[PIXEL STRUCTURE OF DISPLAY AND DRIVING METHOD THEREOF]

• US 20050105031A1
• Filed: 03/29/2004
• Published: 05/19/2005
• Est. Priority Date: 11/13/2003
• Status: Active Grant

• Current Assignee: HannStar Display Corporation
• Original Assignee: HannStar Display Corporation
• Inventors: SHIH, PO-SHENG, YANG, KEI-HSIUNG
• Granted Patent: US 7,045,821 B2
• Time in Patent Office: Days
• US Class Current: 349/139
• CPC Class Codes: G09G 2300/0465 Improved aperture ratio, e.g. by size reduction of the pixel circuit, e.g. for improving the pixel density or the maximum displayable luminance or brightness
• 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 2300/0866 by means of changes in the pixel supply voltage
• CPC Class Codes: G09G 2320/043 Preventing or counteracting the effects of ageing
• CPC Class Codes: G09G 3/3233 with pixel circuitry controlling the current through the light-emitting element

Abstract

A pixel structure of a display and a driving method thereof are disclosed. The pixel structure disclosed in the invention includes a structure with less elements than that of prior art. The driving method thereof is also much easier than that of prior art. The pixel structure and driving method thereof can completely compensate the variations of the threshold voltage of a driving transistor thereof. The pixel structure includes a switching transistor, a driving transistor, a capacitor, a light emitting diode (LED) and a reset transistor.

Claims

1. A pixel structure of a display, comprising:

a switching transistor, wherein a gate terminal of the switching transistor is electrically connected to a scan line, and a source terminal thereof is electrically connected to a signal line;

a driving transistor, wherein a gate terminal of the driving transistor is electrically connected to a drain terminal of the switching transistor;

a first capacitor disposed between the gate terminal of the driving transistor and a source terminal thereof;

a light emitting diode having a first terminal electrically connected to a operational voltage, and a second terminal electrically connected to a drain terminal of the driving transistor; and

a reset transistor, wherein a gate terminal of the reset transistor is electrically connected to an autozero signal, a drain terminal is electrically connected to the driving transistor, and a source terminal electrically connected to a ground voltage.

2. The pixel structure of a display of claim 1, wherein the switching transistor, the driving transistor and the reset transistor are thin film transistors.

3. The pixel structure of a display of claim 2, wherein the switching transistor, the driving transistor and the reset transistor are made from poly-silicon.

4. The pixel structure of a display of claim 2, wherein the switching transistor, the driving transistor and the reset transistor are made from amorphous silicon.

5. The pixel structure of a display of claim 1, wherein the first terminal of the light emitting diode is an anode, and the second terminal thereof is a cathode.

6. The pixel structure of a display of claim 1, wherein the light emitting diode is made from an organic material.

7. The pixel structure of a display of claim 1, further comprising a second capacitor disposed between the source terminal and the drain terminal of the reset transistor.

8. A pixel structure of a display, comprising:

a switching transistor, wherein a gate terminal of the switching transistor is electrically connected to a scan line, and a source terminal thereof is electrically connected to a signal line;

a driving transistor, wherein a gate terminal of the driving transistor is electrically connected to a drain terminal of the switching transistor;

a first capacitor disposed between the gate terminal of the driving transistor and a source terminal thereof;

a light emitting diode having a second terminal electrically connected to a ground voltage, and a first terminal electrically connected to a source terminal of the driving transistor; and

a reset transistor, wherein a gate terminal of the reset transistor is electrically connected to an autozero signal, a source terminal is electrically connected to the driving transistor, and a drain terminal electrically connected to an operational voltage.

9. The pixel structure of a display of claim 8, wherein the switching transistor, the driving transistor and the reset transistor are thin film transistors.

10. The pixel structure of a display of claim 9, wherein the switching transistor, the driving transistor and the reset transistor are made from poly-silicon.

11. The pixel structure of a display of claim 9, wherein the switching transistor, the driving transistor and the reset transistor are made from amorphous silicon.

12. The pixel structure of a display of claim 8, wherein the first terminal of the light emitting diode is an anode, and the second terminal thereof is a cathode.

13. The pixel structure of a display of claim 8, wherein the light emitting diode is made from an organic material.

14. The pixel structure of a display of claim 8, further comprising a second capacitor disposed between the first terminal and the second terminal of the light emitting diode.

15. A driving method of a pixel of a display, adapted for a pixel structure, wherein the pixel structure comprises:

a switching transistor, a driving transistor, a first capacitor, a light emitting diode and a reset transistor, a gate terminal of the driving transistor electrically connected to a drain terminal of the switching transistor, the first capacitor disposed between the gate terminal of the driving transistor and a source terminal thereof, the light emitting diode having a first terminal electrically connected to a operational voltage, and a second terminal electrically connected to a drain terminal of the driving transistor, a drain terminal the reset transistor electrically connected to the driving transistor, and a source terminal thereof electrically connected to a ground voltage, the driving method comprising;

turning on the switching transistor at a threshold voltage writing timing, then turning off the reset transistor and applying a start voltage to the gate terminal of the driving transistor;

lowering the operational voltage to a low voltage at an data writing timing for turning off the light emitting diode, applying an data voltage to the gate terminal of the driving transistor; and

turning off the switching transistor after the data writing timing, raising the operational voltage to a high voltage, turning on the reset transistor for driving the light emitting diode.

