DISPLAY DEVICE

• US 20110140997A1
• Filed: 02/18/2011
• Published: 06/16/2011
• Est. Priority Date: 04/18/2000
• Status: Active Grant

• Current Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Original Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Inventors: Osame, Mitsuaki, Koyama, Jun, Yamazaki, Shunpei, Osada, Mai
• Granted Patent: US 8,194,008 B2
• Time in Patent Office: Days
• US Class Current: 345/76
• CPC Class Codes: G09G 2300/0842 forming a memory circuit, e.g. a dynamic memory with one capacitor
• CPC Class Codes: G09G 2300/0866 by means of changes in the pixel supply voltage
• CPC Class Codes: G09G 2310/0251 Precharge or discharge of pixel before applying new pixel voltage
• CPC Class Codes: G09G 2310/0262 The addressing of the pixel, in a display other than an active matrix LCD, involving the control of two or more scan electrodes or two or more data electrodes, e.g. pixel voltage dependent on signals of two data electrodes
• CPC Class Codes: G09G 2310/027 Details of drivers for data electrodes, the drivers handling digital grey scale data, e.g. use of D/A converters
• CPC Class Codes: G09G 2310/0281 Arrangement of scan or data electrode driver circuits at the periphery of a panel not inherent to a split matrix structure
• CPC Class Codes: G09G 2320/029 by monitoring one or more pixels in the display panel, e.g. by monitoring a fixed reference pixel
• CPC Class Codes: G09G 2320/041 Temperature compensation
• CPC Class Codes: G09G 2320/043 Preventing or counteracting the effects of ageing
• CPC Class Codes: G09G 2330/021 Power management, e.g. power saving
• CPC Class Codes: G09G 2330/028 Generation of voltages supplied to electrode drivers in a matrix display other than LCD
• CPC Class Codes: G09G 3/2022 using sub-frames
• CPC Class Codes: G09G 3/3258 with pixel circuitry controlling the voltage across the light-emitting element
• CPC Class Codes: G09G 3/3266 Details of drivers for scan electrodes
• 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: H10K 59/00 Integrated devices, or assemblies of multiple devices, comprising at least one organic light-emitting element covered by group H10K50/00
• CPC Class Codes: H10K 59/12 Active-matrix OLED [AMOLED] displays

Abstract

The present invention is intended to suppress power consumption of an EL display. In accordance with the brightness of an image to be displayed in a pixel portion, the contrast of the image is determined whether to be inverted or not, and the number of bits of the digital video signal to be input into the pixel portion is reduced, and the magnitude of a current to flow through the EL element is allowed to be maintained at a constant level even when a temperature of an EL layer changes by providing the EL display with another EL element to be used for monitoring a temperature.

Claims

1. A light-emitting device comprising:

a constant current source having an amplifier, a variable resistor and a bipolar transistor, wherein an output of the amplifier is electrically connected to an input of the bipolar transistor, and a first terminal of the bipolar transistor is electrically connected to the variable resistor and an inverted input terminal of the amplifier;

a buffer amplifier;

a first monitoring light emitting element having a pair of electrodes, wherein one of the pair of electrodes is electrically connected to a second terminal of the amplifier and a non-inverted input terminal of the buffer amplifier; and

a second light emitting element having a pair of electrodes, wherein one of the pair of electrodes is electrically connected to an output of the buffer amplifier.

2. A light-emitting device according to claim 1, wherein the buffer amplifier is formed in an IC chip.

3. A light-emitting device according to claim 1, wherein the buffer amplifier is formed on a same substrate as the second light emitting element is formed.

4. A light-emitting device according to claim 1, wherein the constant current source is formed in an IC chip.

5. A light-emitting device according to claim 1, wherein the constant current source is formed on a same substrate as the second light emitting element is formed.

6. A light-emitting device according to claim 1, wherein the first monitoring light emitting element is formed on a same substrate as the second light emitting element is formed.

7. A light-emitting device according to claim 1, wherein the light-emitting device is incorporated in one selected from the group consisting of a telephone, a video camera, a digital camera, a goggle type display, an image reproduction apparatus, and a personal computer.

9. A light-emitting device according to claim 7, wherein the buffer amplifier is formed in an IC chip.

10. A light-emitting device according to claim 7, wherein the buffer amplifier is formed on a same substrate as the second light emitting element is formed.

11. A light-emitting device according to claim 7, wherein the constant current source is formed in an IC chip.

12. A light-emitting device according to claim 7, wherein the constant current source is formed on a same substrate as the second light emitting element is formed.

13. A light-emitting device according to claim 7, wherein the first monitoring light emitting element is formed on a same substrate as the second light emitting element is formed.

14. A light-emitting device according to claim 7, wherein the light-emitting device is incorporated in one selected from the group consisting of a telephone, a video camera, a digital camera, a goggle type display, an image reproduction apparatus, and a personal computer.

8. A light-emitting device comprising:

a constant current source having an amplifier, a variable resistor and a bipolar transistor, wherein an output of the amplifier is electrically connected to an input of the bipolar transistor, and a first terminal of the bipolar transistor is electrically connected to the variable resistor and an inverted input terminal of the amplifier;

a buffer amplifier;

a first monitoring light emitting element having a pair of electrodes, wherein one of the pair of electrodes is electrically connected to a second terminal of the amplifier and a non-inverted input terminal of the buffer amplifier;

a second light emitting element having a pair of electrodes; and

a power source line, wherein the power source line is electrically connected to one of the pair of electrodes of the second light emitting element, and to an output of the buffer amplifier.

15. A light-emitting device comprising:

a constant current source having an amplifier, a variable resistor and a bipolar transistor, wherein an output of the amplifier is electrically connected to an input of the bipolar transistor, and a first terminal of the bipolar transistor is electrically connected to the variable resistor and an inverted input terminal of the amplifier;

a buffer amplifier;

a first monitoring light emitting element having a pair of electrodes, wherein one of the pair of electrodes is electrically connected to a second terminal of the amplifier and a non-inverted input terminal of the buffer amplifier;

a second light emitting element having a pair of electrodes; and

a power source line, wherein an output potential of the buffer amplifier is applied to the power source line, and wherein the power source line is electrically connected to one of the pair of electrodes of the second light emitting element.

16. A light-emitting device according to claim 15, wherein the buffer amplifier is formed in an IC chip.

17. A light-emitting device according to claim 15, wherein the buffer amplifier is formed on a same substrate as the second light emitting element is formed.

18. A light-emitting device according to claim 15, wherein the constant current source is formed in an IC chip.

19. A light-emitting device according to claim 15, wherein the constant current source is formed on a same substrate as the second light emitting element is formed.

20. A light-emitting device according to claim 15, wherein the first monitoring light emitting element is formed on a same substrate as the second light emitting element is formed.

21. A light-emitting device according to claim 15, wherein the light-emitting device is incorporated in one selected from the group consisting of a telephone, a video camera, a digital camera, a goggle type display, an image reproduction apparatus, and a personal computer.