OLED luminance degradation compensation
A system and method are disclosed for determining a pixel capacitance. The pixel capacitance is correlated to a pixel age to determine a current correction factor used for compensating the pixel drive current to account for luminance degradation of the pixel that results from the pixel aging.
1. A method of driving a pixel, the method comprising:
electrically coupling the pixel to read block circuitry;
taking at least one reading from the pixel with the read block circuitry;
determining a capacitance of an electroluminescent device of the pixel with use of the at least one reading from the pixel; and
driving the pixel based on the determined capacitance and a relationship between an aging of the pixel and the capacitance of the electroluminescent device.
2. The method as claimed in claim 1 , wherein driving the pixel based on the determined capacitance and the relationship between the aging of the pixel and the capacitance of the electroluminescent device comprises:
compensating a drive current for the pixel based on the determined capacitance and the relationship between the aging of the pixel and the capacitance of the electroluminescent device generating a compensated drive current; and
driving the pixel with the compensated drive current.
3. The method as claimed in claim 2 , wherein compensating the drive current for the pixel based on the determined capacitance and the relationship between the aging of the pixel and the capacitance of the electroluminescent device comprises:
correlating the determined capacitance of the pixel to a current correlation factor for the pixel; and
compensating the drive current according to the current correlation factor for the pixel.
4. The method as claimed in claim 3 , wherein the current correlation factor is an absolute amount of current to be added to the drive current to generate the compensated drive current.
5. The method as claimed in claim 3 , wherein the current correlation factor is a multiplier by which the driver current is multiplied to generate the compensated drive current.
6. The method as claimed in claim 3 , wherein the current correlation factor is retrieved from a lookup table that correlates desired luminance values with compensated driving currents, the lookup table being stored in a memory device.
7. A method of driving a pixel, the method comprising:
electrically coupling an electroluminescent device of the pixel to a read capacitor and charging the capacitance of the electroluminescent device with charge from the read capacitor;
determining the capacitance of the electroluminescent device from a change in charge stored in the read capacitor; and
driving the pixel based on said determined capacitance.
8. The method as claimed in claim 7 , wherein determining the capacitance of the electroluminescent device from a change in charge stored in the read capacitor comprises:
measuring a change in voltage across the read capacitor; and
determining the change in charge stored in the read capacitor from the change of voltage across the read capacitor.
9. A method of compensating a drive current for a pixel, the method comprising:
electrically coupling the pixel to read block circuitry;
taking at least one reading from the pixel with the read block circuitry;
determining a capacitance of an electroluminescent device of the pixel with use of the at least one reading from the pixel; and
generating a compensated drive current by compensating a drive current for the pixel based on the determined capacitance and a relationship between an aging of the pixel and the capacitance of the electroluminescent device.
10. The method as claimed in claim 9 , wherein compensating the drive current for the pixel based on the determined capacitance and the relationship between the aging of the pixel and the capacitance of the electroluminescent device comprises:
correlating the determined capacitance of the pixel to a current correlation factor for the pixel; and
compensating the drive current according to the current correlation factor for the pixel.
11. The method as claimed in claim 10 , wherein the current correlation factor is an absolute amount of current to be added to the drive current to generate the compensated drive current.
12. The method as claimed in claim 10 , wherein the current correlation factor is a multiplier by which the driver current is multiplied to generate the compensated drive current.
13. The method as claimed in claim 10 , wherein the current correlation factor is retrieved from a lookup table that correlates desired luminance values with compensated driving currents, the lookup table being stored in a memory device.
14. A method of compensating a drive current for a pixel, the method comprising:
electrically coupling an electroluminescent device of the pixel to a read capacitor and charging the capacitance of the electroluminescent device with charge from the read capacitor;
determining the capacitance of the electroluminescent device from a change in charge stored in the read capacitor and
generating a compensated drive current by compensating a drive current for the pixel based on the determined capacitance.
15. The method as claimed in claim 14 , wherein determining the capacitance of the electroluminescent device from a change in charge stored in the read capacitor comprises:
measuring a change in voltage across the read capacitor; and
determining the change in charge stored in the read capacitor from the change in voltage across the read capacitor.
16. A method of determining a capacitance of an electroluminescent device of a pixel, the method comprising:
electrically coupling the electroluminescent device to a read capacitor and charging the capacitance of the electroluminescent device with charge from the read capacitor; and
determining the capacitance of the electroluminescent device from a change in charge stored in the read capacitor.
17. The method as claimed in claim 16 , wherein determining the capacitance of the electroluminescent device from a change in charge stored in the read capacitor comprises:
measuring a change in voltage across the read capacitor; and
determining the change in charge stored in the read capacitor from the change in voltage across the read capacitor.
18. The method as claimed in claim 17 , further comprising, prior to determining the capacitance of the electroluminescent device from the change in the charge stored in the read capacitor:
charging a parasitic capacitance of a read line coupling the read capacitor and the electroluminescent device such that substantially none of the change in the charge stored on the read capacitor corresponds to a change in a charge stored by the parasitic capacitance.
19. The method claimed in claim 18 , wherein charging the parasitic capacitance comprises charging the parasitic capacitance to a voltage equal to the voltage of the read capacitor.
20. The method as claimed in claim 17 , further comprising, prior to determining the capacitance of the electroluminescent device from the change in the charge stored in the read capacitor:
charging a parasitic capacitance of a read circuit in which the read capacitor is situated such that substantially none of the change in the charge stored on the read capacitor corresponds to a change in a charge stored by the parasitic capacitance.
21. The method claimed in claim 20 , wherein charging the parasitic capacitance comprises charging the parasitic capacitance to a voltage equal to the voltage of the read capacitor.