Light emitting device and driving method of the same
The invention provides a light emitting device and an element substrate in which a luminance variation of light emitting elements among pixels due to variation in characteristics of driving transistors can be suppressed even without suppressing the off-current of a switching transistor low or increasing the capacitance of a capacitor. A gate of a first transistor is connected to a first scan line, and a gate of a second transistor is connected to a second scan line. A connection between a signal line and a gate of a third transistor is controlled by the first transistor. The second transistor and the third transistor are connected in series between a pixel electrode of a light emitting element and a power supply line. The signal line, the second scan line and the power supply line are disposed in parallel, while the first scan line is crossed with the signal line, the second scan line and the power supply line.
1. A driving method of a light emitting device comprising a pixel comprising a first transistor, a second transistor, a third transistor and a light emitting element,
wherein the light emitting element comprises a pixel electrode, a counter electrode, and an electroluminescent layer formed between the pixel electrode and the counter electrode,
wherein the second transistor and the third transistor are electrically connected in series between a first power supply line and the pixel electrode,
wherein a gate electrode of the first transistor is electrically connected to a scan line,
wherein a gate electrode of the second transistor is electrically connected to a second power supply line having a second potential, and
wherein a gate electrode of the third transistor is electrically connected to one of a source electrode and a drain electrode of the first transistor,
the driving method comprising:
applying a first potential to the gate electrode of the third transistor by turning ON the first transistor by selecting the scan line, wherein the second transistor is ON when the first transistor is ON;
making the counter electrode into a floating state while the first potential is applied to the gate electrode of the third transistor;
turning OFF the first transistor; and
applying a third potential to the counter electrode so that a current flows in the light emitting element,
wherein the first transistor operates in a linear region,
wherein the second transistor operates in a saturation region,
wherein the third transistor operates in a linear region,
wherein the second potential is a fixed potential,
wherein an amount of the current is controlled by the second transistor, and
wherein the current does not flow in the light emitting element while the first transistor and the second transistor are ON.
2. The driving method of a light emitting device according to claim 1 , wherein the light emitting device further comprises a fourth transistor between the second transistor and the third transistor.
3. The driving method of a light emitting device according to claim 1 , wherein the current supplied to the light emitting element is a constant current.
4. A driving method of a light emitting device comprising a first transistor, a second transistor, a third transistor and a light emitting element,
wherein the light emitting element comprises a pixel electrode, a counter electrode, and an electroluminescent layer formed between the pixel electrode and the counter electrode,
wherein the second transistor and the third transistor are electrically connected in series between a first power supply line and the pixel electrode,
wherein a gate electrode of the third transistor is electrically connected to one of a source electrode and a drain electrode of the first transistor, and
wherein a gate electrode of the second transistor is electrically connected to a second power supply line, the driving method comprising:
applying a first potential to the gate electrode of the third transistor by turning ON the first transistor;
applying a third potential of the first power supply line to the counter electrode while the first potential is applied to the gate electrode of the third transistor;
turning OFF the first transistor; and
applying a fourth potential to the counter electrode so that a current flows in the light emitting element,
wherein the first transistor operates in a linear region,
wherein the second transistor operates in a saturation region,
wherein the third transistor operates in a linear region,
wherein a second potential of the second power supply line is fixed,
wherein an amount of the current is controlled by the second transistor, and
wherein the current does not flow in the light emitting element while the first transistor and the second transistor are ON.
5. The driving method of a light emitting device according to claim 4 , wherein the first transistor operates in a linear region.
6. The driving method of a light emitting device according to claim 4 , wherein the light emitting device further comprises a fourth transistor between the second transistor and the third transistor.
7. The driving method of a light emitting device according to claim 4 , wherein the third potential of the first power supply line is a constant potential.
8. A driving method of a light emitting device comprising a pixel comprising a first transistor, a second transistor, a third transistor and a light emitting element,
wherein the light emitting element comprises a pixel electrode, a counter electrode, and an electroluminescent layer formed between the pixel electrode and the counter electrode,
wherein the second transistor and the third transistor are electrically connected in series between a first power supply line and the pixel electrode,
wherein a gate electrode of the first transistor is electrically connected to a scan line,
wherein a gate electrode of the second transistor is electrically connected to a second power supply line having a second potential,
wherein a gate electrode of the third transistor is electrically connected to one of a source electrode and a drain electrode of the first transistor, and
wherein the scan line crosses the second power supply line,
the driving method comprising:
applying a first potential to the gate electrode of the third transistor by turning ON the first transistor by selecting the scan line, wherein the second transistor is ON when the first transistor is ON;
making the counter electrode into a floating state while the first potential is applied to the gate electrode of the third transistor;
turning OFF the first transistor; and
applying a third potential to the counter electrode so that a current flows in the light emitting element,
wherein the first transistor operates in a linear region,
wherein the second transistor operates in a saturation region,
wherein the third transistor operates in a linear region,
wherein the second potential is a fixed potential,
wherein an amount of the current is controlled by the second transistor, and
wherein the current does not flow in the light emitting element while the first transistor and the second transistor are ON.
9. The driving method of a light emitting device according to claim 8 , wherein the current supplied to the light emitting element is a constant current .
10. A driving method of a light emitting device comprising a pixel comprising a first transistor, a second transistor, a third transistor, and a light emitting element,
wherein the light emitting element comprises a pixel electrode, a counter electrode, and an electroluminescent layer formed between the pixel electrode and the counter electrode,
wherein the second transistor and the third transistor are electrically connected in series between a first power supply line and the pixel electrode,
wherein a gate electrode of the first transistor is electrically connected to a scan line,
wherein a gate electrode of the second transistor is electrically connected to a second power supply line, and
wherein a gate electrode of the third transistor is electrically connected to one of a source electrode and a drain electrode of the first transistor,
the driving method comprising:
applying a first potential to the gate electrode of the third transistor by turning ON the first transistor by selecting the scan line, wherein the second transistor is ON while the first transistor is ON;
making the counter electrode into a floating state while the first potential is applied to the gate electrode of the third transistor;
turning OFF the first transistor; and
applying a third potential to the counter electrode so that a current flows in the light emitting element,
wherein the second power supply line is configured to be supplied with a second potential which is a fixed potential,
wherein the current does not flow in the light emitting element while the first transistor and the second transistor are ON,
wherein the first transistor operates in a linear region,
wherein the second transistor operates in a saturation region, and
wherein the third transistor operates in a linear region.