LIGHT EMITTING DEVICE

• US 20070146254A1
• Filed: 12/18/2006
• Published: 06/28/2007
• Est. Priority Date: 12/27/2005
• Status: Active Grant

• Current Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Original Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Inventors: NAGATSUKA, Shuhei, KIMURA, Akihiro, YANAI, Hiromi
• Granted Patent: US 7,995,012 B2
• Time in Patent Office: Days
• US Class Current: 345/82
• CPC Class Codes: G09G 2300/0842 forming a memory circuit, e.g. a dynamic memory with one capacitor
• CPC Class Codes: G09G 2300/0861 with additional control of the display period without amending the charge stored in a pixel memory, e.g. by means of additional select electrodes
• 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 3/2022 using sub-frames
• CPC Class Codes: G09G 3/3258 with pixel circuitry controlling the voltage across the light-emitting element

Abstract

A display device in which characteristic change of an organic light emitting layer due to deterioration or temperature change can be detected to keep the constant luminance of a light emitting element is provided. A monitor region is provided in addition to a pixel portion for display. A plurality of monitor elements is arranged in the monitor region. A switching circuit is provided so as to prevent a large amount of current from flowing in a shorted monitor element among the plurality of monitor elements. As a result, by monitoring potential change between electrodes of the monitor element, the voltage or the current that is supplied to a light emitting element in the pixel portion for display can be corrected in accordance with time degradation or temperature change.

Claims

1. A light emitting device comprising:

a first monitor element;

a second monitor element;

a monitor line electrically connected to the first monitor element and the second monitor element;

a first circuit for electrically interrupting a current supplied to the first monitor element in a case where anode potential of the first monitor element is lowered; and

a second circuit electronically connected to the second monitor element,

wherein the first circuit is electorically connected to the second circuit.

7. A light emitting device according to claim 1, wherein a buffer amplifier circuit of which input is connected to the monitor line is included, output of the buffer amplifier circuit is connected to one of electrodes of a driving transistor included in a pixel portion, and a voltage applied to a light emitting element included in the pixel portion is changed in according with change of the anode potential of the first monitor element or the second monitor element.

2. A light emitting device comprising:

a first monitor element;

a second monitor element;

a monitor line electrically connected to the first monitor element and the second monitor element;

a first control transistor for controlling supply of a current from the monitor line to the first monitor element;

a second control transistor for controlling supply of a current from the monitor line to the second monitor element;

a first circuit for turning off the first control transistor in a case where anode potential of the first monitor element is lowered; and

a second circuit for turning on the second control transistor in a case where anode potential of the first monitor element is lowered.

8. A light emitting device according to claim 2, wherein a buffer amplifier circuit of which input is connected to the monitor line is included, output of the buffer amplifier circuit is connected to one of electrodes of a driving transistor included in a pixel portion, and a voltage applied to a light emitting element included in the pixel portion is changed in according with change of the anode potential of the first monitor element or the second monitor element.

3. A light emitting device comprising:

a first monitor element;

a second monitor element;

a monitor line electrically connected to the first monitor element and the second monitor element;

a unit for supplying a constant current to the monitor line;

a first control transistor for controlling supply of a current from the monitor line to the first monitor element;

a second control transistor for controlling supply of a current from the monitor line to the second monitor element;

a first circuit for turning off the first control transistor in a case where anode potential of the first monitor element is lowered; and

a second circuit for turning on the second control transistor in a case where anode potential of the first monitor element is lowered.

9. A light emitting device according to claim 3, wherein a buffer amplifier circuit of which input is connected to the monitor line is included, output of the buffer amplifier circuit is connected to one of electrodes of a driving transistor included in a pixel portion, and a voltage applied to a light emitting element included in the pixel portion is changed in according with change of the anode potential of the first monitor element or the second monitor element.

4. A light emitting device comprising:

a first monitor element;

a second monitor element that is paired with the first monitor element;

a monitor line electrically connected to the first monitor element and the second monitor element; and

a circuit for electrically interrupting a current supplied to the first monitor element and turning on the second monitor element in a case where anode potential of the first monitor element is lowered.

10. A light emitting device according to claim 4, wherein a buffer amplifier circuit of which input is connected to the monitor line is included, output of the buffer amplifier circuit is connected to one of electrodes of a driving transistor included in a pixel portion, and a voltage applied to a light emitting element included in the pixel portion is changed in according with change of the anode potential of the first monitor element or the second monitor element.

5. A light emitting device comprising:

a first monitor element;

a second monitor element that is paired with the first monitor element;

a monitor line electrically connected to the first monitor element and the second monitor element;

a first control transistor for controlling supply of a current from the monitor line to the first monitor element;

a second control transistor for controlling supply of a current from the monitor line to the second monitor element; and

a circuit for electrically interrupting the current supplied to the first monitor element and turning on the second monitor element in a case where anode potential of the first monitor element is lowered.

11. A light emitting device according to claim 5, wherein a buffer amplifier circuit of which input is connected to the monitor line is included, output of the buffer amplifier circuit is connected to one of electrodes of a driving transistor included in a pixel portion, and a voltage applied to a light emitting element included in the pixel portion is changed in according with change of the anode potential of the first monitor element or the second monitor element.

6. A light emitting device comprising:

a first monitor element;

a second monitor element that is paired with the first monitor element;

a monitor line electrically connected to the first monitor element and the second monitor element;

a unit for supplying a constant current to the monitor line;

a first control transistor for controlling supply of the current from the monitor line to the first monitor element;

a second control transistor for controlling supply of the current from the monitor line to the second monitor element;

a first circuit for turning off the first control transistor in a case where anode potential of the first monitor element is lowered; and

a second circuit to which potential of one of electrodes of the second monitor element and one of electrodes of the second control transistor is inputted and for outputting a potential to a gate electrode of the second control transistor,

wherein the second circuit has a function for turning on the second monitor element in a case where the anode potential of the first monitor element is lowered.

12. A light emitting device according to claim 6, wherein a buffer amplifier circuit of which input is connected to the monitor line is included, output of the buffer amplifier circuit is connected to one of electrodes of a driving transistor included in a pixel portion, and a voltage applied to a light emitting element included in the pixel portion is changed in according with change of the anode potential of the first monitor element or the second monitor element.