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 arranged in rows and columns, 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:
setting a data line of a first column at a first voltage;
providing the first voltage to a first pixel circuit in the first column during a first operation cycle of a frame period of the first pixel circuit by activating a first select line coupled to the first pixel circuit; and
providing the first voltage to a second pixel circuit in the first column during a second operation cycle of a frame period of the second pixel circuit which overlaps in time the first operation cycle of the frame period of the first pixel by activating a second select line coupled to the second pixel circuit.
2. The method of claim 1 , wherein the first operation cycle comprises a first programming operation cycle and wherein the second operation cycle comprises a first relaxing operation cycle.
3. The method of claim 1 , wherein the first voltage is sufficient to cause, during the first 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 to remain off.
4. The method of claim 1 , wherein the first voltage is sufficient to cause, during the second 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 to turn off.
5. The method of claim 1 , wherein the first voltage is sufficient to cause, during the second operation cycle of the frame period of the second pixel circuit, negative biasing of the transistor of the second pixel circuit.
6. The method of claim 1 , further comprising:
during the first operation cycle of the frame period of the first pixel circuit,
adjusting a first controllable power supply line for the first pixel circuit to a first supply voltage, the first supply voltage opposite in polarity to that of the first voltage; and
during the second operation cycle of the frame period of the second pixel circuit, adjusting a second controllable power supply line for the second pixel circuit to a second supply voltage, the second supply voltage corresponding to a voltage used to drive the light emitting device of the second pixel circuit.
7. The method of claim 1 , further comprising:
setting the data line at a second voltage during a second operation cycle of the frame period of the first pixel circuit, the second voltage comprising at least a programming voltage for the first pixel circuit, and
ensuring the second select line is deactivated during a second operation cycle of the frame period of the first pixel circuit isolating the second pixel circuit from the second voltage.
8. The method of claim 1 , further comprising:
deactivating the second select line at the end of the second operation cycle of the frame period of the second pixel circuit.
9. The method of claim 1 , wherein the first voltage is smaller than VT0+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 and on voltage of the light-emitting device of the first pixel circuit in an unstressed state.