SYSTEMS AND METHODS FOR AGING COMPENSATION IN AMOLED DISPLAYS

• US 20120299978A1
• Filed: 05/26/2012
• Published: 11/29/2012
• Est. Priority Date: 05/27/2011
• Status: Active Grant

• Current Assignee: IGNIS Innovation Incorporated
• Original Assignee: IGNIS Innovation Incorporated
• Inventors: Chaji, Gholamreza
• Granted Patent: US 9,773,439 B2
• Time in Patent Office: Days
• US Class Current: 345/690
• CPC Class Codes: G09G 2230/00 Details of flat display driving waveforms
• CPC Class Codes: G09G 2320/0295 by monitoring each display pixel
• 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 2330/12 Test circuits or failure detection circuits included in a display system, as permanent part thereof
• CPC Class Codes: G09G 3/006 Electronic inspection or testing of displays and display drivers, e.g. of LED or LCD displays testing individual LED's G01R31/2635; testing lamps G01R31/44; testing of optical features of LCD displays G02F1/1309
• CPC Class Codes: G09G 3/3233 with pixel circuitry controlling the current through the light-emitting element
• CPC Class Codes: G09G 3/3291 in which the data driver supplies a variable data voltage for setting the current through, or the voltage across, the light-emitting elements

Abstract

Circuits for programming, monitoring, and driving pixels in a display are provided. Circuits generally include a driving transistor to drive current through a light emitting device according to programming information which is stored on a storage device, such as a capacitor. One or more switching transistors are generally included to select the circuits for programming, monitoring, and/or emission. Circuits advantageously incorporate emission transistors to selectively couple the gate and source terminals of a driving transistor to allow programming information to be applied to the driving transistor independently of a resistance of a switching transistor.

Claims

1. A system for compensating a pixel in a display array, the system comprising:

a pixel circuit for being programmed according to programming information, during a programming cycle, and driven to emit light according to the programming information, during an emission cycle, the pixel circuit including;

a light emitting device for emitting light during the emission cycle,

a driving transistor for conveying current through the light emitting device during the emission cycle,

a storage capacitor for being charged with a voltage based at least in part on the programming information, during the programming cycle, and

an emission control transistor arranged to selectively connect, during the emission cycle, at least two of the light emitting device, the driving transistor, and the storage capacitor, such that current is conveyed through the light emitting device via the driving transistor according to the voltage on the storage capacitor; and

a driver for programming the pixel circuit via a data line by charging the storage capacitor according to the programming information;

a monitor for extracting a voltage or a current indicative of aging degradation of the pixel circuit; and

a controller for operating the monitor and the driver and configured to;

receive an indication of the amount of degradation from the monitor;

receive a data input indicative of an amount of luminance to be emitted from the light emitting device;

determine an amount of compensation to provide to the pixel circuit based on the amount of degradation; and

provide the programming information to the driver to program the pixel circuit, wherein the programming information is based at least in part on the received data input and the determined amount of compensation.

2. The system according to claim 1, wherein the pixel circuit further includes:

a data switch transistor, operated according to a select line, for coupling the source terminal of the driving transistor to the data line, the data line being coupled to the monitor for measuring a current through the driving transistor during a monitoring cycle.

3. The system according to claim 2, wherein the data switch transistor is coupled to the light emitting device, and wherein the data line is fixed at a calibration voltage during the monitoring cycle, the calibration voltage being sufficient to turn off the light emitting device such that, during the monitoring cycle, current through the driving transistor is not conveyed through the light emitting device.

4. The system according to claim 2, wherein the monitor includes a voltage monitor for monitoring an operating voltage of the light emitting device via the data switch transistor.

5. The system according to claim 1, wherein the emission control transistor is connected between the gate terminal of the driving transistor and the storage capacitor such that the gate terminal of the driving transistor is isolated from the storage capacitor, during the programming cycle while the emission control transistor is turned off.

6. The system according to claim 5, further comprising a reference switch transistor connected between the storage capacitor and a reference line, such that the storage capacitor is charged, during the programming cycle, according to a difference between a reference voltage applied to the reference line and a programming voltage applied on the data line.

