Driving circuit for unit pixel of organic light emitting displays

• US 6,756,741 B2
• Filed: 03/26/2003
• Issued: 06/29/2004
• Est. Priority Date: 07/12/2002
• Status: Active Grant

• Current Assignee: AU Optronics Corporation
• Original Assignee: AU Optronics Corporation
• Inventors: Li, Chun-Huai
• Primary Examiner(s): Wong, Don
• Assistant Examiner(s): Dinh, Trinh Vo
• Application Number:
  US10/396,780
• Publication Number:
  US 20040007989A1
• Time in Patent Office: 461 Days
• Field of Search: 315/169--16, 345/92, 345/204, 345/36, 345/45, 345/46, 345/76, 345/82, 345/214
• US Class Current: 315/169.3
• CPC Class Codes: G09G 2300/0842 forming a memory circuit, e.g. a dynamic memory with one capacitor
• CPC Class Codes: G09G 2320/0233 Improving the luminance or brightness uniformity across the screen
• 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 driving circuit for an organic light emitting diode comprises the following elements. A driving transistor has a control terminal, a first electrode and a second electrode, wherein the first electrode and the second electrode are connected to a power line and the organic light emitting diode. A first switch device can be turned on by a scan signal to electrically conduct the power line and the control terminal of the driving transistor for maintaining the control terminal at the voltage level of the scan signal. And a second switch device can be turned on by the scan signal to electrically conduct a data line and the second electrode of the driving transistor for transferring the data signal to the second electrode and maintaining the second electrode at the voltage level of the data signal. Thus, by maintaining the control terminal of the driving transistor and the second electrode at the certain levels the operation current of the driving transistor will not affected by the voltage difference between two electrodes of the organic light emitting diode.

Claims

1. A driving circuit for an organic light emitting diode, said driving circuit comprises:

a driving transistor having a control terminal, a first electrode and a second electrode, wherein said first electrode and said second electrode are connected respectively to a power line and an organic light emitting diode;

a first switch device responsive to a scan signal from a scan line to electrically conduct said power line and said control terminal of said driving transistor to maintain said control terminal at a certain voltage level equal to that of said power line; and

a second switch device responsive to said scan signal from said scan line to electrically conduct a data line and said second electrode of said driving transistor and to transfer a data signal of said data line to said second electrode for maintaining said second electrode at a certain voltage level equal to that of said data signal;

wherein said control terminal and said second electrode are maintained respectively at certain voltage levels to prevent an operating current of said driving transistor from affection of a voltage difference between two terminals of said organic light emitting diode.

2. The driving circuit of claim 1, wherein said first switch device is a transistor of which a gate is connected to a scan line, a source and a drain are connected respectively to said power line and said control terminal of said driving transistor.

3. The driving circuit of claim 1, wherein said second switch device is a transistor of which a gate is connected to a scan line, a drain and a source are connected respectively to said data line and said second electrode of said driving transistor.

4. The driving circuit of claim 1, wherein said control terminal of said driving transistor is a gate, said first electrode is a drain and said second electrode is a source.

5. The driving circuit of claim 1, further comprises a storage capacitor of which two terminals are respectively connected to said gate and said source of said driving transistor.

6. A driving circuit for an organic light emitting diode, said driving circuit comprises:

a driving transistor having a gate, a source and a drain, wherein said drain is connected to a power line and said source is connected to said organic light emitting diode;

a first switch transistor has a first gate, a first drain and a first source, wherein said first gate is connected to a scan line, said first source is connected to said power line and said first drain is connected to said gate of said driving transistor, when said first switch transistor is turned on by said scan signal from said scan line, a voltage signal of said power line can turn said driving transistor on; and

a second switch transistor has a second gate, a second drain and a second source, wherein said second gate is connected to said scan line, said second drain is connected to a data line, and said second source is connected to said source of said driving transistor, when said second switch transistor is turned on by said scan signal from said scan line, a data signal of said data line is applied to said drain of said driving transistor.

7. The driving circuit of claim 6, further comprises a storage capacitor of which two terminals are respectively connected to said first drain of said first switch transistor and said second source of said second switch transistor.

8. An unit pixel circuit for an organic light emitting display comprises:

a scan line for transferring a scan signal to said unit pixel circuit;

a data line for transferring a data signal to said unit pixel circuit;

an organic light emitting diode has a positive terminal and a negative terminal, wherein said negative terminal is connected to a ground terminal;

a driving transistor has a control terminal, a first electrode and a second electrode, wherein said first electrode and said second electrode are respectively connected to a power line and said positive terminal of said organic light emitting diode;

a first switch transistor responsive to said scan signal of said scan line to electrically conduct said power line and said control terminal of said driving transistor for maintaining said control terminal at the voltage level of said scan signal; and

a second switch transistor responsive to said scan signal of said scan line to electrically conduct said data line and said second electrode of said driving transistor for maintaining said second electrode at the voltage level of said data signal;

when said first switch transistor and said second switch transistor are turned on by said scan signal, said first electrode and said second electrode of said driving transistor are conducted to transfer said data signal of said data line to said source of said driving transistor.

9. The circuit of claim 8, wherein a gate of said first switch transistor is connected to said scan line, and a source and a drain thereof are respectively connected to said power line and said control terminal of said driving transistor.

10. The circuit of claim 8, wherein a gate of said second switch transistor is connected to said scan line, a drain and a source thereof are connected respectively to said data line and said second electrode of said driving transistor.

11. The circuit of claim 8, wherein said control terminal of said driving transistor is a gate, said first electrode is a drain and said second electrode is a source.

12. The circuit of claim 8, further comprises a storage capacitor of which two terminals are connected respectively to said gate and said source of said driving transistor.