Stable driving scheme for active matrix displays
A method and system for operating a pixel array having at least one pixel circuit is provided. The method includes repeating an operation cycle defining a frame period for a pixel circuit, including at each frame period, programming the pixel circuit, driving the pixel circuit, and relaxing a stress effect on the pixel circuit, prior to a next frame period. The system includes a pixel array including a plurality of pixel circuits and a plurality of lines for operation of the plurality of pixel circuits. Each of the pixel circuits includes a light emitting device, a storage capacitor, and a drive circuit connected to the light emitting device and the storage capacitor. The system includes a drive for operating the plurality of lines to repeat an operation cycle having a frame period so that each of the operation cycle comprises a programming cycle, a driving cycle and a relaxing cycle for relaxing a stress on a pixel circuit, prior to a next frame period.
1. A method of operating a pixel array having pixel circuits, each pixel circuit including a drive transistor and a light emitting device, and driven by repeating an operation cycle defining a frame period for each pixel circuit, the method comprising:
providing first voltages to a first pixel circuit during a programming operation cycle of a frame period of the first pixel circuit; and
providing second voltages to a second pixel circuit while said providing said first voltages to said first pixel circuit during a relaxing operation cycle of a frame period of the second pixel circuit, said second voltages relaxing said second pixel without resetting said second pixel.
2. The method of claim 1 , wherein the first voltages and the second voltages each comprise a first voltage provided via a signal line coupled to the first pixel circuit and the second pixel circuit.
3. The method of claim 2 , wherein the first voltages comprise a first supply voltage used to drive the light emitting device of the first pixel circuit, wherein the second voltages comprise a second supply voltage used to drive the light emitting device of the second pixel circuit, the first supply voltage different from the second supply voltage, and wherein a polarity of the first supply voltage is opposite in polarity to that of the first voltage.
4. The method of claim 2 , further comprising:
providing a second voltage to the first pixel circuit over the signal line during a relaxing operation cycle of the frame period of the first pixel circuit; and
deselecting the second pixel circuit during the relaxing operation cycle of the frame period of the first pixel circuit isolating the second pixel circuit from the second voltage on the signal line.
5. The method of claim 1 , further comprising:
during said providing said first voltages to the first pixel circuit and said providing said second voltages to the second pixel circuit, selecting the first pixel circuit and selecting the second pixel circuit.
6. The method of claim 5 , wherein the first voltages comprise a first voltage provided over a signal line coupled to the first pixel circuit and the second pixel circuit, the first voltage smaller than V T0 +V OLED0 where V T0 is a threshold voltage of the drive transistor of the first pixel circuit in an unstressed state and V OLED0 is an on voltage of the light-emitting device of the first pixel circuit in an unstressed state.
7. The method of claim 1 , wherein the first voltages are sufficient to cause, during the programming operation cycle of the frame period of the first pixel circuit, the drive transistor of the first pixel circuit to turn on and the light emitting device of the first pixel circuit to remain off.
8. The method of claim 1 , wherein the second voltages are sufficient to cause, during the relaxing operation cycle of the frame period of the second pixel circuit, the drive transistor of the second pixel circuit to turn off and the light emitting device of the second pixel circuit to turn off.
9. The method of claim 1 , wherein the second voltages are sufficient to cause, during the relaxing operation cycle of the frame period of the second pixel circuit, biasing of the transistor of the second pixel circuit with reversed polarity.
10. The method of claim 1 , further comprising:
deselecting the second pixel circuit at the end of the relaxing operation cycle of the frame period of the second pixel circuit.
11. A display system comprising:
a pixel array having pixel circuits, each pixel circuit including a drive transistor and a light emitting device;
a driver coupled to the pixel circuits and for driving the pixel circuits by repeating an operation cycle defining a frame period for each pixel circuit;
and a controller coupled to the driver, the controller operable to:
provide first voltages to a first pixel circuit during a programming operation cycle of a frame period of the first pixel circuit; and
provide second voltages to a second pixel circuit while said providing said first voltages to said first pixel circuit and during a relaxing operation cycle of a frame period of the second pixel circuit, said second voltages relaxing said second pixel without resetting said second pixel.
12. The display system of claim 11 , further comprising:
a signal line coupled to the first pixel circuit and the second pixel circuit, the first voltages and the second voltages each comprise a first voltage provided via the signal line to the first pixel circuit and the second pixel circuit.
13. The display system of claim 12 , wherein the first voltages comprise a first supply voltage used to drive the light emitting device of the first pixel circuit, wherein the second voltages comprise a second supply voltage used to drive the light emitting device of the second pixel circuit, the first supply voltage different from the second supply voltage, and wherein a polarity of the first supply voltage is opposite in polarity to that of the first voltage.
14. The display system of claim 12 , wherein the controller is further operable to:
provide a second voltage to the first pixel circuit over the signal line during a relaxing operation cycle of the frame period of the first pixel circuit; and
deselect the second pixel circuit during the relaxing operation cycle of the frame period of the first pixel circuit isolating the second pixel circuit from the second voltage on the signal line.
15. The display system of claim 11 , wherein the controller is further operable to:
during providing said first voltages to the first pixel circuit and providing said second voltages to the second pixel circuit, select the first pixel circuit and select the second pixel circuit.
16. The display system of claim 15 , wherein the first voltages comprise a first voltage provided over a signal line coupled to the first pixel circuit and the second pixel circuit, the first voltage smaller than V T0 +V OLEP0 where V T0 is a threshold voltage of the drive transistor of the first pixel circuit in an unstressed state and V OLED0 is an on voltage of the light-emitting device of the first pixel circuit in an unstressed state.
17. The display system of claim 11 , wherein the first voltages are sufficient to cause, during the programming operation cycle of the frame period of the first pixel circuit, the drive transistor of the first pixel circuit to turn on and the light emitting device of the first pixel circuit to remain off.
18. The display system of claim 11 , wherein the second voltages are sufficient to cause, during the relaxing operation cycle of the frame period of the second pixel circuit, the drive transistor of the second pixel circuit to turn off and the light emitting device of the second pixel circuit to turn off.
19. The display system of claim 11 , wherein the second voltages are sufficient to cause, during the relaxing operation cycle of the frame period of the second pixel circuit, biasing of the transistor of the second pixel circuit with reversed polarity.
20. The display system of claim 11 , wherein the controller is further operable to:
deselect the second pixel circuit at the end of the relaxing operation cycle of the frame period of the second pixel circuit.