Voltage programmed pixel circuit, display system and driving method thereof

1. A method of programming a pixel circuit including a driving section having a drive transistor and an emissive device and a programming section having a programming transistor, the method comprising:

applying from a data line a programming voltage to the programming transistor during a programming cycle;

the programming transistor converting the programming voltage to a corresponding programming current;

the programming current adjusting a gate-source voltage of the drive transistor; and

the driving section driving the emissive device with a drive current related to the programming current while the programming transistor is off, such that the drive current is independent of aging effects of the drive transistor and of the emissive device.

2. The method of claim 1 , wherein during the programming cycle, the programming transistor acts as a stable local reference transistor to adjust the programming current as a local current source.

3. The method of claim 1 , wherein during the programming cycle, a bias voltage is provided to a node in the programming section to cause a voltage at a node in the driving section to be related to the bias voltage, the programming information, a threshold voltage of the programming transistor, and a threshold voltage of the drive transistor.

4. The method of claim 3 , wherein during a driving cycle in which the driving section drives the emissive device immediately following the programming cycle, a voltage at the node in the driving section goes to a voltage of the emissive device while the gate-source voltage of the drive transistor is adjusted by the programming current.

5. The method of claim 1 , wherein the programming transistor is on for a small fraction of time during a frame and is off during the rest of the frame.

6. A method of programming a pixel circuit including a driving section having a drive transistor and an emissive device and a programming section having a programming transistor, a first terminal of the programming transistor coupled to a first terminal of the drive transistor, the method comprising, during a frame:

during a programming cycle:

applying a gate voltage to a gate of the drive transistor and a second terminal voltage to a second terminal of the drive transistor turning the drive transistor off; and

driving the programming transistor on with a first voltage difference across a gate of the programming transistor and a second terminal of the programming transistor having a magnitude equal to a predetermined programming voltage to charge a storage element coupled to the first terminal of the programming transistor with a driving voltage, and

during an operation cycle following the programming cycle:

applying the driving voltage across the gate of the drive transistor and the first terminal of the drive transistor to turn it on; and

driving the programming transistor off with a second voltage difference across the gate of the programming transistor and the second terminal of the programming transistor.

7. The method according to claim 6 wherein the emissive device has a first terminal coupled to the first terminal of the drive transistor and wherein,

during the programming cycle the emissive device remains off and during the operation cycle a current flows through the drive transistor according to the driving voltage turning on the emissive device.

8. The method of claim 7 wherein the storage element comprises a capacitor coupled between the first terminal of the drive transistor and the gate of the drive transistor.

9. The method of claim 8 wherein the driving voltage is substantially equal to the predefined programming voltage adjusted by a threshold voltage of the drive transistor.

10. The method of claim 9 wherein the emissive device is an organic light emitting diode (OLED) and wherein the driving voltage is independent of the operating voltage of the OLED V OLED .

11. The method of claim 10 , wherein the time duration of the programming cycle is a small fraction of the time duration of the operating cycle.