Display device and driving method thereof
To provide a display device and a driving method thereof, where variations in the threshold voltage of transistors can be compensated and thus variations in luminance of light-emitting elements can be suppressed. In a first period, initialization is performed; in a second period, a voltage based on the threshold voltage of a first transistor is held in first and second storage capacitors; in a third period, a voltage based on a video signal voltage and the threshold voltage of the first transistor is held in the first and second storage capacitors; and in a fourth period, voltages held in the first and second storage capacitors are applied to a gate terminal of the first transistor to supply a current to a light-emitting element, so that the light-emitting element emits light. Through the operation process, a current obtained by compensating variations in the threshold voltage of the first transistor can be supplied to the light-emitting element, thereby variations in luminance can be suppressed.
1. A semiconductor device comprising:
a transistor;
a capacitor;
a first switch;
a second switch;
a third switch; and
a fourth switch;
wherein a conductive layer comprises a region serving as a gate of the transistor and a region serving as a first electrode of the capacitor,
wherein one of a source and a drain of the transistor is electrically connected to a third wiring,
wherein a first terminal of the first switch is electrically connected to the gate of the transistor through a second conductive layer,
wherein a second terminal of the first switch is electrically connected to the other of the source and the drain of the transistor,
wherein a first terminal of the second switch is electrically connected to the other of the source and the drain of the transistor,
wherein a second terminal of the second switch is electrically connected to a pixel electrode,
wherein a first terminal of the third switch is electrically connected to a first wiring,
wherein a second terminal of the third switch is electrically connected to a semiconductor layer comprising a region serving as a second electrode of the capacitor,
wherein a first terminal of the fourth switch is electrically connected to a second wiring, and
wherein a second terminal of the fourth switch is electrically connected to the second electrode.
2. The semiconductor device according to claim 1 , wherein the second terminal of the third switch is electrically connected to the semiconductor layer through a third conductive layer.
3. The semiconductor device according to claim 2 , wherein the transistor comprises a channel formation region comprising polysilicon.
4. The semiconductor device according to claim 2 ,
wherein the first switch, the second switch, the third switch, and the fourth switch are a second transistor, a third transistor, a fourth transistor, and a fifth transistor, respectively, and
wherein a ratio of a channel width to a channel length in the transistor is larger than a ratio of a channel width to a channel length in the second transistor, a ratio of a channel width to a channel length in the third transistor, a ratio of a channel width to a channel length in the fourth transistor, and a ratio of a channel width to a channel length in the fifth transistor.
5. The semiconductor device according to claim 1 , wherein a light-emitting element comprises the pixel electrode.
6. The semiconductor device according to claim 5 , wherein the second terminal of the third switch is electrically connected to the semiconductor layer through a third conductive layer.
7. The semiconductor device according to claim 1 , wherein the transistor comprises a channel formation region comprising polysilicon.
8. The semiconductor device according to claim 1 ,
wherein the first switch, the second switch, the third switch, and the fourth switch are a second transistor, a third transistor, a fourth transistor, and a fifth transistor, respectively, and
wherein a ratio of a channel width to a channel length in the transistor is larger than a ratio of a channel width to a channel length in the second transistor, a ratio of a channel width to a channel length in the third transistor, a ratio of a channel width to a channel length in the fourth transistor, and a ratio of a channel width to a channel length in the fifth transistor.
9. A semiconductor device comprising:
a transistor;
a light-emitting element;
a first capacitor whose first electrode is electrically connected to a gate of the transistor;
a second capacitor whose first electrode is electrically connected to the gate of the transistor;
a first switch capable of controlling conduction and non-conduction between the gate of the transistor and one of a source and a drain of the transistor
a second switch capable of controlling conduction and non-conduction between the one of a source and a drain of the transistor and a first electrode of the light-emitting element;
a first wiring capable of transmitting a video signal;
a third switch capable of controlling conduction and non-conduction between the first wiring and a second electrode of the first capacitor;
a second wiring capable of transmitting a potential lower than a potential of the other of the source and the drain of the transistor;
a fourth switch capable of controlling conduction and non-conduction between the second wiring and the second electrode of the first capacitor; and
a fifth switch capable of controlling conduction and non-conduction between the second electrode of the first capacitor and the one of the source and the drain of the transistor;
wherein a second electrode of the second capacitor is electrically connected to the second wiring, and
wherein a potential of the other of the source and the drain of the transistor is higher than a potential of a second electrode of the light-emitting element.
10. An electronic device comprising the semiconductor device according to claim 9 .
11. The semiconductor device according to claim 9 , wherein the transistor comprises a channel formation region comprising polysilicon.
12. The semiconductor device according to claim 9 ,
wherein the first switch, the second switch, the third switch, the fourth switch, and the fifth switch are a second transistor, a third transistor, a fourth transistor, and a fifth transistor, and a sixth transistor, respectively, and
wherein a ratio of a channel width to a channel length in the transistor is larger than a ratio of a channel width to a channel length in the second transistor, a ratio of a channel width to a channel length in the third transistor, a ratio of a channel width to a channel length in the fourth transistor, a ratio of a channel width to a channel length in the fifth transistor, and a ratio of a channel width to a channel length in the sixth transistor.