Organic EL display device

• US 6,812,650 B2
• Filed: 04/02/2003
• Issued: 11/02/2004
• Est. Priority Date: 04/03/2002
• Status: Expired due to Term

• Current Assignee: Sanyo Electric Company Limited (Panasonic Holdings Corporation)
• Original Assignee: Sanyo Electric Company Limited (Panasonic Holdings Corporation)
• Inventors: Chiba, Hidenori, Yasuda, Hitoshi
• Primary Examiner(s): VU, DAVID HUNG
• Application Number:
  US10/405,038
• Publication Number:
  US 20040012340A1
• Time in Patent Office: 580 Days
• Field of Search: 315/169.3, 315/169.1, 345/76, 345/77
• US Class Current: 315/169.1
• CPC Class Codes: G09G 2300/043 Compensation electrodes or other additional electrodes in matrix displays related to distortions or compensation signals, e.g. for modifying TFT threshold voltage in column driver
• 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 2320/0276 for the purpose of adaptation to the characteristics of a display device, i.e. gamma correction
• CPC Class Codes: G09G 2320/043 Preventing or counteracting the effects of ageing
• CPC Class Codes: G09G 2320/0626 for control of overall brightness
• CPC Class Codes: G09G 2320/0673 for control of gamma adjustment, e.g. selecting another gamma curve
• CPC Class Codes: G09G 2330/02 Details of power systems and of start or stop of display operation
• CPC Class Codes: G09G 2330/028 Generation of voltages supplied to electrode drivers in a matrix display other than LCD
• CPC Class Codes: G09G 2360/144 the light being ambient light
• CPC Class Codes: G09G 2360/145 the light originating from the display screen
• CPC Class Codes: G09G 3/3233 with pixel circuitry controlling the current through the light-emitting element
• CPC Class Codes: G09G 5/02 characterised by the way in which colour is displayed details of colour display specific for CRTs G09G1/28; specific for flat matrix panels other than liquid crystal displays G09G3/2003; specific for liquid crystal displays G09G3/3607

Abstract

An organic electroluminescent display device includes a plurality of electroluminescent elements and a plurality of thin film transistors. Each of the electroluminescent elements includes an anode, a cathode and a light emitting layer disposed between the anode and the cathode. Each of the thin film transistors drives one of the electroluminescent elements. A first power supply is connected to the thin film transistors and supplies a power supply voltage to the thin film transistors. The first power supply changes the power supply voltage so that luminance of the light emitting layers vary. A second power supply is connected to the electroluminescent elements and supplies a reference voltage to the electroluminescent elements. Because the power supply voltage itself varies, it is easy to adjust the brightness of the display device.

Claims

1. An organic electroluminescent display device comprising:

a plurality of electroluminescent elements, each of the electroluminescent elements comprising an anode, a cathode and a light emitting layer disposed between the anode and the cathode;

a plurality of thin film transistors, each of the thin film transistors driving a corresponding one of the electroluminescent elements;

a first power supply connected to the thin film transistors and supplying a power supply voltage to the thin film transistors, the first power supply changing the power supply voltage so that luminance of the light emitting layers vary; and

a second power supply connected to the electroluminescent elements and supplying a reference voltage to the electroluminescent elements.

2. The organic electroluminescent display device of claim 1, wherein the first power supply comprises a DC—

DC converter, and the DC—

DC converter changes the power supply voltage in response to a feedback voltage.

4. The organic electroluminescent display device of claim 2, wherein each of the first, second and third power supplies comprises a DC—

DC converter, and the DC—

DC converter changes the corresponding power supply voltage in response to a feedback voltage.