16. The driving method of a pixel of a display of claim 15, wherein a gate terminal of the switching transistor is electrically connected to a scan line, a source terminal thereof is electrically connected to a signal line, a drain terminal thereof is electrically connected to the gate terminal of the driving transistor, and the step of turning on the switching transistor is by inputting a scan voltage via the scan line.

17. The driving method of a pixel of a display of claim 16, wherein the start voltage and the data voltage are applied to the gate terminal of the switching terminal via the signal line.

18. The driving method of a pixel of a display of claim 16, wherein the reset transistor is turned off after a delay time, when the switching transistor is turned on by the scanning voltage via the scan line;

and the delay time is determined by a time of tuning on the switching transistor.

19. The driving method of a pixel of a display of claim 15, wherein the gate terminal of the reset transistor is electrically connected to an autozero line.

20. The driving method of a pixel of a display of claim 15, wherein the first terminal of the light emitting diode is an anode, and the second terminal thereof is a cathode.

21. The driving method of a pixel of a display of claim 15, wherein the start voltage Vo is applied to the gate terminal of the driving transistor so that a gate voltage thereof is Vo;

and a source voltage is Vo−

V_T, wherein the V_T is a threshold voltage of the driving transistor.

22. The driving method of a pixel of a display of claim 21, wherein the data voltage Vdata is applied to the gate terminal of the driving transistor so that a voltage drop on the first capacitor is Vdata−

(Vo−

V_T+Δ

Vdata), wherein the Δ

Vdata=K(Vdata−

Vo).

23. The driving method of a pixel of a display of claim 22, wherein the a driving current of the light emitting diode is proportional to (Vdata−

Vo−

Δ

Vdata)².

24. The driving method of a pixel of a display of claim 22, wherein K=Cs/Ctotal, Cs represents a capacitance of the first capacitor, and Ctotal is a sum of capacitances on the source terminal of the driving transistor.

25. The driving method of a pixel of a display of claim 24, wherein the pixel structure further comprises a second capacitor disposed between the source terminal and the drain terminal of the reset transistor for adjusting the K.

26. A driving method of a pixel of a display, adapted for a pixel structure, wherein the pixel structure comprises:

a switching transistor, a driving transistor, a first capacitor, a light emitting diode and a reset transistor, a gate terminal of the driving transistor electrically connected to a drain terminal of the switching transistor, the first capacitor disposed between the gate terminal of the driving transistor and a source terminal thereof, the light emitting diode having a first terminal electrically connected to a source terminal of the driving transistor, and a second terminal electrically connected to a ground voltage, a source terminal of the reset transistor electrically connected to the driving transistor, and a drain terminal thereof electrically connected to an operational voltage, the driving method comprising;

turning on the switching transistor at a threshold voltage writing timing, then raising the ground voltage to a high voltage for turning off the light emitting diode and applying a start voltage to the gate terminal of the driving transistor;

turning off the reset transistor at an data writing timing, and applying an data voltage to the gate terminal of the driving transistor; and

turning off the switching transistor after the data writing timing, lowering the ground voltage to a low voltage for driving the light emitting diode, and turning on the reset transistor.

27. The driving method of a pixel of a display of claim 26, wherein a gate terminal of the switching transistor is electrically connected to a scan line, a source terminal thereof is electrically connected to a signal line, a drain terminal thereof is electrically connected to the gate terminal of the driving transistor, and the step of turning on the switching transistor is by inputting a scan voltage via the scan line.

28. The driving method of a pixel of a display of claim 27, wherein the start voltage and the data voltage are applied to the gate terminal of the driving transistor via the signal line.

29. The driving method of a pixel of a display of claim 27, wherein the ground voltage is raised to the high voltage after a delay time, when the switching transistor is turned on by the scanning voltage via the scan line;

and the delay time is determined by a time of tuning on the switching transistor.

30. The driving method of a pixel of a display of claim 26, wherein the gate terminal of the reset transistor is electrically connected to an autozero line.

31. The driving method of a pixel of a display of claim 26, wherein the first terminal of the light emitting diode is an anode, and the second terminal thereof is a cathode.

32. The driving method of a pixel of a display of claim 26, wherein the start voltage Vo is applied to the gate terminal of the driving transistor so that a gate voltage thereof is Vo;

and a source voltage is Vo−

V_T, wherein the V_T is a threshold voltage of the driving transistor.

33. The driving method of a pixel of a display of claim 32, wherein the data voltage Vdata is applied to the gate terminal of the driving transistor so that a voltage drop on the first capacitor is Vdata−

(Vo−

V_T+Δ

Vdata), wherein the Δ

Vdata=K(Vdata−

Vo).

34. The driving method of a pixel of a display of claim 33, wherein the a driving current of the light emitting diode is proportional to (Vdata−

Vo−

Δ

Vdata)².

35. The driving method of a pixel of a display of claim 33, wherein K=Cs/Ctotal, Cs represents a capacitance of the first capacitor, and Ctotal is a sum of capacitances on the source terminal of the driving transistor.

36. The driving method of a pixel of a display of claim 35, wherein the pixel structure further comprises a second capacitor disposed between the first terminal and the second terminal of the light emitting diode for adjusting the K.