Word line driver circuit for a static random access memory and method therefor
View Patent ↗A static random access memory ( 14 ) has a normal mode of operation and a low voltage mode of operation. A memory array ( 15 ) includes memory cells ( 16 ) coupled to a first power supply node (V DD ) for receiving a power supply voltage. A plurality of word line drivers is coupled to word lines of the memory array ( 15 ) and to a second power supply node ( 37 ). A word line driver voltage reduction circuit ( 36 ) has an input coupled to the first power supply node (V DD ) and an output coupled to the second power supply node ( 37 ) for reducing a voltage on the output in relation to a voltage on the input in response to a low power supply voltage signal, and thus improving a static noise margin of the memory cells ( 16 ).
1. A circuit, comprising:
a memory array comprising memory cells coupled to a first power supply node for receiving a power supply voltage, to word lines, and to bit lines;
a plurality of word line drivers coupled to the word lines and to a second power supply node; and
a voltage reduction circuit having an input coupled to the first power supply node and an output coupled to the second power supply node for reducing a voltage on the output in relation to a voltage on the input in response to a low supply voltage signal, wherein the low supply signal indicates that the power supply voltage is reduced.
2. The circuit of claim 1 , wherein the voltage reduction circuit comprises:
a first transistor that is decoupled from between the first power supply node and the second supply node in response to the low supply signal being active; and
a second transistor that is coupled between the first power supply node and the second power supply node when the low supply signal is active.
3. The circuit of claim 2 , wherein the first transistor is a P channel transistor and the second transistor is an N channel transistor.
4. The circuit of claim 3 , further comprising a fuse block circuit comprising a blown fuse, wherein the fuse block circuit has an output coupled to the second transistor.
5. The circuit of claim 4 , further comprising:
a register coupled to the second transistor; and
a central processing unit coupled to the register.
6. The circuit of claim 1 , further comprising:
a fuse block circuit comprising a plurality of fuses and coupled to the voltage reduction circuit; and
a register coupled to the voltage reduction circuit; and
a central processing unit coupled to the register.
7. The circuit of claim 6 , wherein the voltage reduction circuit comprises a plurality of transistors in which each of the plurality of transistors is coupled to a corresponding fuse of the plurality of fuses.
8. The circuit of claim 7 , wherein a fuse of the plurality of fuses is blown and the transistor that corresponds to the blown fuse is conductive in response to the blown fuse being blown.
9. The circuit of claim 1 , wherein:
the memory cells are characterized as being static random access memory cells that have a static noise margin that is increased by the voltage reduction circuit reducing the voltage on the output in relation to the voltage on the input.
10. The circuit of claim 9 , wherein the voltage reduction circuit comprises:
a first transistor that is decoupled from between the first power supply node and the second supply node in response to the low supply signal being active; and
a second transistor that is coupled between the first power supply node and the second power supply node when the low supply signal is active.
11. A circuit having a normal mode of operation and a reduced power mode of operation in which a power supply voltage is reduced, the reduced power mode of operation being indicated by a low supply voltage signal, comprising:
a memory array having memory cells coupled to a first power supply node for receiving the power supply voltage, to word lines, and to bit lines; and
word line driver means, coupled to the word lines, for providing the voltage applied to the first power supply node during the normal mode of operation and for providing a voltage reduced below the voltage applied to the first power supply node during the reduced power mode of operation.
12. The circuit of claim 11 , wherein the word line driver means comprises:
a plurality of word line drivers coupled between the word lines and a second power supply node;
a first transistor that is decoupled from between the first power supply node and the second power supply node in response to the low supply signal being active; and
a second transistor that is coupled between the first power supply node and the second power supply node when the low supply signal is active.
13. The circuit of claim 12 , wherein the first transistor is a P channel transistor and the second transistor is an N channel transistor.
14. The circuit of claim 13 , further comprising a fuse block circuit comprising a blown fuse, wherein the fuse block circuit has an output coupled to the second transistor.
15. The circuit of claim 14 , further comprising:
a register coupled to the second transistor; and
a central processing unit coupled to the register.
16. The circuit of claim 11 , further comprising:
a fuse block circuit comprising a plurality of fuses and coupled to the word line driver means;
a register coupled to the word line driver means; and
a central processing unit coupled to the register.
