Display device and driving method thereof

• US 7,592,975 B2
• Filed: 08/18/2005
• Issued: 09/22/2009
• Est. Priority Date: 08/27/2004
• Status: Active Grant

• Current Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Original Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Inventors: Osame, Mitsuaki, Koyama, Jun, Yamazaki, Shunpei
• Primary Examiner(s): Mengistu; Amare
• Assistant Examiner(s): SHARIFI-TAFRESHI, KOOSHA
• Application Number:
  US11/208,278
• Publication Number:
  US 20060044229A1
• Time in Patent Office: 1,496 Days
• Field of Search: 257/E27.127, 257/E27.132, 345/60, 345/55, 345/64, 345/67, 345/76, 345/77, 345/82, 345/84, 345 90- 92, 345/214
• US Class Current: 345/60
• CPC Class Codes: G09G 2300/0842 forming a memory circuit, e.g. a dynamic memory with one capacitor
• CPC Class Codes: G09G 2310/0256 with the purpose of reversing the voltage across a light emitting or modulating element within a pixel
• CPC Class Codes: G09G 3/2022 using sub-frames
• CPC Class Codes: G09G 3/3233 with pixel circuitry controlling the current through the light-emitting element
• CPC Class Codes: G09G 3/3291 in which the data driver supplies a variable data voltage for setting the current through, or the voltage across, the light-emitting elements
• CPC Class Codes: G09G 5/399 using two or more bit-mapped memories, the operations of which are switched in time, e.g. ping-pong buffers

Abstract

A display device where a reverse driving voltage can be applied to a light-emitting element at regular intervals in order to insulate a short-circuit portion, thereby prolonging the life of the light-emitting element. A short-circuit portion is burnt out by providing a period for supplying a forward voltage or current to a light-emitting element, and a period for supplying a reverse voltage or current thereto. AC drive is performed only before mounting an AC driver circuit on an electronic appliance, and it is not performed after the mounting. Accordingly, the number of components in an electronic appliance can be reduced as well as the cost reduction of the components can be achieved.

Claims

1. A display device comprising:

a pixel comprising;

a light-emitting element;

a driving transistor;

an AC transistor;

a first path for supplying a forward current to the light-emitting element; and

a second path for supplying a reverse current to the light-emitting element,

wherein the light-emitting element comprises a pixel electrode and an opposing electrode,

wherein one of a source electrode and a drain electrode of the driving transistor is connected to the pixel electrode of the light-emitting element,

wherein one of a source electrode and a drain electrode of the AC transistor is connected to the pixel electrode of the light-emitting element,

wherein the driving transistor is disposed in the first path and the AC transistor is disposed in the second path,

wherein switching between the first path and the second path is controlled by using the driving transistor and the AC transistor, and

wherein the AC transistor is stopped after the display device is mounted on an electronic appliance.

2. The display device according to claim 1,

wherein the driving transistor and the AC transistor have the same conductivity type,

wherein the driving transistor operates in a saturation region, and

wherein the AC transistor operates in a linear region.

3. The display device according to claim 1, wherein the ratio of a channel length of the driving transistor to a channel width thereof is 5 or more to 1.

4. The display device according to claim 1, wherein a channel length of the AC transistor is equal or shorter than a channel width thereof.

5. The display device according to claim 1, wherein the pixel is arranged in matrix.

6. The display device according to claim 1, wherein the electronic appliance is selected from the group consisting of a camera such as a video camera and a digital camera, a goggle type display, a navigation system, an audio reproducing device, a laptop personal computer, a game machine, a mobile computer, a portable phone, a portable game machine, an electronic book, and an image reproducing device provided with a recording medium.

7. A display device comprising:

a pixel comprising;

a light-emitting element;

a driving transistor for controlling the amount of a forward current flowing to the light-emitting element;

a switching transistor for controlling input of a video signal; and

an AC transistor for controlling a reverse current flowing to the light-emitting element,

wherein the light-emitting element comprises a pixel electrode and an opposing electrode,

wherein one of a source electrode and a drain electrode of the driving transistor is connected to the pixel electrode of the light-emitting element,

wherein one of a source electrode and a drain electrode of the AC transistor is connected to the pixel electrode of the light-emitting element, and

wherein the AC transistor is stopped after the display device is mounted on an electronic appliance.

