Display device and method for driving the same

• US 20070242031A1
• Filed: 04/03/2007
• Published: 10/18/2007
• Est. Priority Date: 04/14/2006
• Status: Active Grant

• Current Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Original Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Inventors: Umezaki, Atsushi, Kimura, Hajime, Yamazaki, Shunpei, Yoshida, Yasunori, Yanagisawa, Makoto, Shishido, Hideaki
• Granted Patent: US 8,159,449 B2
• Time in Patent Office: Days
• US Class Current: 345/102
• CPC Class Codes: G02F 1/133603 with LEDs
• CPC Class Codes: G02F 1/1362 Active matrix addressed cells G02F1/134336, G02F1/134363 take precedence
• CPC Class Codes: G09G 2300/046 with an emissive area and a light-modulating area combined in one pixel
• CPC Class Codes: G09G 2320/0238 Improving the black level
• CPC Class Codes: G09G 2320/062 Adjustment of illumination source parameters
• CPC Class Codes: G09G 2320/066 for control of contrast
• CPC Class Codes: G09G 2330/021 Power management, e.g. power saving
• CPC Class Codes: G09G 3/3208 organic, e.g. using organic light-emitting diodes [OLED]
• CPC Class Codes: G09G 3/3426 the different display panel areas being distributed in two dimensions, e.g. matrix
• CPC Class Codes: G09G 3/36 using liquid crystals
• CPC Class Codes: G09G 3/3648 using an active matrix G09G3/367 - G09G3/3696 take precedence

Abstract

It is an object to provide a display device in which a problem of light leakage from a liquid crystal element in black display is reduced or overcome and the contrast is improved. It is another object to provide a pixel circuit having a function to control a lighting state of a backlight based on each pixel. These objects are achieved by turning off a light-emitting element in display of a black gray scale, and by providing a light-emitting element in each pixel and providing, in a pixel circuit, a function to individually control lighting and non-lighting of the light-emitting element depending on a gray scale to perform display. When a backlight is provided in each pixel, a light-emitting element that is a backlight is turned off when a black gray scale is displayed, whereby reduction in contrast due to light leakage from a liquid crystal element can be prevented.

Claims

1. A display device comprising:

a pixel portion including a light-emitting element and a liquid crystal element which is overlapped with the light-emitting element;

a data line electrically connected to the liquid crystal element; and

a comparator electrically connected to the data line and the light-emitting element.

2. The display device according to claim 1, wherein light-emission of the light-emitting element passes through the liquid crystal element.

3. The display device according to claim 1, wherein light is transmitted through the liquid crystal element in a state where a voltage is applied or in a state where a voltage is not applied.

4. An electronic device comprising the display device according to claim 1 in a display portion.

5. The display device according to claim 1, wherein a potential based on an analog signal is applied to the data line.

6. A display device comprising:

a pixel portion including a light-emitting element and a liquid crystal element which is overlapped with the light-emitting element;

a data line electrically connected to the liquid crystal element;

a first comparator electrically connected to the data line and the light-emitting element;

a second comparator electrically connected to the data line and the light-emitting element;

a first switch electrically connected to the data line and the first comparator; and

a second switch electrically connected to the data line and the second comparator.

7. The display device according to claim 6, wherein light-emission of the light-emitting element passes through the liquid crystal element.

8. The display device according to claim 6, wherein light is transmitted through the liquid crystal element in a state where a voltage is applied or in a state where a voltage is not applied.

9. An electronic device comprising the display device according to claim 6 in a display portion.

10. The display device according to claim 6, wherein a potential based on an analog signal is applied to the data line.

11. A method for driving a display device, which comprises a pixel portion including a light-emitting element and a liquid crystal element which is overlapped with the light-emitting element;

a data line electrically connected to the liquid crystal element; and

a comparator electrically connected to the data line and the light-emitting element, comprising the steps of;

supplying a potential based on an analog signal to the data line for driving the liquid crystal element;

comparing a potential of the data line with a reference potential in the comparator; and

controlling light-emission of the light-emitting element based on a comparison result by the comparator.

12. The method for driving a display device according to claim 11, wherein light-emission of the light-emitting element passes through the liquid crystal element.

13. The method for driving a display device according to claim 11, wherein light is transmitted through the liquid crystal element in a state where a voltage is applied or in a state where a voltage is not applied.

14. A method for driving a display device, which comprises a pixel portion including a light-emitting element and a liquid crystal element which is overlapped with the light-emitting element;

a data line electrically connected to the liquid crystal element;

a first comparator and a second comparator each electrically connected to the data line and the light-emitting element;

a first switch electrically connected to the data line and the first comparator; and

a second switch electrically connected to the data line and the second comparator, comprising the steps of;

supplying a potential based on an analog signal to the data line for driving the liquid crystal element;

comparing a potential of the data line with a first reference potential in the first comparator by turning on the first switch when the potential of the data line has a negative value;

comparing a potential of the data line with a second reference potential in the second comparator by turning on the second switch when the potential of the data line has a positive value; and

controlling light-emission of the light-emitting element based on a comparison result by the first comparator or a comparison result by the second comparator.

15. The method for driving a display device according to claim 14, wherein light-emission of the light-emitting element passes through the liquid crystal element.

16. The method for driving a display device according to claim 14, wherein light is transmitted through the liquid crystal element in a state where a voltage is applied or in a state where a voltage is not applied.