Shift register and display apparatus

1. A shift register, comprising:

a pre-charge unit configured to receive a first input signal and a second input signal and to output a pre-charge signal via a first node based on the first input signal and the second input signal, wherein the pre-charge unit comprises:

a first transistor, wherein a gate of the first transistor is configured to receive a scan signal outputted by a previous four stage shift register, a first source/drain of the first transistor is configured to receive a forward input signal, and a second source/drain of the first transistor is configured to output the pre-charge signal; and

a second transistor, wherein a gate of the second transistor is configured to receive a scan signal outputted by a next four stage shift register, a first source/drain of the second transistor is configured to receive a backward input signal, and a second source/drain of the second transistor is coupled to the second source/drain of the first transistor;

a pull-up unit coupled to the pre-charge unit, the pull-up unit configured to receive the pre-charge signal and a clock signal and to output a scan signal via a second node based on the pre-charge signal and the clock signal;

a first pull-down unit coupled to the pre-charge unit and the pull-up unit, the first pull-down unit configured to receive the pre-charge signal, a first pull-down control signal and a second pull-down control signal and to control whether to pull down the scan signal to a first reference voltage level based on the pre-charge signal, the first pull-down control signal and the second pull-down control signal; and

a second pull-down unit coupled to the pre-charge unit and the pull-up unit, the second pull-down unit configured to receive the pre-charge signal, the first pull-down control signal and the second pull-down control signal and to control whether to keep the scan signal at the first reference voltage level based on the pre-charge signal, the first pull-down control signal and the second pull-down control signal;

wherein a duty cycle of the clock signal is less than 50 percent.

2. The shift register of claim 1 , wherein a high level duration of the clock signal is half of a clock period of the clock signal subtracted by a data writing period.

3. The shift register of claim 1 , wherein the pull-up unit comprises:

a third transistor, wherein a gate of the third transistor is configured to receive the pre-charge signal, a first source/drain of the third transistor is configured to receive the clock signal, and a second source/drain of the third transistor is configured to output the scan signal; and

a capacitor, wherein a first terminal of the capacitor is coupled to the gate of the third transistor, and a second terminal of the capacitor is coupled to the second source/drain of the third transistor.

4. The shift register of claim 1 , wherein the first pull-down unit comprises:

a fourth transistor, wherein a gate and a first source/drain of the fourth transistor are configured to input the first pull-down control signal;

a fifth transistor, wherein a gate of the fifth transistor is configured to input the second pull-down control signal, a first source/drain of the fifth transistor is configured to input the first reference voltage level, and a second source/drain of the fifth transistor is coupled to the second source/drain of the fourth transistor;

a sixth transistor, wherein a gate of the sixth transistor is coupled to the first node, a first source/drain of the sixth transistor is configured to input the first reference voltage level, and a second source/drain of the sixth transistor is coupled to the second source/drain of the fourth transistor;

a seventh transistor, wherein a gate of the seventh transistor is coupled to the second source/drain of the sixth transistor, a first source/drain of the seventh transistor is configured to input the first reference voltage level, and a second source/drain of the seventh transistor is coupled to the first node; and

an eighth transistor, wherein a gate of the eighth transistor is coupled to the second source/drain of the sixth transistor, a first source/drain of the eighth transistor is configured to input a second reference voltage level, and a second source/drain of the eighth transistor is coupled to the second node.

5. The shift register of claim 4 , wherein the second reference voltage level is substantially lower than the first reference voltage level.

6. The shift register of claim 5 , wherein a difference between the second reference voltage level and the first reference voltage level is substantially 3 volts.

7. The shift register of claim 1 , wherein the second pull-down unit comprises:

a ninth transistor, wherein a gate and a first source/drain of the ninth transistor are configured to input the second pull-down control signal;

a tenth transistor, wherein a gate of the tenth transistor is configured to input the first pull-down control signal, a first source/drain of the tenth transistor is configured to input the first reference voltage level, and a second source/drain of the tenth transistor is coupled to the second source/drain of the ninth transistor;

an eleventh transistor, wherein a gate of the eleventh transistor is coupled to the first node, a first source/drain of the eleventh transistor is configured to input the first reference voltage level, and a second source/drain of the eleventh transistor is coupled to the second source/drain of the ninth transistor;

a twelfth transistor, wherein a gate of the twelfth transistor is coupled to the second source/drain of the eleventh transistor, a first source/drain of the twelfth transistor is configured to input the first reference voltage level, and a second source/drain of the twelfth transistor is coupled to the first node; and

a thirteenth transistor, wherein a gate of the thirteenth transistor is coupled to the second source/drain of the eleventh transistor, a first source/drain of the thirteenth transistor is configured to input a second reference voltage level, and a second source/drain of the thirteenth transistor is coupled to the second node.

8. The shift register of claim 7 , wherein the second reference voltage level is substantially lower than the first reference voltage level.

9. The shift register of claim 8 , wherein a difference between the second reference voltage level and the first reference voltage level is substantially 3 volts.