8. The display device according to claim 7,

wherein the driving transistor and the AC transistor have the same conductivity type,

wherein the driving transistor operates in a saturation region, and

wherein the AC transistor operates in a linear region.

9. The display device according to claim 7, wherein the ratio of a channel length of the driving transistor to a channel width thereof is 5 or more to 1.

10. The display device according to claim 7, wherein a channel length of the AC transistor is equal or shorter than a channel width thereof.

11. The display device according to claim 7, wherein the pixel is arranged in matrix.

12. The display device according to claim 7, wherein the electronic appliance is selected from the group consisting of a camera such as a video camera and a digital camera, a goggle type display, a navigation system, an audio reproducing device, a laptop personal computer, a game machine, a mobile computer, a portable phone, a portable game machine, an electronic book, and an image reproducing device provided with a recording medium.

13. A display device comprising:

a pixel comprising;

a light-emitting element;

a driving transistor for controlling the amount of a forward current flowing to the light-emitting element;

a switching transistor for controlling input of a video signal;

an AC transistor for controlling a reverse current flowing to the light-emitting element;

a gate signal line;

a source signal line;

a power source line; and

a current lead-in line,

wherein the light-emitting element comprises a pixel electrode and an opposing electrode,

wherein one of a source electrode and a drain electrode of the driving transistor is connected to the pixel electrode of the light-emitting element,

wherein one of a source electrode and a drain electrode of the AC transistor is connected to the pixel electrode of the light-emitting element,

wherein a gate electrode of the switching transistor is connected to the gate signal line,

wherein the switching transistor is connected to the source signal line and a gate electrode of the driving transistor,

wherein the driving transistor is connected to the power source line and the light-emitting element,

wherein a gate electrode of the AC transistor is connected to the power source line,

wherein the AC transistor is connected to the light-emitting element and the current lead-in line, and

wherein the AC transistor is stopped after the display device is mounted on an electronic appliance.

14. The display device according to claim 13,

wherein the driving transistor and the AC transistor have the same conductivity type,

wherein the driving transistor operates in a saturation region, and

wherein the AC transistor operates in a linear region.

15. The display device according to claim 13, wherein the ratio of a channel length of the driving transistor to a channel width thereof is 5 or more to 1.

16. The display device according to claim 13, wherein a channel length of the AC transistor is equal or shorter than a channel width thereof.

17. The display device according to claim 13, wherein the pixel is arranged in matrix.

18. The display device according to claim 13, wherein a potential of the power source line is fixed, and a potential of a counter electrode of the light-emitting element is changed according to the direction of a current flowing to the light-emitting element.

19. The display device according to claim 13, wherein the electronic appliance is selected from the group consisting of a camera such as a video camera and a digital camera, a goggle type display, a navigation system, an audio reproducing device, a laptop personal computer, a game machine, a mobile computer, a portable phone, a portable game machine, an electronic book, and an image reproducing device provided with a recording medium.

20. A display device comprising:

a pixel comprising;

a light-emitting element;

a driving transistor for controlling the amount of a forward current flowing to the light-emitting element;

an AC transistor;

a switching transistor for controlling input of a video signal; and

an AC driver circuit for applying an AC signal to the light-emitting element,

wherein the light-emitting element comprises a pixel electrode and an opposing electrode,

wherein one of a source electrode and a drain electrode of the driving transistor is connected to the pixel electrode of the light-emitting element,

wherein one of a source electrode and a drain electrode of the AC transistor is connected to the pixel electrode of the light-emitting element,

wherein the driving transistor operates in the linear region, and

wherein the AC driver circuit is stopped after the display device is mounted on an electronic appliance.

21. The display device according to claim 20, wherein the pixel is arranged in matrix.

22. The display device according to claim 20, wherein the electronic appliance is selected from the group consisting of a camera such as a video camera and a digital camera, a goggle type display, a navigation system, an audio reproducing device, a laptop personal computer, a game machine, a mobile computer, a portable phone, a portable game machine, an electronic book, and an image reproducing device provided with a recording medium.