Organic electroluminescent display device

• US 20060012311A1
• Filed: 07/12/2005
• Published: 01/19/2006
• Est. Priority Date: 07/12/2004
• Status: Abandoned Application

• Current Assignee: Sanyo Electric Company Limited (Panasonic Holdings Corporation)
• Original Assignee: Sanyo Electric Company Limited (Panasonic Holdings Corporation)
• Inventors: Ogawa, Takashi
• Application Number:
  US11/178,601
• Publication Number:
  US 20060012311A1
• Time in Patent Office: Days
• US Class Current: 315/169.300
• CPC Class Codes: G09G 2300/0842 forming a memory circuit, e.g. a dynamic memory with one capacitor
• CPC Class Codes: G09G 2300/0852 being a dynamic memory with more than one capacitor
• 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 2320/0295 by monitoring each display pixel
• CPC Class Codes: G09G 2320/043 Preventing or counteracting the effects of ageing
• CPC Class Codes: G09G 2320/045 Compensation of drifts in the characteristics of light emitting or modulating elements
• CPC Class Codes: G09G 2320/0666 for control of colour parameters, e.g. colour temperature
• CPC Class Codes: G09G 2330/021 Power management, e.g. power saving
• CPC Class Codes: G09G 2360/145 the light originating from the display screen
• CPC Class Codes: G09G 2360/148 the light being detected by light detection means within each pixel
• CPC Class Codes: G09G 3/3233 with pixel circuitry controlling the current through the light-emitting element
• 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 59/13 comprising photosensors that control luminance

Abstract

A photosensor is disposed in each pixel, and the brightness is adjusted for each pixel depending on the light quantity of an organic EL element. The adjustment of brightness is realized by making the current amount of a pixel with a high brightness small in accordance with a pixel with a small light emission amount. Thus, low power consumption can be achieved, and the unevenness of brightness can be corrected. By disposing the photosensor to configure a photoreceptor circuit in each pixel, the unevenness of brightness is corrected. Further, it becomes possible to correct brightness in a brightness half-life. Hence, a longer lifetime can be achieved.

Claims

1. An organic electroluminescent display device comprising:

a plurality of drain lines and a plurality of gate lines disposed in a matrix form on a substrate;

a plurality of light emitting pixels disposed on the substrate in accordance with the matrix form of the drain lines and the gate lines, each of the light emitting pixels comprising a drive transistor, a selection transistor and an organic electroluminescent element; and

a plurality of photosensors disposed on the substrate and each provided for corresponding light emitting pixels to measure brightness of corresponding organic electroluminescent elements.

2. The display device of claim 1, wherein each of the photosensors covers part of a corresponding organic electroluminescent element.

3. An organic electroluminescent display device comprising:

a plurality of drain lines and a plurality of gate lines disposed in a matrix form on a substrate;

a plurality of light emitting pixels disposed on the substrate in accordance with the matrix form of the drain lines and the gate lines, each of the light emitting pixels comprising a drive transistor, a selection transistor and an organic electroluminescent element; and

a photosensor disposed in each of the light emitting pixels and comprising a photosensor transistor, a gate of the photosensor transistor receiving a constant voltage, a source or a drain of the photosensor transistor being connected with a power supply terminal of the drive transistor, and the source or the drain of the photosensor transistor that is not connected with the power supply terminal being connected with a control terminal of the drive transistor.

4. The display device of claim 3, wherein the photosensor covers part of a corresponding organic electroluminescent element.

5. The display device of claim 3, wherein the organic electroluminescent element is configured to receive less current when the photosensor receives more light from the organic electroluminescent element.

6. The display device of claim 3, wherein the photosensor transistor is a thin film transistor comprising the gate, an insulation film and a semiconductor layer stacked on the substrate, the thin film transistor further comprising a channel provided in the semiconductor layer, the source formed at one end of the channel and the drain formed at another end of the channel and converting light incident thereon into an electric signal.

7. The display device of claim 6, wherein the semiconductor layer is configured to receive the light in a junction region between the source and the channel of the or between the drain and the channel.

8. The display device of claim 6, wherein a low concentration impurity region is provided between the source and the channel or between the drain and the channel.

9. The display device of claim 8, wherein the low concentration impurity region is provided on a side of the semiconductor layer outputting a photocurrent generated by incident light.

10. An organic electroluminescent display device comprising:

a plurality of drain lines and a plurality of gate lines disposed in a matrix form on a substrate;

a plurality of light emitting pixels disposed on the substrate in accordance with the matrix form of the drain lines and the gate lines, each of the light emitting pixels comprising a drive transistor, a selection transistor and an organic electroluminescent element; and

a photosensor disposed in each of the light emitting pixels and measuring brightness of a corresponding organic electroluminescent element, the photosensor being configured to change a photosensitivity thereof.

11. The display device of claim 10, wherein the photosensor covers part of a corresponding organic electroluminescent element.

12. The display device of claim 10, wherein a reference voltage of data signals supplied to the drain lines is selected based on the measured brightness.

13. The display device of claim 10, wherein the photosensor comprises;

a thin film transistor converting light incident thereon into an electric signal,

a first power supply line supplying a high potential and a second power supply line supplying a low potential,

a first switching transistor connected with the thin film transistor in series between the first power supply line and the second power supply line,

a second switching transistor connected with a resistor in series between the first power supply line and the second power supply line, and

a capacitor, a first capacitor terminal of the capacitor being connected with a control terminal of the second switching transistor and a second capacitor terminal of the capacitor being connected with the first power supply line or the second power supply line.

14. The display device of claim 13, wherein the first power supply line is connected to the drive transistor.

15. The display device of claim 13, wherein the thin film transistor comprises a gate, an insulation film and a semiconductor layer stacked on the substrate and further comprises a channel provided in the semiconductor layer, a source formed at one end of the channel and a drain formed at another end of the channel, and the semiconductor layer is configured to receive the light in a junction region between the source and the channel or between the drain and the channel.

16. The display device of claim 13, wherein the thin film transistor comprises a gate, an insulation film and a semiconductor layer stacked on the substrate and further comprises a channel provided in the semiconductor layer, a source formed at one end of the channel and a drain formed at another end of the channel, and a low concentration impurity region is provided between the source and the channel or between the drain and the channel.

17. The display device of claim 16, wherein the low concentration impurity region is provided on a side of the semiconductor layer outputting a photocurrent generated by incident light.