Display device and driving method of the same
View Patent ↗A problem in that a light emitting element slightly emits light is solved by an off current of a thin film transistor connected in series to the light emitting element, thereby a display device which can perform a clear display by increasing contrast, and a driving method thereof are provided. When the thin film transistor connected in series to the light emitting element is turned off, a charge held in the capacitance of the light emitting element itself is discharged. Even when an off current is generated at the thin film transistor connected in series to the light emitting element, this off current charges this capacitance until the capacitance of the light emitting element itself holds a predetermined voltage again. Accordingly, the off current of the thin film transistor does not contribute to light emission. In this manner, a slight light emission of the light emitting element can be reduced.
1. A display device comprising:
a pixel including a first thin film transistor, a second thin film transistor, a third thin film transistor, a fourth thin film transistor, a first capacitor, a second capacitor and a light emitting element;
a signal line;
a first power source line;
a second power source line;
a third power source line,
wherein one of a source and a drain of the first thin film transistor is electrically connected to the signal line and the other of the source and the drain of the first thin film transistor is electrically connected to a gate of the second thin film transistor,
wherein one of a source and a drain of the second thin film transistor is electrically connected to the first power source line and the other of the source and the drain of the second thin film transistor is electrically connected to a first electrode of the light emitting element,
wherein a second electrode of the light emitting element is electrically connected to the second power source line,
wherein one of a source and a drain of the third thin film transistor is electrically connected to the first electrode of the light emitting element and the other of the third thin film transistor is directly connected to the third power source line,
wherein the first capacitor is electrically connected in parallel to the light emitting element,
wherein the second capacitor is located between one of the source and the drain of the second thin film transistor and the gate of the second thin film transistor,
wherein the fourth thin film transistor is electrically connected in parallel to the second capacitor,
wherein a gate of the third thin film transistor is electrically connected to a gate of the fourth thin film transistor, and
wherein a potential of the second power source line is lower than that of the third power source line.
2. The display device according to claim 1 ,
wherein the first thin film transistor has an active layer formed of a polycrystalline semiconductor.
3. A electronic device, using the display device according to claim 1 .
4. A display device comprising:
a pixel including a first thin film transistor, a second thin film transistor, a third thin film transistor, a first capacitor, a second capacitor, and a light emitting element;
a first power source line;
a second power source line; and
a third power source line,
wherein one of a source and a drain of the first thin film transistor is electrically connected to the first power source line and the other of the source and the drain of the first thin film transistor is electrically connected to a first electrode of the light emitting element;
wherein a second electrode of the light emitting element is electrically connected to the second power source line;
wherein one of a source and a drain of the second thin film transistor is electrically connected to the first electrode of the light emitting element and the other of the source and the drain of the second thin film transistor is directly connected to the third power source line,
wherein the first capacitor is located between one of the source and the drain of the first thin film transistor and a gate of the first thin film transistor,
wherein the third thin film transistor is electrically connected in parallel to the first capacitor,
wherein a gate of the second thin film transistor is electrically connected to a gate of the third thin film transistor,
wherein the second capacitor is electrically connected in parallel to the light emitting element, and
wherein a potential of the second power source line is lower than that of the third power source line.
5. The display device according to claim 4 ,
wherein the first thin film transistor is turned on when the second thin film transistor is turned off, and
wherein the first thin film transistor is turned off when the second thin film transistor is turned on.
6. The display device according to claim 4 ,
wherein a first electrode of the second capacitor is electrically connected to the first electrode of the light emitting element, and
wherein a second electrode of the second capacitor is electrically connected to the second power source line.
7. The display device according to claim 4 ,
wherein the first thin film transistor has an active layer formed of a polycrystalline semiconductor.
