Systems and methods for aging compensation in AMOLED displays
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.
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 comprising:
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 coupled between a first terminal of the storage capacitor and at least one of the light emitting device and the driving transistor, and for disconnecting said first terminal from said at least one of the driving transistor and the light emitting device during the programming cycle,
a driver for programming the pixel circuit via a data line by charging the storage capacitor according to the programming information; and
a controller for operating the driver and configured to:
receive a data input indicative of an amount of luminance to be emitted from the light emitting device; 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.
2. The system according to claim 1 , wherein the storage capacitor and the emission control transistor are coupled in series directly to a node between the driving transistor and the light emitting device.
3. The system according to claim 1 , wherein the emission control transistor is further for connecting said first terminal of the storage capacitor and said at least one of the light emitting device and the driving transistor, such that current is conveyed through the driving transistor and the light emitting device, during an emission cycle, according to voltage charged on the storage capacitor.
4. The system according to claim 1 , wherein the emission control transistor is coupled between the first terminal of the storage capacitor and the light emitting device.
5. The system according to claim 1 , wherein the emission control transistor is coupled between the first terminal of the storage capacitor and the driving transistor.
6. The system according to claim 1 , further comprising a monitor for extracting a voltage or a current indicative of degradation of the pixel circuit during a monitoring cycle, wherein the pixel circuit further comprises at least one switch transistor for connecting a current path through the driving transistor to the monitor during the monitoring cycle, and wherein the controller is further for operating the monitor and is further configured to:
receive an indication of the amount of degradation from the monitor; and
determine an amount of compensation to provide to the pixel circuit based on the amount of degradation;
wherein the programming information further is based at least in part on the determined amount of compensation.
7. The pixel circuit according to claim 6 , further comprising:
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; 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 the current or voltage indicative of the degradation of the pixel circuit to the monitor, during the monitoring cycle.
8. The system according to claim 1 , wherein the first terminal said at least one of the driving transistor and the light emitting device are disconnected during the programming cycle such that a perturbation of the charging of the storage capacitor during the programming cycle by at least one of the driving transistor and the light emitting device is prevented.
9. The system according to claim 8 , wherein perturbation of the charging of the storage capacitor during the programming cycle caused by a capacitance of the light emitting device is prevented, and the pixel circuit is programmed independent of the capacitance of the light emitting device.
10. The system according to claim 8 , wherein perturbation of the charging of the storage capacitor during the programming cycle caused by current generated by the driving transistor is prevented.
11. The system according to claim 10 , wherein perturbation of the charging of the storage capacitor during the programming cycle caused by a shift in voltage applied to a terminal of the storage device due to current generated by the driving transistor flowing through a further circuit element is prevented.
12. The system according to claim 11 , wherein the further circuit element comprises a switch transistor and the pixel circuit is programmed independent of a resistance of the switch transistor.
13. 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; and
an emission control transistor coupled between a first terminal of the storage capacitor and at least one of the light emitting device and the driving transistor, and for disconnecting said first terminal from said at least one of the driving transistor and the light emitting device during the programming cycle.
14. The pixel circuit according to claim 13 , wherein the storage capacitor and the emission control transistor are coupled in series directly to a node between the driving transistor and the light emitting device.
15. The pixel circuit according to claim 13 , wherein the emission control transistor is further for connecting said first terminal of the storage capacitor and said at least one of the light emitting device and the driving transistor, such that current is conveyed through the driving transistor and the light emitting device, during an emission cycle, according to voltage charged on the storage capacitor.
16. The pixel circuit according to claim 13 , wherein the emission control transistor is coupled between the first terminal of the storage capacitor and the light emitting device.
17. The pixel circuit according to claim 13 , wherein the emission control transistor is coupled between the first terminal of the storage capacitor and the driving transistor.
18. The pixel circuit according to claim 13 , further comprising at least one switch transistor for connecting a current path through the driving transistor to a monitor for extracting a voltage or a current indicative of degradation of the pixel circuit, during a monitoring cycle.
19. The pixel circuit according to claim 18 , further comprising:
a data switch transistor, operated according to a select line, for coupling, during the programming cycle, a data line to a terminal of the storage capacitor; 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 the current or voltage indicative of the degradation of the pixel circuit to the monitor, during the monitoring cycle.
20. The pixel circuit according to claim 13 , wherein the first terminal said at least one of the driving transistor and the light emitting device are disconnected during the programming cycle such that a perturbation of the charging of the storage capacitor during the programming cycle by at least one of the driving transistor and the light emitting device is prevented.
21. The pixel circuit according to claim 20 , wherein perturbation of the charging of the storage capacitor during the programming cycle caused by a capacitance of the light emitting device is prevented, and the pixel circuit is programmed independent of the capacitance of the light emitting device.
22. The pixel circuit according to claim 20 , wherein perturbation of the charging of the storage capacitor during the programming cycle caused by current generated by the driving transistor is prevented.
23. The pixel circuit according to claim 22 , wherein perturbation of the charging of the storage capacitor during the programming cycle caused by a shift in voltage applied to a terminal of the storage device due to current generated by the driving transistor flowing through a further circuit element is prevented.
24. The pixel circuit according to claim 23 , wherein the further circuit element comprises a switch transistor and the pixel circuit is programmed independent of a resistance of the switch transistor.