Light emitting device

• US 7,995,012 B2
• Filed: 12/18/2006
• Issued: 08/09/2011
• 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, Yanai, Hiromi, Kimura, Akihiro
• Primary Examiner(s): Eisen; Alexander
• Assistant Examiner(s): MISHLER, ROBIN J
• Application Number:
  US11/612,226
• Publication Number:
  US 20070146254A1
• Time in Patent Office: 1,695 Days
• Field of Search: 345 76- 83, 315/169.3, 372 3801- 3809, 372/38.1
• 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 depending on data received by the first circuit from the first monitor element in a case where anode potential of the first monitor element is lowered;

a second circuit electrically connected to the second monitor element;

a first inverter provided in the first circuit and having an input terminal connected to an anode electrode of the first monitor element; and

a second inverter provided in the second circuit and having an input terminal connected to an anode electrode of the second monitor element,

wherein the first circuit is electrically connected to the second circuit, and

wherein a negative power supply of the second inverter is connected to the input terminal of the first inverter.

5. A light emitting device according to claim 1, further comprising a buffer amplifier circuit that includes an input connected to the monitor line and an output connected to one of electrodes of a driving transistor included in a pixel portion,

wherein a voltage applied to a light emitting element included in the pixel portion is changed in accordance with a change of the anode potential of the first monitor element or in accordance with a change of an anode potential of 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 depending on data received by the first circuit from the first monitor element in a case where anode potential of the first monitor element is lowered;

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

a first inverter provided in the first circuit and having an input terminal connected to an anode electrode of the first monitor element; and

a second inverter provided in the second circuit and having an input terminal connected to an anode electrode of the second monitor element,

wherein a negative power supply of the second inverter is connected to the input terminal of the first inverter.

6. A light emitting device according to claim 2, further comprising a buffer amplifier circuit that includes an input connected to the monitor line and an output connected to one of electrodes of a driving transistor included in a pixel portion,

wherein a voltage applied to a light emitting element included in the pixel portion is changed in accordance with a change of the anode potential of the first monitor element or in accordance with a change of an anode potential of 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 depending on data received by the first circuit from the first monitor element in a case where anode potential of the first monitor element is lowered;

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

a first inverter provided in the first circuit and having an input terminal connected to an anode electrode of the first monitor element; and

a second inverter provided in the second circuit and having an input terminal connected to an anode electrode of the second monitor element,

wherein a negative power supply of the second inverter is connected to the input terminal of the first inverter.

7. A light emitting device according to claim 3, further comprising a buffer amplifier circuit that includes an input connected to the monitor line and an output connected to one of electrodes of a driving transistor included in a pixel portion,

wherein a voltage applied to a light emitting element included in the pixel portion is changed in accordance with a change of the anode potential of the first monitor element or in accordance with a change of an anode potential of 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;

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 depending on data received by the first circuit from the first monitor element in a case where anode potential of the first monitor element is lowered;

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;

a first inverter provided in the first circuit and having an input terminal connected to an anode electrode of the first monitor element; and

a second inverter provided in the second circuit and having an input terminal connected to an anode electrode of the second monitor element,

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, and

wherein a negative power supply of the second inverter is connected to the input terminal of the first inverter.

8. A light emitting device according to claim 4, further comprising a buffer amplifier circuit that includes an input connected to the monitor line and an output connected to one of electrodes of a driving transistor included in a pixel portion,

wherein a voltage applied to a light emitting element included in the pixel portion is changed in accordance with a change of the anode potential of the first monitor element or in accordance with a change of an anode potential of the second monitor element.