7. The system according to claim 6, wherein the reference line provides a compensation voltage, during the programming phase, the compensation voltage being based on the amount of compensation determined by the controller.

8. The system according to claim 1, further comprising:

a data switch transistor operated according to a select line, for coupling a source terminal of the driving transistor to the data line, during programming and monitoring cycles;

a first reference switch transistor operated according to the select line, for coupling the gate terminal of the driving transistor to a first reference line, during the programming cycle, such that the driving transistor is turned off during the programming cycle; and

a second reference switch transistor operated according to the select line, for coupling a second reference line to a terminal of the storage capacitor other than one connected to the data switch transistor, such that the storage capacitor is charged, during the programming cycle while the data switch transistor, first reference switch transistor, and second reference transistor are turned on, according to a difference between a programming voltage applied on the data line and a reference voltage or compensation voltage on the second reference line.

9. The system according to claim 8, wherein the data line is coupled to the monitor for measuring a current through the driving transistor during a monitoring cycle of the pixel circuit.

10. The system according to claim 8, further comprising a plurality of similar pixel circuits arranged in rows and columns to form a display panel, and wherein the controller is further configured to receive an indication of aging degradation for each of the plurality of pixel circuits, determine an amount of degradation for each of the plurality of pixel circuits, and program each of the plurality of pixel circuits according to the respective determined amounts of compensation.

11. The system according to claim 1, wherein the emission control transistor couples the storage capacitor across a gate terminal and a source terminal of the driving transistor during the emission cycle, the pixel circuit further comprising:

a data switch transistor, operated according to a select line, for coupling the data line to a terminal of the storage capacitor coupled to the gate terminal of the driving transistor; and

a monitoring switch transistor, operated according to the select line, for coupling a monitor line to a terminal of the storage capacitor coupled to the emission transistor, the monitor line being coupled to the monitor for measuring the current through the drive transistor during the monitoring cycle.

12. The system according to claim 11, wherein the monitor line is fixed at a calibration voltage during the monitoring cycle, the calibration voltage being sufficient to turn off the light emitting device such that, during the monitoring cycle, current through the driving transistor is not conveyed through the light emitting device

13. The system according to claim 11, wherein the emission control transistor is coupled between the storage capacitor and the light emitting device, thereby isolating the storage capacitor from the light emitting device, during the programming phase, so as to prevent the voltage applied to the storage capacitor from being influenced by an internal capacitance of the light emitting device.

14. The system according to claim 11, wherein the emission control transistor is coupled between the source terminal of the driving transistor and the light emitting device, thereby preventing the driving transistor from conveying current to the light emitting device while the emission control transistor is switched off.

15. The system according to claim 14, wherein a terminal of the emission transistor coupled to the driving transistor is also coupled to the storage capacitor and the monitoring switch transistor.

16. The system according to claim 1, wherein the pixel circuit further includes:

a data switch transistor, operated according to a first select line, for coupling the data line to a terminal of the storage capacitor coupled to the gate terminal of the driving transistor; and

a monitoring switch transistor, operated according to a second select line, for coupling the data line to a terminal of the storage capacitor coupled to the emission transistor, the monitor line being coupled to the monitor for measuring the current through the drive transistor during the monitoring phase.

17. The system according to claim 1, wherein the light emitting device is an organic light emitting diode.

18. A pixel circuit for driving a light emitting device, the pixel circuit comprising:

a driving transistor for driving current through a light emitting device according to a driving voltage applied across the driving transistor;

a storage capacitor for being charged, during a programming cycle, with the driving voltage;

an emission control transistor for connecting at least two of the driving transistor, the light emitting device, and the storage capacitor, such that current is conveyed through the driving transistor, during the emission cycle, according to voltage charged on the storage capacitor; and

at least one switch transistor for connecting a current path through the driving transistor to a monitor for receiving indications of aging information based on the current through the driving transistor, during a monitoring cycle.

19. The pixel circuit according to claim 18, wherein the emission control transistor is connected in series with the light emitting device so as to prevent the driving transistor from conveying a current through the at least one switch transistor while the pixel circuit is being programmed during the programming cycle.