3. An organic electroluminescent display device comprising:

a plurality of electroluminescent elements for red light emission, each of the electroluminescent elements for red light emission comprising an anode, a cathode and a red light emitting layer disposed between the anode and the cathode of the electroluminescent element for red light emission;

a plurality of electroluminescent elements for green light emission, each of the electroluminescent elements for green light emission comprising an anode, a cathode and a green light emitting layer disposed between the anode and the cathode of the electroluminescent element for green light emission;

a plurality of electroluminescent elements for blue light emission, each of the electroluminescent elements for blue light emission comprising an anode, a cathode and a blue light emitting layer disposed between the anode and the cathode of the electroluminescent element for blue light emission;

a plurality of thin film transistors, each of the thin film transistors driving a corresponding one of the electroluminescent elements;

a first power supply connected to the thin film transistors driving the electroluminescent elements for red light emission for supplying a first power supply voltage, the first power supply changing the first power supply voltage so that luminance of the red light emitting layers vary;

a second power supply connected to the thin film transistors driving the electroluminescent elements for green light emission for supplying a second power supply voltage, the second power supply changing the second power supply voltage so that luminance of the green light emitting layers vary;

a third power supply connected to the thin film transistors driving the electroluminescent elements for blue light emission for supplying a third power supply voltage, the third power supply changing the third power supply voltage so that luminance of the blue light emitting layers vary; and

a reference voltage supply connected to the electroluminescent elements for red light emission, the electroluminescent elements for green light emission and the electroluminescent elements for blue light emission for supplying a reference voltage.

5. An organic electroluminescent display device comprising:

a plurality of electroluminescent elements, each of the electroluminescent elements comprising an anode, a cathode and a light emitting layer disposed between the anode and the cathode;

a plurality of thin film transistors, each of the thin film transistors driving a corresponding one of the electroluminescent elements;

a sensor;

a first power supply connected to the thin film transistors and supplying a power supply voltage to the thin film transistors, the first power supply changing the power supply voltage in response to an output of the sensor; and

a second power supply connected to the electroluminescent elements and supplying a reference voltage to the electroluminescent elements.

6. The organic electroluminescent display device of claim 5, wherein the sensor comprises a photo sensor that detects brightness and changes the output based on the detected brightness.

7. The organic electroluminescent display device of claim 5, wherein the first power supply comprises a DC—

DC converter, and the DC—

DC converter changes the power supply voltage in response to a feedback voltage.

8. An organic electroluminescent display device comprising:

a plurality of electroluminescent elements for red light emission, each of the electroluminescent elements for red light emission comprising an anode, a cathode and a red light emitting layer disposed between the anode and the cathode of the electroluminescent element for red light emission;

a plurality of electroluminescent elements for green light emission, each of the electroluminescent elements for green light emission comprising an anode, a cathode and a green light emitting layer disposed between the anode and the cathode of the electroluminescent element for green light emission;

a plurality of electroluminescent elements for blue light emission, each of the electroluminescent elements for blue light emission comprising an anode, a cathode and a blue light emitting layer disposed between the anode and the cathode of the electroluminescent element for blue light emission;

a plurality of thin film transistors, each of the thin film transistors driving a corresponding one of the electroluminescent elements;

a sensor;

a first power supply connected to the thin film transistors driving the electroluminescent elements for red light emission for supplying a first power supply voltage, the first power supply changing the first power supply voltage in response to an output of the sensor;

a second power supply connected to the thin film transistors driving the electroluminescent elements for green light emission for supplying a second power supply voltage, the second power supply changing the second power supply voltage in response to the output of the sensor;

a third power supply connected to the thin film transistors driving the electroluminescent elements for blue light emission for supplying a third power supply voltage, the third power supply changing the third power supply voltage in response to the output of the sensor; and

a reference voltage supply connected to the electroluminescent elements for red light emission, the electroluminescent elements for green light emission and the electroluminescent elements for blue light emission for supplying a reference voltage.

9. The organic electroluminescent display device of claim 8, wherein the sensor comprises a photo sensor that detects brightness and changes the output based on the detected brightness.

10. The organic electroluminescent display device of claim 8, wherein each of the first, second and third power supplies comprises a DC—

DC converter, and the DC—

DC converter changes the corresponding power supply voltage in response to a feedback voltage.