^th scan line, the fifth transistor being turned-on to couple a data line to a first electrode of the first transistor when a scan signal is supplied to the i^th scan line,

a sixth transistor having a gate electrode coupled to the i^th scan line, the sixth transistor being turned-on to couple a second electrode of the first transistor to the second node when the scan signal is supplied to the i^th scan line,

a seventh transistor having a gate electrode coupled to an i−

1^th scan line, the seventh transistor being turned-on to couple an initialization power source to the second node when a scan signal is supplied to the i−

1^th scan line,

an eighth transistor having a gate electrode coupled to an i^th light emitting control line, the eighth transistor being turned-on to couple the first electrode of the first transistor to the first power source when a light emitting control signal is not supplied to the i^th light emitting control line,

a ninth transistor having a gate electrode coupled to the i^th light emitting control line, the ninth transistor being turned-on to couple the second electrode of the first transistor to the organic light emitting diode when the light emitting control signal is not supplied to the i^th light emitting control line, and

a storage capacitor coupled between the second node and the first power source, wherein;

the i^th scan line is defined with i as a natural number; and

the i^th light emitting control line is defined with i as a natural number.

2. The pixel as claimed in claim 1, wherein the predetermined voltage source is the initialization power source.

3. The pixel as claimed in claim 1, wherein the second and third transistors operate in opposition to one another.

4. The pixel as claimed in claim 1, wherein the third and fourth transistors operate in opposition to one another.

5. The pixel as claimed in claim 4, wherein the third transistor is a PMOS transistor and the fourth transistor is an NMOS transistor.

6. The pixel as claimed in claim 1, wherein the predetermined voltage source is the first power source.

7. The pixel as claimed in claim 1, wherein:

the second and third transistors have gate electrodes coupled to an i+2^th light emission control line, and

the second transistor is an NMOS transistor and the third transistor is a PMOS transistor.

8. A display, comprising;

a scan driver coupled to scan lines and light emitting control lines;

a data driver coupled to data lines; and

a plurality of pixels as claimed in claim 1, the pixels being coupled to the scan lines, the data lines, and the light emitting control lines.

9. The display as claimed in claim 8, wherein the initialization power source is set to a voltage that is lower than a voltage of a data signal applied to the data line.

10. The display as claimed in claim 8, wherein:

the scan driver supplies a light emitting control signal to the i^th light emitting control line such that it overlaps with scan signals supplied to the i−

1^th scan line and the i^th scan line, and

the scan driver supplies a light emitting control signal to an i+1^th light emitting control line such that it overlaps with scan signals supplied to the i^th scan line and an i+1^th scan line.

11. The display as claimed in claim 10, wherein:

the second transistor is turned on when the scan signal is supplied to the i+1^th scan line, and

the third transistor is turned off when the light emitting control signal is supplied to the i+1^th light emitting control line.

12. The display as claimed in claim 11, wherein the third and fourth transistors operate in opposition to one another.

13. The display as claimed in claim 12, wherein the third transistor is a PMOS transistor and the fourth transistor is an NMOS transistor.

14. The display as claimed in claim 10, wherein:

the scan driver supplies a light emitting control signal to an i+2^th light emitting control line such that it overlaps with the scan signal supplied to the i+2^th scan line,

the second transistor is turned on when the light emitting control signal is supplied to the i+2^th light emitting control line, and the third transistor is turned off when the light emitting control signal is supplied to the i+2^th light emitting control line.

15. The display as claimed in claim 14, wherein:

the second and third transistors have gate electrodes coupled to the i+2^th light emission control line,

the second transistor is an NMOS transistor, and

the third transistor is a PMOS transistor.

16. The display as claimed in claim 14, wherein the predetermined voltage source is the initialization power source.

17. The display as claimed in claim 8, wherein:

the initialization power source initializes a voltage of the gate electrode of the first transistor, and

the sixth transistor diode-connects the first transistor to charge a voltage corresponding to a threshold voltage of the first transistor and a data signal in the storage capacitor.

18. The display as claimed in claim 17, wherein:

the second transistor couples the first node to the organic light emitting diode while a current is supplied to the organic light emitting diode, such that a voltage at the organic light emitting diode is applied to the first node,

subsequently, the third transistor couples the first node to the first power source, such that the voltage of the first node is raised to the voltage of the first power source, and

the first and second feedback capacitors transmit the voltage rise of the first node to the second node.

19. The display as claimed in claim 8, wherein the second and third transistors operate in opposition to one another.

20. A method of driving a display having first and second transistors coupled in series between an anode electrode of an organic light emitting diode and a first power source, and first feedback and second feedback capacitors coupled in series between a first node, which is a node common to the first and second transistors, and a gate electrode of a driving transistor, the method including:

initializing a voltage of the gate electrode of the driving transistor with a voltage of an initialization power source;

charging a voltage corresponding to a threshold voltage of the driving transistor and a data signal in a storage capacitor by diode-connecting the driving transistor;

supplying a current corresponding to the voltage charged in the storage capacitor to the organic light emitting diode;

applying a voltage applied to the organic light emitting diode to the first node;

maintaining a second node, which is common to the first and second feedback capacitors, at a constant voltage while charging the voltage in the storage capacitor and supplying the voltage applied to the organic light emitting diode to the first node; and

controlling the voltage of the gate electrode of the driving transistor by setting the second node to a floating state and, at the same time, raising the voltage of the first node to the voltage of the first power source.

21. The method as claimed in claim 20, wherein the constant voltage is the voltage supplied from any one of the initialization power source and the first power source.

22. The method as claimed in claim 20, wherein the initialization power source is set to a voltage that is lower than that of the data signal.

23. The method as claimed in claim 20, wherein the first and second transistors operate in opposition to one another.

24. A pixel, comprising:

an organic light emitting diode;

a first transistor controlling a current supplied to the organic light emitting diode;

a pixel circuit configured to compensate a threshold voltage of the first transistor; and

a compensating unit controlling a voltage of a gate electrode of the first transistor in order to compensate for deterioration of the organic light emitting diode, wherein the compensating unit includes;

second and third transistors coupled in series between the organic light emitting diode and a first power source, the second and third transistors operating in opposition to one another, the second and third transistors being commonly connected to a first node therebetween,

first and second feedback capacitors coupled in series between the first node and a second node, the second node being coupled to the gate electrode of the first transistor, and

a fourth transistor coupled between a predetermined voltage source and a third node that is common to the first and second feedback capacitors, wherein;

the second and third transistors are coupled in series between the organic light emitting diode and the first power source such that placing the second transistor in an ‘

on’

state and, at the same time, placing the third transistor in an ‘

on’

state would allow an electric current to flow from the first power source through the third transistor to the second transistor and then to the organic light emitting diode, and

the fourth transistor is coupled between the predetermined voltage source and the third node such that placing the fourth transistor in an ‘

on’

state would allow an electric current to flow from the predetermined voltage source through the fourth transistor to the third node.

25. A display, comprising;

a scan driver coupled to scan lines and light emitting control lines;

a data driver coupled to data lines; and

a plurality of pixels as claimed in claim 24, the pixels being coupled to the scan lines, the data lines, and the light emitting control lines.