20. The pixel circuit according to claim 19, wherein the pixel circuit is programmed independent of a resistance of the at least one switch transistor.

21. The pixel circuit according to claim 18, wherein the storage capacitor is connected across a gate terminal and a source terminal of the driving transistor during the emission cycle via the emission control transistor, and wherein the storage capacitor is disconnected from at least one of the gate terminal or the source terminal of the driving transistor during a programming cycle.

22. The pixel circuit according to claim 18, further including:

a data switch transistor, operated according to a select line, for coupling, during the programming cycle, the data line to a terminal of the storage capacitor coupled to the gate terminal of the driving transistor; and

wherein the at least one switch transistor is a monitoring switch transistor, operated according to the select line or another select line, for conveying a current or voltage indicative of an amount of degradation of the pixel circuit to the monitor, during the monitoring cycle, the monitoring switch transistor being coupled to both the emission control transistor and the storage capacitor.

23. The pixel circuit according to claim 18, wherein the emission transistor and the storage capacitor are coupled in series between the gate terminal and source terminal of the driving transistor.

24. The pixel circuit according to claim 18, wherein the light emitting device includes an organic light emitting diode.

25. A pixel circuit for driving a light emitting device, the pixel circuit comprising:

a driving transistor for driving current through a light emitting device according to a driving voltage applied across the driving transistor;

a storage capacitor for being charged, during a programming cycle, with the driving voltage;

one or more switch transistors for connecting the storage capacitor to one or more data lines or reference lines providing voltages sufficient to charge the storage capacitor with the driving voltage, during the programming cycle; and

an emission control transistor, operated according to an emission line, for disconnecting the storage capacitor from the light emitting device during the programming cycle, such that the storage capacitor is charged independent of the capacitance of the light emitting device.

26. The pixel circuit according to claim 25, wherein the emission control transistor is connected in series between the driving transistor and the light emitting device such that the light emitting device receives current from the driving transistor while the emission control transistor is turned on.

27. A display system comprising:

a pixel circuit for being programmed according to programming information, during a programming cycle, and driven to emit light according to the programming information, during an emission cycle, the pixel circuit including;

a light emitting device for emitting light during the emission cycle,

a driving transistor for conveying current through the light emitting device during the emission cycle, the current being conveyed according to a voltage across a gate and a source terminal of the driving transistor,

a storage capacitor for being charged with a voltage based at least in part on the programming information, during the programming cycle, the storage capacitor connected across the gate and source terminals of the driving transistor, and

a first switch transistor connecting the source terminal of the driving transistor to a data line;

a driver for programming the pixel circuit via the data line by applying a voltage to a terminal of the storage capacitor that is connected to the source terminal of the driving transistor;

a monitor for extracting a voltage or a current indicative of aging degradation of the pixel circuit; and

a controller for operating the monitor and the driver and configured to;

receive an indication of the amount of degradation from the monitor;

receive a data input indicative of an amount of luminance to be emitted from the light emitting device;

determine an amount of compensation to provide to the pixel circuit based on the amount of degradation; and

provide the programming information to the driver to program the pixel circuit, wherein the programming information is based at least in part on the received data input and the determined amount of compensation.

28. The display system according to claim 27, wherein the pixel circuit further includes a second switch transistor connecting the gate terminal of the driving transistor to a reference line.

29. The display system according to claim 28, wherein the first and second switch transistors are operated according to a common select line.

30. The display system according to claim 29, wherein the controller is further configured to apply a reference voltage on the reference line, during the programming cycle, such that the storage capacitor is charged according to the difference between the reference voltage and the voltage on the data line.

31. The display system according to claim 29, wherein the controller is further configured to apply a compensation voltage, on the reference line, during the programming cycle, wherein the compensation voltage is based on the determined amount of compensation.

32. The display system according to claim 27, further comprising a plurality of similar pixel circuits arranged in an array of rows and columns to form a display panel, and wherein the controller is configured to extract indications of aging degradation for each pixel circuit in the display panel, determine an amount of compensation for each pixel circuit in the display panel, and program each pixel circuit in the display panel according to the respective determined amounts of compensation.

33. The display system according to claim 27, wherein the light emitting device includes a light emitting diode.