10. A display apparatus, comprising:

a display panel; and

a gate driver configured to drive the display apparatus and having 1 st -N th stage shift registers, wherein the i th stage shift register of the 1 st -N th stage shift registers comprises:

a pre-charge unit configured to receive a first input signal and a second input signal and output a pre-charge signal via a first node based on the first input signal and the second input signal, wherein the pre-charge unit of the i th stage shift register comprises:

a first transistor, wherein a gate of the first transistor is configured to receive a first input signal, a first source/drain of the first transistor is configured to receive a forward input signal, and a second source/drain of the first transistor is configured to output the pre-charge signal; and

a second transistor, wherein a gate of the second transistor is configured to receive a second input signal, a first source/drain of the second transistor is configured to receive a backward input signal, and a second source/drain of the second transistor is coupled to the second source/drain of the first transistor, wherein:

when i is from 1 to 4, the first input signal is a starting signal, and the second input signal is an (i+4) th stage scan signal outputted by the (i+4) th stage shift register of the 1 st -N th stage shift registers;

when i is from (N−3) to N, the first input signal is an (i−4) th stage scan signal outputted by the (i−4) th stage shift register of the 1 st -N th stage shift registers, and the second input signal is an ending signal;

when i is from 5 to (N−4), the first input signal is an (i−4) th stage scan signal outputted by the (i−4) th stage shift register of the 1 st -N th stage shift registers, and the second input signal is an (i+4) th stage scan signal outputted by the (i+4) th stage shift register of the 1 st -N th stage shift registers;

a pull-up unit that is coupled to the pre-charge unit, the pull-up unit configured to receive the pre-charge signal and a clock signal and output an i th stage scan signal via a second node based on the pre-charge signal and the clock signal;

a first pull-down unit coupled to the pre-charge unit and the pull-up unit, the first pull-down unit configured to receive the pre-charge signal, a first pull-down control signal and a second pull-down control signal and control whether to pull down the i th stage scan signal to a first reference voltage level based on the pre-charge signal, the first pull-down control signal and the second pull-down control signal; and

a second pull-down unit coupled to the pre-charge unit and the pull-up unit, the second pull-down unit configured to receive the pre-charge signal, the first pull-down control signal and the second pull-down control signal and control whether to keep the i th stage scan signal at the first reference voltage level based on the pre-charge signal, the first pull-down control signal and the second pull-down control signal;

wherein a duty cycle of the clock signal is less than 50 percent.

11. The display apparatus of claim 10 , wherein a high level duration of the clock signal is half of a clock period of the clock signal subtracted by a data writing period.

12. The display apparatus of claim 10 , wherein the pull-up unit of the i th stage shift register comprises:

a third transistor, wherein a gate of the third transistor is configured to receive the pre-charge signal, a first source/drain of the third transistor is configured to receive the clock signal, and a second source/drain of the third transistor is configured to output the i th stage scan signal; and

a capacitor, wherein a first terminal of the capacitor is coupled to the gate of the third transistor, and a second terminal of the capacitor is coupled to the second source/drain of the third transistor.

13. The display apparatus of claim 10 , wherein the first pull-down unit of the i th stage shift register comprises:

a fourth transistor, wherein a gate and a first source/drain of the fourth transistor are configured to input the first pull-down control signal;

a fifth transistor, wherein a gate of the fifth transistor is configured to input the second pull-down control signal, a first source/drain of the fifth transistor is configured to input the first reference voltage level, and a second source/drain of the fifth transistor is coupled to the second source/drain of the fourth transistor;

a sixth transistor, wherein a gate of the sixth transistor is coupled to the first node, a first source/drain of the sixth transistor is configured to input the first reference voltage level, and a second source/drain of the sixth transistor is coupled to the second source/drain of the fourth transistor;

a seventh transistor, wherein a gate of the seventh transistor is coupled to the second source/drain of the sixth transistor, a first source/drain of the seventh transistor is configured to input the first reference voltage level, and a second source/drain of the seventh transistor is coupled to the first node; and

an eighth transistor, wherein a gate of the eighth transistor is coupled to the second source/drain of the sixth transistor, a first source/drain of the eighth transistor is configured to input a second reference voltage level, and a second source/drain of the eighth transistor is coupled to the second node;

wherein the second reference voltage level is substantially lower than the first reference voltage level.

14. The display apparatus of claim 13 , wherein a difference between the second reference voltage level and the first reference voltage level is substantially 3 volts.

15. The display apparatus of claim 10 , wherein the second pull-down unit of the i th stage shift register comprises:

a ninth transistor, wherein a gate and a first source/drain of the ninth transistor are configured to input the second pull-down control signal;

a tenth transistor, wherein a gate of the tenth transistor is configured to input the first pull-down control signal, a first source/drain of the tenth transistor is configured to input the first reference voltage level, and a second source/drain of the tenth transistor is coupled to the second source/drain of the ninth transistor;

an eleventh transistor, wherein a gate of the eleventh transistor is coupled to the first node, a first source/drain of the eleventh transistor is configured to input the first reference voltage level, and a second source/drain of the eleventh transistor is coupled to the second source/drain of the ninth transistor;

a twelfth transistor, wherein a gate of the twelfth transistor is coupled to the second source/drain of the eleventh transistor, a first source/drain of the twelfth transistor is configured to input the first reference voltage level, and a second source/drain of the twelfth transistor is coupled to the first node; and

a thirteenth transistor, wherein a gate of the thirteenth transistor is coupled to the second source/drain of the eleventh transistor, a first source/drain of the thirteenth transistor is configured to input a second reference voltage level, and a second source/drain of the thirteenth transistor is coupled to the second node;

wherein the second reference voltage level is substantially lower than the first reference voltage level.

16. The display apparatus of claim 15 , wherein a difference between the second reference voltage level and the first reference voltage level is substantially 3 volts.