PIXEL CIRCUIT AND DISPLAY DEVICE

• US 20130021228A1
• Filed: 11/30/2010
• Published: 01/24/2013
• Est. Priority Date: 12/02/2009
• Status: Abandoned Application

• Current Assignee: Global OLED Technology LLC (LG Display Co., Ltd.)
• Original Assignee: Global OLED Technology LLC (LG Display Co., Ltd.)
• Inventors: Miwa, Koichi, Maekawa, Yuichi
• Application Number:
  US13/513,157
• Publication Number:
  US 20130021228A1
• Time in Patent Office: Days
• US Class Current: 345/76
• CPC Class Codes: G09G 2300/0819 used for counteracting undesired variations, e.g. feedback or autozeroing
• 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 2320/043 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 2330/021 Power management, e.g. power saving
• CPC Class Codes: G09G 3/3233 with pixel circuitry controlling the current through the light-emitting element

Abstract

[Problem to be solved] To achieve low power consumption. [Solution] The driving transistor T1 supplies driving current from the power supply VDD to the organic EL elements OLED. The source end of the driving transistor T1 connected to one end of the said organic EL elements OLED, the other end of the organic EL elements OLED is connected to the power supply potential Vss, and the mutual conductance per display unit area of the said organic EL elements of the said driving transistor is equal to or higher than 1×10⁻¹¹ (A/V²/m²).

Claims

1. A pixel circuit comprising:

organic EL elements; and

a driving transistor for supplying current from a power supply to the said organic EL elements, wherein;

a source end of the said driving transistor is connected to one end of the said organic EL elements, the other end of the said organic EL elements is connected to a power supply potential,

characterized in that mutual conductance per display unit area of the said organic EL elements of the said driving transistor is equal to or higher than 1×

10<sup>−

11</sup> (A/V²/m²).

2. The pixel circuit according to claim 1, characterized in that the mutual conductance of the said driving transistor is made higher by satisfying one of the followings:

a channel capacitance is made larger when the mobility of the driving transistor is equal to or greater than 15 cm² Vs with the gate voltage equal to or less than 20V;

or

the thickness of a gate insulator of the driving transistor is equal to or less than 1000 angstrom;

or the light from the said organic EL elements transmit to the driving transistor with a maximum wavelength transmittance of 70% or higher against the channel layer of the driving transistor or against visible light of the source electrode and also the driving transistor is made larger.

3. The pixel circuit according to claim 2, characterized in that

the driving transistor is a thin-film transistor (TFT) and

the channel layer of the driving TFT is formed with polysilicon or amorphous silicon or microcrystalline silicon or oxide semiconductor.

4. The pixel circuit according to claim 1 characterized in that the threshold voltage of the driving TFT or turn on voltage of the organic EL elements or their sum is added to the gradation signal voltage and applied to the gate of the driving TFT.

5. The pixel circuit according to claim 1 characterized in that the temperature of the organic elements is presumed from ambient temperature, temperature of the display, display image or history of display image, and a function to adjust power supply voltage which is supplied to pixels or signal voltage is included.

6. A display device characterized in that it comprises the pixel circuit according to claim 1.

7. The pixel circuit according to claim 2 characterized in that the threshold voltage of the driving TFT or turn on voltage of the organic EL elements or their sum is added to the gradation signal voltage and applied to the gate of the driving TFT.

8. The pixel circuit according to claim 3 characterized in that the threshold voltage of the driving TFT or turn on voltage of the organic EL elements or their sum is added to the gradation signal voltage and applied to the gate of the driving TFT.

9. The pixel circuit according to claim 2 characterized in that the temperature of the organic elements is presumed from ambient temperature, temperature of the display, display image or history of display image, and a function to adjust power supply voltage which is supplied to pixels or signal voltage is included.

10. The pixel circuit according to claim 3 characterized in that the temperature of the organic elements is presumed from ambient temperature, temperature of the display, display image or history of display image, and a function to adjust power supply voltage which is supplied to pixels or signal voltage is included.

11. The pixel circuit according to claim 4 characterized in that the temperature of the organic elements is presumed from ambient temperature, temperature of the display, display image or history of display image, and a function to adjust power supply voltage which is supplied to pixels or signal voltage is included.

12. The pixel circuit according to claim 7 characterized in that the temperature of the organic elements is presumed from ambient temperature, temperature of the display, display image or history of display image, and a function to adjust power supply voltage which is supplied to pixels or signal voltage is included.

13. The pixel circuit according to claim 8 characterized in that the temperature of the organic elements is presumed from ambient temperature, temperature of the display, display image or history of display image, and a function to adjust power supply voltage which is supplied to pixels or signal voltage is included.

14. A display device characterized in that it comprises the pixel circuit according to claim 2.

15. A display device characterized in that it comprises the pixel circuit according to claim 3.

16. A display device characterized in that it comprises the pixel circuit according to claim 4.

17. A display device characterized in that it comprises the pixel circuit according to claim 7.

18. A display device characterized in that it comprises the pixel circuit according to claim 8.

19. A display device characterized in that it comprises the pixel circuit according to claim 5.

20. A display device characterized in that it comprises the pixel circuit according to claim 9.