METHOD OF OPERATING WRITE ASSIST CIRCUITRY

• US 20140153345A1
• Filed: 02/11/2014
• Published: 06/05/2014
• Est. Priority Date: 11/30/2010
• Status: Active Grant

• Current Assignee: Taiwan Semiconductor Manufacturing Company Limited
• Original Assignee: Taiwan Semiconductor Manufacturing Company Limited
• Inventors: KIM, Young Seog, KIM, Young Suk
• Granted Patent: US 9,269,424 B2
• Time in Patent Office: Days
• US Class Current: 365/189.11
• CPC Class Codes: G11C 11/419 Read-write [R-W] circuits
• CPC Class Codes: G11C 8/08 Word line control circuits, e.g. drivers, boosters, pull-up circuits, pull-down circuits, precharging circuits, for word lines

Abstract

A method includes causing, by a first circuit, a first signal transition at a first node based on a clock signal. A first edge, from a first level to a second level, of a word line signal is generated responsive to the first signal transition. A second signal transition at a second node is caused by a second circuit based on the clock signal. The second circuit and the first circuit are configured to cause the second signal transition to occur later than the first signal transition by a delay time. A first edge, from a third logic level to a fourth level, of a tracking word line signal is generated responsive to the second signal transition.

Claims

1. A method comprising:

generating a first pull up current at a first node in a word line driver circuit; and

generating a second pull up current at a second node in a tracking word line driver circuit,

wherein

the second pull up current is higher than the first pull up current;

when the first node is at a first node high logic level, a word line generated by the word line driver circuit is at a word line low logic level, and when the first node is at a first node low logic level, the word line is at a word line high logic level; and

when the second node is at a second node high logic level, a tracking word line generated by the tracking word line driver is at a tracking word line low logic level, and when the second node is at a second node low logic level, the tracking word line is at a tracking word line high logic level.

2. The method of claim 1, further comprising:

driving a first PMOS transistor having a first drain coupled to the first node to generate the first pull up current at the first node; and

driving a second PMOS transistor having a second drain coupled to the second node to generate the second pull up current at the second node, the first PMOS transistor having a first size smaller than a second size of the second PMOS transistor.

3. The method of claim 1, further comprising:

driving a first PMOS transistor having a first drain coupled to the first node to generate the first pull up current at the first node; and

driving a second PMOS transistor having a second drain coupled to the second node and a third PMOS transistor having a third drain coupled to the second node, to generate the second pull up current at the second node;

the first PMOS transistor having a first size substantially about the same size as a second size of the second PMOS transistor.

4. The method of claim 3, further comprising driving a fourth transistor coupled in series with the third PMOS transistor to turn on or to turn off the third PMOS transistor.

5. The method of claim 1, further comprising:

driving a first PMOS transistor having a first drain coupled to the first node to generate the first pull up current at the first node; and

driving a first circuit coupled to the second node to generate the second pull up current at the second node,

wherein the first circuit includes

a second PMOS transistor having a second drain coupled to the second node,

a third PMOS transistor having a third drain coupled to a second source of the second PMOS transistor, and

a fourth PMOS transistor having a fourth drain coupled to the third drain.

6. The method of claim 1, further comprising:

driving a first PMOS transistor having a first drain coupled to the first node to generate the first pull up current at the first node; and

driving a first circuit coupled to the second node to generate the second pull up current at the second node,

wherein

the first circuit includes a second transistor having a second gate, a second drain, and a second source;

a third transistor having a third gate, a third drain, and a third source;

a fourth transistor having a fourth gate, a fourth drain, and a fourth source; and

a fifth transistor having a fifth gate, a fifth drain, and a fifth source;

the second drain is coupled to the second node;

the second source is coupled to the third drain and the fourth drain;

the second gate is coupled to the third gate and the fourth gate; and

the fourth source is coupled to the fifth drain.