17. The circuit of claim 16 , wherein the word line driver means comprises a plurality of transistors in which each of the plurality of transistors is coupled to a corresponding fuse of the plurality of fuses.
18. The circuit of claim 17 , wherein a fuse of the plurality of fuses is blown and the transistor that corresponds to the blown fuse is conductive in response to the blown fuse being blown.
19. The circuit of claim 11 , wherein:
the memory cells are characterized as being static random access memory cells that have a static noise margin that is increased by the word line driver means providing a voltage reduced below the voltage applied to the first power supply node.
20. The circuit of claim 19 , wherein the word line driver means comprises:
a plurality of word line drivers coupled between the word lines and a second power supply node;
a first transistor that is decoupled from between the first power supply node and the second supply node in response to the low supply signal being active; and
a second transistor that is coupled between the first power supply node and the second power supply node when the low supply signal is active.
21. A circuit, comprising:
a memory array having memory cells coupled to a first power supply node for receiving the power supply voltage, to word lines, and to bit lines;
a plurality of word line drivers coupled to the word lines and to a second power supply node; and
voltage control means coupled to the first power supply node and the second power supply node for providing the first supply voltage to the second power supply node in a normal mode of operation and in response to entering a second mode of operation in which the power supply voltage is reduced, providing a voltage on the second power supply node which is lower than that provided on the first power supply node during the second mode of operation.
22. The circuit of claim 21 , wherein the voltage control comprises:
a first transistor that is decoupled from between the first power supply node and the second supply node in response to entering the second mode of operation; and
a second transistor that is coupled between the first power supply node and the second power supply node during the second mode of operation.
23. The circuit of claim 22 , wherein the first transistor is a P channel transistor and the second transistor is an N channel transistor.
24. The circuit of claim 23 , further comprising a fuse block circuit comprising a blown fuse, wherein the fuse block circuit has an output coupled to the second transistor.
25. The circuit of claim 24 , further comprising:
a register coupled to the second transistor; and
a central processing unit coupled to the register.
26. The circuit of claim 21 , further comprising:
a fuse block circuit comprising a plurality of fuses and coupled to the voltage control means;
a register coupled to the voltage control means; and
a central processing unit coupled to the register.
27. The circuit of claim 26 , wherein the voltage control means comprises a plurality of transistors in which each of the plurality of transistors is coupled to a corresponding fuse of the plurality of fuses.
28. The circuit of claim 27 , wherein a fuse of the plurality of fuses is blown and the transistor that corresponds to the blown fuse is conductive in response to the blown fuse being blown.
29. The circuit of claim 21 , wherein:
the memory cells are characterized as being static random access memory cells that have a static noise margin that is increased by the voltage control means reducing the voltage on the second power supply node in response to entering the second mode of operation.
30. The circuit of claim 29 , wherein the voltage control means comprises:
a first transistor that is decoupled from between the first power supply node and the second supply node in response to entering the second mode of operation; and
a second transistor that is coupled between the first power supply node and the second power supply node during the second mode of operation.
31. A method of operating a memory comprising:
a memory array having memory cells coupled to a first power supply node for receiving the power supply voltage, to word lines, and to bit lines; and
a plurality of word line drivers coupled to the word lines and to a second power supply node;
the method comprising:
during a first mode of operation, applying voltages that are substantially equal to a first level to the first power supply node and the second power supply node; and
during a second mode of operation in which the voltage applied to the first power supply node is at a second level, in which the second level is lower than the first level, applying a voltage to the second power supply node that is lower than the second level.
32. The method of claim 31 , wherein the step of applying a voltage to the second power supply node that is lower than the second level comprises decoupling a first transistor from between the first power supply node and the second power supply node while having a second transistor coupled between the first power supply node and the second power supply node.
33. The method of claim 32 , wherein the first transistor is a P channel transistor and the second transistor is an N channel transistor.
34. The method of claim 31 , wherein the memory cells are further characterized as being static random access memory cells that have a static noise margin and the step of applying a voltage to the second power supply node that is lower than the second level is further characterized as increasing the static noise margin.
35. The method of claim 31 , wherein the step of applying a voltage to the second power supply node that is lower than the second level is further characterizing as selecting among a plurality of voltage levels that are below the second level.