Voltage programmed pixel circuit, display system and driving method thereof
A voltage programmed pixel circuit, display system having the pixel circuit and driving method thereof is provided. The pixel circuit includes a light emitting device, a driving transistor connected to the light emitting device and a programming circuit. The programming circuit adjusts a pixel current during a programming cycle of the pixel circuit.
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:
the programming transistor converting its gate-source voltage to a programming current, the programming transistor operating as a stable local reference transistor to supply the programming current as a local current source to the drive transistor;
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 and causing the emissive device to emit light according to at least the programming current while the programming transistor remains off, such that the drive current is independent of aging effects of the drive transistor and of the emissive device,
wherein the programming transistor is on for a small fraction of time during a frame and is off during the rest of the frame including the entire time the driving section is driving the emissive device, and wherein the emissive device is off during a programming cycle of the pixel circuit.
2. The method of claim 1 , wherein during the programming cycle in which programming information is transferred to the programming section for causing the emissive device to emit light according to at least the programming information, 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.
3. The method of claim 2 , 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.