Shift register

• US 7,477,226 B2
• Filed: 05/31/2005
• Issued: 01/13/2009
• Est. Priority Date: 05/31/2004
• Status: Active Grant

• Current Assignee: LG Display Co., Ltd.
• Original Assignee: LG Display Co., Ltd.
• Inventors: Kim, Binn, Yoon, Soo Young
• Primary Examiner(s): Nguyen; Kevin M
• Application Number:
  US11/139,515
• Publication Number:
  US 20050264514A1
• Time in Patent Office: 1,323 Days
• Field of Search: 345/98, 345/100, 345/96, 345/87, 377/64, 377/68, 377/79
• US Class Current: 345/100
• CPC Class Codes: G09G 2300/0408 Integration of the drivers onto the display substrate
• CPC Class Codes: G11C 19/00 Digital stores in which the information is moved stepwise, e.g. shift registers
• CPC Class Codes: G11C 19/184 with field-effect transistors, e.g. MOS-FET
• CPC Class Codes: G11C 19/28 using semiconductor elements G11C19/14, G11C19/36 take precedence

Abstract

Disclosed is a shift register capable of mitigating gate bias stress. The shift register, including a plurality of stages, includes an output buffer having a pull-up transistor and two pull-down transistors, each with gates connected to different nodes. One of the two pull-down transistors operates during an even frame portion of an LCD operation; and the other of the two pull-down transistors operates during an odd frame portion of the LCD display operation. Alternating operation of the pull-down transistors substantially mitigates gate stress, and substantially enables the shift register to be fabricated with amorphous silicon.

Claims

1. A shift register having a plurality of stages, each stage comprising:

first, second, and third driving voltage supply lines;

at least two clock signal supply lines;

an output buffer having an output pull-up transistor and first arid second output pull-down transistors;

a first controller having an input connected to a start signal supply line and an output connected to a first node; and

a second controller having an input connected to the first and second voltage supply lines and an output connected to gates of the first and second output pull-down transistors,

wherein high voltages are alternately applied to gates of the first and second output pull-down transistors every predetermined frame;

wherein the first and second output pull-down transistors are connected to second and third nodes, respectively; and

wherein first and second driving voltages supplied to the first and second voltage supply lines have voltages alternately inverted with respect to each other every predetermined frame.

2. The shift register according to claim 1, wherein the first controller includes:

a charge transistor having a gate connected to the start signal supply line and an output connected to the first node; and

a plurality of discharge transistors connected to the first node and the third driving voltage supply line.

3. The shift register according to claim 2, wherein the first node is connected to a gate of the pull-up output transistor.

4. The shift register according to claim 2, wherein the plurality of discharge transistors includes:

a first discharge transistor having a gate connected to the second node; and

a second discharge transistor having a gate connected to the third node.

5. The shift register according to claim 4, wherein the second controller includes an odd frame voltage control transistor having a gate connected to the first driving voltage supply line and an output connected to the second node.

6. The shift register according to claim 4, wherein the second controller includes an even frame voltage control transistor having a gate connected to the third node.

7. The shift register according to claim 4, further including a third discharge control transistor having a gate connected to an output of a later stage.

8. The shift register according to claim 4, wherein the second node is connected to a gate of the first output pull-down transistor.

9. The shift register according to claim 4, wherein the third node is connected to a gate of the second output pull-down transistor.

10. The shift register according to claim 1, wherein the output pull-up transistor and the first and second output pull-down transistors include amorphous silicon.

11. The shift register according to claim 1, wherein a third driving voltages supplied to the third voltage supply lines has a low voltage.

12. The shift register according to claim 11, wherein the first and second driving voltages are changed with respect to the third driving voltage.

13. A shift register having a plurality of stages, each stage comprising:

an output buffer having a first transistor and second and third transistors, the second and third transistors having the same polarity;

a first controller for controlling an output state of the output buffer; and

a second controller for switching an output control between the second and third transistors,

wherein high voltages are alternately applied to gates of the second and third transistors every predetermined frame;

wherein the second and third transistors are connected to second and third nodes, respectively; and

wherein first and second driving voltages supplied to first and second voltage supply lines have voltages alternately inverted with respect to each other every predetermined frame.

14. The shift register according to claim 13, further comprising:

first and second voltage supply lines connected to the second controller.

15. The shift register according to claim 13, further comprising a start signal supply line connected to the first controller.

16. The shift register according to claim 13, wherein the first controller is connected to an output of a subsequent stage.

17. The shift register according to claim 13, further comprising a clock signal supply line connected to the output buffer.

18. The shift register according to claim 13, wherein the first to third transistors include amorphous silicon.