Pixel circuits for AMOLED displays
A system for controlling a display in which each pixel circuit comprises a light-emitting device, a drive transistor, a storage capacitor, a reference voltage source, and a programming voltage source. The storage capacitor stores a voltage equal to the difference between the reference voltage and the programming voltage, and a controller supplies a programming voltage that is a calibrated voltage for a known target current, reads the actual current passing through the drive transistor to a monitor line, turns off the light emitting device while modifying the calibrated voltage to make the current supplied through the drive transistor substantially the same as the target current, modifies the calibrated voltage to make the current supplied through the drive transistor substantially the same as the target current, and determines a current corresponding to the modified calibrated voltage based on predetermined current-voltage characteristics of the drive transistor.
1. A display system comprising:
a supply voltage source;
a plurality of pixels, including at least one pixel circuit including:
a light-emitting device,
a drive transistor for driving current through the light-emitting device according to a driving voltage across the drive transistor during an emission cycle, and
a storage capacitor having a first terminal and a second terminal and for storing a voltage to be applied to the drive transistor during the emission cycle; and
a controller configured to:
during a first operation cycle, couple the storage capacitor to the supply voltage source; and
during a second operation cycle different from the first operation cycle, decouple the storage capacitor from the supply voltage source.
2. The display system of claim 1 , wherein the first operation cycle occurs prior to the second operation cycle.
3. The display system of claim 1 , wherein the first operation cycle occurs subsequent to the second operation cycle.
4. The display system of claim 1 , wherein the controller is further configured to:
during the first operation cycle, decouple one of the first and second terminals of the storage capacitor from any voltage source allowing its voltage to float; and
during the second operation cycle, couple the first and second terminals of the storage capacitor to two different voltage sources.
5. The display system of claim 1 , wherein the controller is further configured to:
during the first operation cycle, couple the first and second terminals of the storage capacitor to two different voltage sources; and
during the second operation cycle, decouple one of the first and second terminals of the storage capacitor from any voltage source allowing its voltage to float.
6. The display system of claim 4 , wherein the first operation cycle occurs subsequent to the second operation cycle, wherein the controller is further configured to:
during the first operation cycle, couple the other of the first and second terminals of the storage capacitor to the supply voltage source; and
during the second operation cycle, couple the first terminal of the storage capacitor to a data voltage source via a data line while coupling the second terminal of the storage capacitor to a predetermined voltage source.
7. The display system of claim 6 , wherein the predetermined voltage source is a reference voltage source.
8. The display system of claim 5 , wherein the first operation cycle occurs prior to the second operation cycle, wherein the controller is further configured to:
during the first operation cycle, couple the first terminal of the storage capacitor to the supply voltage source while coupling the second terminal of the storage capacitor to a data voltage source via a data line; and
during the second operation cycle, couple the other of the first and second terminals of the storage capacitor to a predetermined voltage source.
9. The display system of claim 8 , wherein the predetermined voltage source is a reset voltage source.
10. A display system comprising:
a supply voltage source;
a plurality of pixels, each pixel comprising a pixel circuit including:
a light-emitting device,
a drive transistor for, during an emission cycle, driving current through the light-emitting device according to a driving voltage across the drive transistor,
a storage capacitor for storing a voltage to be applied to the drive transistor during the emission cycle; and
a controller configured to:
couple the supply voltage source to the storage capacitor and decouple the supply voltage source from the storage capacitor such that the driving current is independent of changes in a supply voltage of the supply voltage source.
11. A method of controlling a display system including a supply voltage source and a plurality of pixels including at least one pixel circuit including a light-emitting device, a drive transistor for driving current through the light-emitting device according to a driving voltage across the drive transistor during an emission cycle, and a storage capacitor having a first terminal and a second terminal and for storing a voltage to be applied to the drive transistor during the emission cycle, the method comprising:
during a first operation cycle, coupling the storage capacitor to the supply voltage source; and
during a second operation cycle different from the first operation cycle, decoupling the storage capacitor from the supply voltage source.
12. The method of claim 11 , wherein the first operation cycle occurs prior to the second operation cycle.
13. The method of claim 11 , wherein the first operation cycle occurs subsequent to the second operation cycle.
14. The method of claim 11 , comprising:
during the first operation cycle, decoupling one of the first and second terminals of the storage capacitor from any voltage source allowing its voltage to float; and
during the second operation cycle, coupling the first and second terminals of the storage capacitor to two different voltage sources.
15. The method of claim 11 , comprising:
during the first operation cycle, coupling the first and second terminals of the storage capacitor to two different voltage sources; and
during the second operation cycle, decoupling one of the first and second terminals of the storage capacitor from any voltage source allowing its voltage to float.
16. The method of claim 14 , wherein the first operation cycle occurs subsequent to the second operation cycle, the method comprising:
during the first operation cycle, coupling the other of the first and second terminals of the storage capacitor to the supply voltage source; and
during the second operation cycle, coupling the first terminal of the storage capacitor to a data voltage source via a data line while coupling the second terminal of the storage capacitor to a predetermined voltage source.
17. The method of claim 16 , wherein the predetermined voltage source is a reference voltage source.
18. The method of claim 15 , wherein the first operation cycle occurs prior to the second operation cycle, the method comprising:
during the first operation cycle, coupling the first terminal of the storage capacitor to the supply voltage source while coupling the second terminal of the storage capacitor to a data voltage source via a data line; and
during the second operation cycle, coupling the other of the first and second terminals of the storage capacitor to a predetermined voltage source.
19. The method of claim 18 , wherein the predetermined voltage source is a reset voltage source.
20. A method of controlling a display system including a supply voltage source and a plurality of pixels including at least one pixel circuit including a light-emitting device, a drive transistor for, during an emission cycle, driving current through the light-emitting device according to a driving voltage across the drive transistor, and a storage capacitor for storing a voltage to be applied to the drive transistor during the emission cycle, the method comprising:
coupling the supply voltage source to the storage capacitor and decoupling the supply voltage source from the storage capacitor such that the driving current is independent of changes in a supply voltage of the supply voltage source.