Granted Patent B1

US 7,417,882 · App. 11/525,274 · Granted Aug 26, 2008

Abstract

Claims (69)

1. A content addressable memory (CAM) device, comprising:

a plurality CAM cell groups, the CAM cells of each group being commonly connected to at least one local compare data line;

at least a first global compare data line;

a mask value circuit corresponding to each CAM cell group, each mask value circuit providing a mask value; and

at least a first logic circuit corresponding to each CAM cell group having a first input coupled to the at least first global compare data line, a second input coupled to receive the mask value of the corresponding mask value circuit, and an output coupled to the corresponding at least first local compare data line.

2. The CAM device of claim 1 , wherein:

each CAM cell comprises a binary CAM cell that includes a compare data input coupled to the local compare data line of the CAM cell group containing the CAM cell,

a storage circuit, and

a compare circuit that generates a compare result according to a comparison between a value received at the compare data input and a value stored by the storage circuit.

3. The CAM device of claim 1 , wherein:

each CAM cell comprises

a storage circuit, and

at least first and second compare transistors having source-drain paths arranged in series with one another between a match line and a discharge node, the first transistor having a gate coupled to the first local compare data line corresponding to the CAM cell group of the CAM cell, the second transistor having a gate coupled to the storage circuit.

4. The CAM device of claim 1 , further including:

the CAM cells of each group are also commonly connected to a complementary local compare data line;

a complementary global compare data line; and

a second logic circuit corresponding to each CAM cell group having a first input coupled to the complementary global compare data line, a second input coupled to receive the mask value of the corresponding local mask value circuit, and an output coupled to the corresponding complementary compare data line.

5. The CAM device of claim 4 , wherein:

each CAM cell comprises

a storage circuit, and

first and second compare transistors having source-drain paths arranged in series with one another between a match line and a discharge node, the first transistor having a gate coupled to the local compare data line corresponding to the CAM cell group of the CAM cell, the second transistor having a gate coupled to the storage circuit, and

third and fourth compare transistors having source-drain paths arranged in series with one another between a match line and the discharge node, the third transistor having a gate coupled to the local complementary compare data line corresponding to the CAM cell group of the CAM cell, the fourth transistor having a gate coupled to the storage circuit.

6. The CAM device of claim 1 , wherein:

each mask value circuit comprises a volatile storage circuit.

7. The CAM device of claim 6 , wherein:

each mask value circuit comprises a latch.

8. The CAM device of claim 1 , wherein:

each mask value circuit comprises a nonvolatile storage circuit.

9. The CAM device of claim 1 , wherein:

the at least a first logic circuit comprises an AND gate.

10. A content addressable memory (CAM) device, comprising:

at least a first global compare data line;

a plurality of local compare data line pairs, each local compare data line pair being coupled to the first global compare data line by a corresponding local compare data driver circuit;

a different mask value circuit corresponding to each local compare data line pair;

each local compare data driver circuit drives the corresponding local compare data line pair according to a logical combination of a mask value stored in the corresponding mask value circuit and at least a value on the global compare data line; and

a different group of CAM cells coupled to each local compare data line pair.

11. The CAM device of claim 10 , wherein:

each local compare data line pair includes at least a local compare data line; and

each local compare data driver circuit further includes at least a first equalization path coupled between the at least first global compare data line and the local compare data line, the first equalization path providing a low impedance path in response to a precharge signal.

12. The CAM device of claim 11 , wherein:

the at least first global compare data line further includes a complementary global compare data line;

each local compare data line pair further includes a complementary local compare data line;

each local compare data driver circuit further includes at least a second equalization path coupled between the complementary global compare data line and the complementary local compare data line, the second equalization path providing a low impedance path in response to the precharge signal.

13. The CAM device of claim 10 , further including:

a bit line corresponding to the global compare data line;

each local compare data line pair includes at least a local compare data line; and

each local compare data driver circuit further includes a bit line equalization path coupled between the at least global compare data line and the local compare data line, the bit line equalization path providing a low impedance path in response to a precharge signal.

14. The CAM device of claim 10 , wherein:

the groups of CAM cells comprise binary CAM cells, each binary CAM cell providing a compare result according to a comparison between a stored data value and a data value on the corresponding local compare data line pair.

15. The CAM device of claim 14 , wherein:

the compare result includes a high or low impedance path between a reference node a match line.

16. The CAM device of claim 10 , further including:

a global mask line corresponding to the global compare data line; and

each local compare data driver circuit drives the corresponding local compare line pair according to a logical combination of the mask value stored in the corresponding mask value circuit, the value on the global compare data line, and a value on the global mask line.

17. The CAM device of claim 16 , wherein:

each local compare data line pair includes a local compare data line and a complementary local compare data line, and

each local compare data driver circuit includes

a first logic gate having a first input coupled to the global compare data line, a second input coupled to receive the mask value of the corresponding mask value circuit, a third input coupled to the global mask line, and an output coupled to the local compare data line,

the second logic gate having a first input coupled to the global compare data line, a second input coupled to receive the mask value of the corresponding mask value circuit, a third input coupled to the global mask line, and an output coupled to the complementary local compare data line.

18. A method, comprising the steps of:

for each of a plurality of content addressable memory (CAM) cell groups, logically combining a value on at least one global compare data line with a mask value associated with the CAM cell group to generate a local compare data values for the CAM cell group; and

forcing a same match result for all CAM cells of the same CAM cell group when the local compare data values for the CAM cell group have predetermined values.

19. The method of claim 18 , wherein:

logically combining the value on at least one global bit line with a mask value associated with each different CAM cell group includes

for each CAM cell group

driving a local compare data line coupled to the CAM cell group according to the logical combination of a value on a global bit line and the associated mask value, and

driving a complementary local compare data line value coupled to the CAM cell group according to the logical combination of a value on a complementary global bit line and the associated mask value.

20. The method of claim 18 , wherein:

forcing the same match result for all CAM cells of the same CAM cell group includes, within each CAM cell of the group, creating a high impedance path between a corresponding match line and a discharge node.

Assignments (11)