Pixel circuit and image display apparatus having the pixel circuit
A pixel circuit and an image display apparatus are provided making use of a hysteresis characteristics of a transistor for driving a display element. The pixel circuit comprises: a transistor providing both different first and second relations between a gate voltage value and a drain current value at a transition from off state to an on state, and from the on state transits to the off state respectively; a display element supplied as a drive current with a current controlled by the transistor; and a capacitor element connected to a gate electrode of the transistor. One of the first and second relations is utilized during a first period for setting the drive current to be supplied to the display element. And, the other of the first and second relations is utilized during a second period for supplying the drive current to the display element to effect light emission.
1. An image display apparatus comprising a pixel circuit, the pixel circuit comprising:
a transistor having hysteresis characteristics in which a relation between a gate voltage value and a drain current value at a transition from an off state to an on state and a relation between the gate voltage value and the drain current value at a transition from the on state to the off state are different;
a display element supplied a drive current controlled by said transistor; and
a capacitor element directly connected between a gate electrode of said transistor and a voltage line, wherein:
after a first period for setting a gate-source voltage of the transistor to set the drive current to be supplied for the display element to emit light, and before a second period for supplying the drive current for the display element to emit light,
the gate-source voltage of the transistor is controlled to be lower than a threshold voltage of the transistor of the first period in a case where the transistor has counter-clockwise hysteresis characteristics, and to be higher than the gate-source voltage of the transistor of the first period in a case where the transistor has clockwise hysteresis characteristics,
wherein, after the second period and before the first period of a subsequent frame the gate-source voltage of the transistor is controlled to be lower than the threshold voltage of the transistor in a case where the transistor has clockwise hysteresis characteristics, and the gate-source voltage of the transistor is controlled to be higher than the gate-source voltage of the transistor of the first period when the transistor has counter-clockwise hysteresis characteristics.
2. The image display apparatus according to claim 1 , wherein the gate-source voltage after the first period and before the second period is controlled by a change in voltage level of a wiring connected to the gate of the transistor via the capacitor.
3. The image display apparatus according to claim 1 , wherein said display element in said pixel circuit is an OLED element.
4. The image display apparatus according to claim 1 , wherein a channel layer of said transistor constituting the pixel circuit is made of amorphous silicon, amorphous silicon oxide material, or organic semiconductor material.