8. A electronic device, using the display device according to claim 4 .
9. A driving method of a display device comprising:
a pixel including a first thin film transistor, a second thin film transistor, a third thin film transistor, a capacitor, a first capacitor, and a light emitting element;
a first power source line;
a second power source line; and
a third power source line,
wherein the light emitting element includes a first electrode and a second electrode;
wherein one of a source and a drain of the first thin film transistor is electrically connected to the first power source line and the other of the source and the drain of the first thin film transistor is electrically connected to a first electrode of the light emitting element,
wherein the second electrode of the light emitting element is electrically connected to the second power source line,
wherein one of a source and a drain of the second thin film transistor is electrically connected to the first electrode and the other of the source and the drain of the second thin film transistor is directly connected to the third power source line,
wherein the capacitor is located between one of the source and a drain of the first thin film transistor and a gate of the first thin film transistor,
wherein a gate of the second thin film transistor is electrically connected to a gate of the third thin film transistor,
wherein the third thin film transistor is electrically connected in parallel to the capacitor, the driving method comprising:
applying a first potential to the first electrode of the light emitting element by turning on the first thin film transistor while a second potential is applied to the second potential to the second electrode of the light emitting element through the second power source line;
turning off the first thin film transistor and turning on the second thin film transistor and the third thin film transistor; and
applying a third potential to the first electrode of the light emitting element through the third power source line after turning on the second thin film transistor and the third thin film transistor, and
wherein the third potential is equal to or higher than the second potential and a voltage applied between the first electrode and the second electrode of the light emitting element is lower than a threshold voltage of the light emitting element, and
wherein the first capacitor is electrically connected in parallel to the light emitting element.
10. The driving method of a display device, according to claim 9 ,
wherein a first electrode of the first capacitor is electrically connected to the first electrode of the light emitting element, and
wherein a second electrode of the first capacitor is electrically connected to the second power source line.
11. The driving method of a display device, according to claim 9 ,
wherein the first thin film transistor has an active layer formed of a polycrystalline semiconductor.
12. The driving method of a display device, according to claim 9 ,
wherein a gray scale is displayed by controlling the time in which the light emitting element emits light in one frame period.
13. The display device, according to claim 1 ,
wherein the first to fourth thin film transistors have the same conductivity type.
14. The display device, according to claim 4 ,
wherein the first to third thin film transistors have the same conductivity type.
15. The driving method of a display device, according to claim 9 ,
wherein the first to third thin film transistors have the same conductivity type.
16. A display device comprising:
a pixel including a first thin film transistor, a second thin film transistor, a third thin film transistor, and a light emitting element;
a signal line;
a first power source line;
a second power source line; and
a third power source line,
wherein one of a source and a drain of the first thin film transistor is electrically connected to the signal line and the other of the source and the drain of the first thin film transistor is electrically connected to a gate of the second thin film transistor,
wherein one of a source and a drain of the second thin film transistor is electrically connected to the first power source line and the other of the source and the drain of the second thin film transistor is electrically connected to a first electrode of the light emitting element,
wherein one of a source and a drain of the third thin film transistor is electrically connected to the first electrode of the light emitting element and the other of the source and the drain of the third thin film transistor is directly connected to the third power source line,
wherein a second electrode of the light emitting element is electrically connected to the second power source line, and
wherein a potential of the second power source line is lower than that of the third power source line.
17. A display device comprising:
a pixel including a first thin film transistor, a second thin film transistor, a third thin film transistor, a capacitor, and a light emitting element;
a signal line;
a first power source line;
a second power source line; and
a third power source line,
wherein one of a source and a drain of the first thin film transistor is electrically connected to the signal line and the other of the source and the drain of the first thin film transistor is electrically connected to a gate of the second thin film transistor,
wherein one of a source and a drain of the second thin film transistor is electrically connected to the first power source line and the other of the source and the drain of the second thin film transistor is electrically connected to a first electrode of the light emitting element,
wherein one of a source and a drain of the third thin film transistor is electrically connected to the first electrode of the light emitting element and the other of the source and the drain of the third thin film transistor is directly connected to the third power source line,
wherein a second electrode of the light emitting element is electrically connected to the second power source line,
wherein the capacitor is located between one of the source and the drain of the second thin film transistor and the gate of the second thin film transistor, and
wherein a potential of the second power source line is lower than that of the third power source line.