7. A method comprising:

causing, by a first circuit, a transition at a first node from a first node high logic level to a first node low logic level, thereby generating a transition of a word line signal from a word line low logic level to a word line high logic level;

causing, by a second circuit, a transition at a second node from a second node high logic level to a second node low logic level, thereby generating a transition of a tracking word line signal from a tracking word line low logic level to a tracking word line high logic level;

generating a further transition of the word line signal from the word line high logic level to the word line low logic level, thereby generating a word line pulse width; and

generating a further transition of the tracking word line signal from the tracking word line high logic level to the tracking word line low logic level, thereby generating a tracking word line pulse width,

wherein

the second circuit is configured to have pull-up driving capability greater than that of the first circuit;

the transition of the tracking word line signal from the tracking word line low logic level to the tracking word line high logic level is later than the transition of the word line signal from the word line low logic level to the word line high logic level by a delay time; and

the word line pulse width is larger than the tracking word line pulse width.

8. The method of claim 7, further comprising causing the delay time by providing a first pull up current at the first node by the first circuit and providing a second pull up current at the second node by the second circuit, and the second pull up current is greater than the first pull up current.

9. The method of claim 8, wherein the causing the delay time is performed in a write operation of a memory cell coupled to receive the word line signal.

10. The method of claim 7, wherein the causing at the second node the transition from the second node high logic level to the second node low logic level comprises:

biasing a gate of a first transistor of the second circuit by the tracking word line signal; and

biasing a gate of a second transistor of the second circuit by the tracking word line signal.

11. The method of claim 7, wherein the causing at the second node the transition from the second node high logic level to the second node low logic level comprises:

biasing a gate of a first transistor of the second circuit by the tracking word line signal;

turning on a second transistor of the second circuit between a third transistor of the second circuit and the second node responsive to a control signal; and

biasing a gate of the third transistor of the second circuit by the tracking word line signal.

12. The method of claim 11, wherein the first transistor of the second circuit is biased to provide a current substantially the same as the first pull up current.

13. The method of claim 7, wherein the causing at the second node the transition from the second node high logic level to the second node low logic level comprises:

biasing a gate of a first transistor of the second circuit by the tracking word line signal;

biasing a gate of a second transistor of the second circuit by the tracking word line signal, the first and second transistor being connected in series between a power node and the second node; and

turning on a third transistor of the second circuit between the power node and the second transistor responsive to a control signal.

14. A method comprising:

causing, by a first circuit, a first signal transition at a first node based on a clock signal;

generating a first edge, from a first level to a second level, of a word line signal responsive to the first signal transition;

causing, by a second circuit, a second signal transition at a second node based on the clock signal, the second circuit and the first circuit being configured to cause the second signal transition to occur later than the first signal transition by a delay time; and

generating a first edge, from a third logic level to a fourth level, of a tracking word line signal responsive to the second signal transition.

15. The method of claim 14, further comprising:

generating a second edge, from the second level to the first level, of the word line signal; and

generating a second edge, from the fourth level to the third level, of the tracking word line signal.

16. The method of claim 15, wherein the generating the second edge of the word line signal and the generating the second edge of the tracking word line signal occur at about the same time.

17. The method of claim 15, wherein the first edge and second edge of the word line signal defines a word line pulse width;

the first edge and second edge of the tracking word line signal defines a tracking word line pulse width; and

the word line pulse width is larger than the tracking word line pulse width.

18. The method of claim 14, wherein

the causing the first signal transition at the first node comprises:

providing a first current configured to pull a voltage level of the first node along a direction opposite a direction of the first signal transition;

the causing the second signal transition at the second node comprises;

providing a second current configured to pull the voltage level of the second node along a direction opposite the direction of the second signal transition; and

the second current is greater than the first current.

19. The method of claim 18, wherein

the providing the first current is performed by biasing a gate of a transistor of the first circuit by the word line signal;

and

the providing the second current is performed by biasing a gate of a transistor of the second circuit by the tracking word line signal, the transistor of the second circuit having a size greater than the transistor of the first circuit.

20. The method of claim 18, wherein

the providing the first current is performed by biasing a gate of a transistor of the first circuit by the word line signal;

and

the providing the second current is performed by biasing gates of a first transistor and a second transistor of the second circuit by the tracking word line signal, the first transistor of the second circuit having a size substantially the same as the transistor of the first circuit.