Display device and driving method thereof

• US 20060103324A1
• Filed: 11/14/2005
• Published: 05/18/2006
• Est. Priority Date: 11/15/2004
• Status: Active Grant

• Current Assignee: Samsung Electronics Co. Ltd., Seoul National University Industry Foundation (Seoul National University)
• Original Assignee: Samsung Electronics Co. Ltd., Seoul National University Industry Foundation (Seoul National University)
• Inventors: Lee, Jae-Hoon, Han, Min-Koo, Kim, Ji-Hoon
• Granted Patent: US 8,619,006 B2
• Time in Patent Office: Days
• US Class Current: 315/169.300
• 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 2310/0251 Precharge or discharge of pixel before applying new pixel voltage
• CPC Class Codes: G09G 2310/0254 Control of polarity reversal in general, other than for liquid crystal displays
• CPC Class Codes: G09G 2320/043 Preventing or counteracting the effects of ageing
• 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

A display device has a plurality of pixels, where each pixel includes a light emitting element, a capacitor, a driving transistor having a control terminal, an input terminal, and an output terminal and supplying a driving current to the light emitting element to emit light, a first switching unit diode-connecting the driving transistor and supplying a data voltage to the capacitor in response to a scanning signal, and a second switching unit supplying a driving voltage to the driving transistor and connecting the capacitor to the driving transistor in response to the emission signal, wherein the capacitor is connected to the driving transistor through the first switching unit, stores a control voltage depending on the data voltage and the threshold voltage of the driving transistor, and is connected to the driving transistor through the second switching unit to supply the control voltage to the driving transistor.

Claims

1. A display device comprising a plurality of pixels, each pixel including:

a light emitting element;

a capacitor;

a driving transistor having a control terminal, an input terminal, and an output terminal and supplying a driving current to the light emitting element to emit light;

a first switching unit diode-connecting the driving transistor and supplying a data voltage to the capacitor in response to a scanning signal; and

a second switching unit supplying a driving voltage to the driving transistor and connecting the capacitor to the driving transistor in response to an emission signal,

wherein the capacitor is connected to the driving transistor through the first switching unit, stores a control voltage depending on the data voltage and a threshold voltage of the driving transistor, and is connected to the driving transistor through the second switching unit to supply the control voltage to the driving transistor.

2. The display device of claim 1, wherein the first switching unit comprises:

a first switching transistor connecting the control terminal and the input terminal of the driving transistor in response to the scanning signal; and

a second switching transistor connecting the capacitor to the data voltage in response to the scanning signal.

3. The display device of claim 2, wherein the first switching unit further comprises a third switching transistor supplying a common voltage to the output terminal of the driving transistor in response to the scanning signal.

4. The display device of claim 3, wherein the second switching unit comprises:

a fourth switching transistor connecting the input terminal of the driving transistor to the driving voltage in response to the emission signal; and

a fifth switching transistor connecting the capacitor and the output terminal of the driving transistor in response to the emission signal.

5. The display device of claim 4, wherein the control voltage is equal to sum of the common voltage and the threshold voltage subtracted by the data voltage.

6. The display device of claim 4, wherein the data voltage has a negative value.

7. The display device of claim 4, wherein the first to the fifth switching transistors and the driving transistor comprise amorphous silicon thin film transistors.

8. The display device of claim 4, wherein the first to the fifth switching transistors and the driving transistor comprise N type thin film transistors.

9. The display device of claim 4, wherein the light emitting element comprises an organic light emitting member.

10. The display device of claim 4, wherein the driving voltage and the light emitting element are connected by only the fourth switching transistor and the driving transistor during an emission period of the light emitting element.

11. The display device of claim 4, wherein a cut off period before an emission period of the light emitting element ensures that the first switching transistor is turned off before the fourth switching transistor is turned on in the emission period.

12. The display device of claim 4, wherein the first through fifth switching transistors are turned on during a precharging period, the fourth and fifth switching transistors are turned off and the first through third switching transistors remain on during a main charging period, the first through third switching transistors are turned off and the fourth and fifth switching transistors remain off during a cut off period, and the fourth and fifth switching transistors are, turned on and the first through third switching transistors remain off during an emission period.

13. The display device of claim 1,.wherein an output current of the light emitting element in an emission period of the light emitting element is not dependent on the threshold voltage of the driving transistor.

14. The display device of claim 13, wherein the output current of the light emitting element is ½

k (Vss—

Vdata)², where k is a constant, Vss is a common voltage, and Vdata is the data voltage.

15. The display device of claim 1, wherein the driving voltage and the light emitting element are connected by no more than two transistors during an emission period of the light emitting element.

16. The display device of claim 1, further comprising scanning lines providing the scanning signal, data lines providing the data voltage, and emission lines providing the emission signal, wherein the scanning lines and the emission lines are substantially parallel to each other, and the data lines are substantially perpendicular to the scanning lines and the emission lines.

17. A display device comprising:

a light emitting element;

a driving transistor having a first terminal connected to a first voltage, a second terminal connected to the light emitting element, and a control terminal;

a capacitor connected between the second terminal and the control terminal of the driving transistor;

a first switching element operating in response to a scanning signal and connected between the first terminal and the control terminal of the driving transistor;

a second switching element operating in response to the scanning signal and connected between the capacitor and a data voltage;

a third switching element operating in response to the scanning signal and connected between the second terminal of the driving transistor and a second voltage;

a fourth switching element operating in response to an emission signal and connected between the first voltage and the first terminal of the driving transistor; and

a fifth switching element operating in response to the emission signal and connected between the capacitor and the second terminal of the driving transistor.

18. The display device of claim 17, wherein during first to fourth periods in series,

the first to the fifth transistors turn on during the first period;

the first, the second, and the third transistors turn on and the fourth and the fifth transistors turn off during the second period;

the first to the fifth transistors turn off during the third period; and

the first, the second, and the third transistors turn off and the fourth and the fifth transistors turn on during the fourth period.

19. The display device of claim 18;

wherein the data voltage is equal to or lower than about zero.

20. A method of driving a display device including a light emitting element, a driving transistor having a control terminal, a first terminal, and a second terminal connected to the light emitting element, and a capacitor connected to the control terminal of the driving transistor, the method comprising:

connecting the control terminal and the first terminal of the driving transistor;

connecting the second terminal of the driving transistor to a common voltage;

connecting the capacitor to a data voltage;

connecting the capacitor between the control terminal and the second terminal of the driving transistor; and

connecting the first terminal of the driving transistor to a driving voltage.

21. The method of claim 20, further comprising:

applying a first voltage to the control terminal of the driving transistor to charge the capacitor.

22. The method of claim 21, further comprising:

isolating the control terminal and the first terminal of the driving transistor after connecting the control terminal and the first terminal of the driving transistor.

23. The method of claim 22, further comprising:

separating the capacitor and the driving transistor from external signal sources.

24. A method of driving a display device including a light emitting element, a driving transistor connected to the light emitting element, and a capacitor connected to the driving transistor and the light emitting element, the method comprising:

applying a first voltage and a data voltage to be charged into the capacitor;

discharging the voltage stored in the capacitor toward a second voltage through the driving transistor;

applying the voltage of the capacitor after the discharge to the driving transistor to turn on the driving transistor; and

supplying a driving current to the light emitting element through the driving transistor to emit light.

25. A display device comprising:

a light emitting element; and

,

a driving transistor supplying a driving current to the light emitting element;

wherein a change in threshold voltage of the driving transistor does not substantially affect an output current of the light emitting element during an emission period.

26. The display device of claim 25, further comprising a data line providing a data voltage, wherein the light emitting element is connected to a common voltage, and the output current of the light emitting element during the emission period is ½

k (Vss−

Vdata)², where k is a constant, Vss is the common voltage, and Vdata is the data voltage.

27. The display device of claim 25, wherein a driving voltage and the light emitting element are connected by no more than two transistors during the emission period.