Sibercore Technologies, Inc.

Core Networks L.l.c.

Nortel Networks Corporation

Radu Avramescu

Jason Edward Podaima

G F Randall Gibson

Sanjay Gupta

Randall Gibson

Liviu Calin

An invention is provided for lowLowpower searching in a CAMusingusessample words to save power in the compare lines.The inventionA methodincludes comparing a sample section of stored data to a corresponding sample section of search data on a plurality of rows in the CAM. If a sample section of the stored data on any row of the plurality of rows is equivalent to the corresponding sample section of the search data, a remaining section of search data is allowed to propagate to the local compare lines coupled to the remaining section of the stored data of each row. However, if the sample section of the stored data is different from the corresponding sample section of the search data, the local compare lines coupled to the remaining section of the stored data on each row are latched.

System and method for low power searching in content addressable memories using sampling search words to save power in compare lines

A content addressable memory (CAM) is provided that can perform wide word searches. At least one CAM memory core having a plurality of bit pattern entry rows is included in the CAM. In addition, search logic is included that, is capable searching particular rows during each cycle. The search logic is also capable of allowing match line results of unsearched rows to remain unchanged during a cycle. The CAM further includes a serial AND array in communication with the bit pattern entry rows, wherein the serial AND array is capable of computing a match result for wide word entries that span multiple bit pattern entry rows. In one aspect, a match line enable signal is provided to the serial AND array, which facilitates computation of the match result.

Word search in content addressable memory

Wide word search using serial match line computation in content addressable memory

An invention is provided for low power searching in a CAM using sample words to save power in the compare lines. The invention includes comparing a sample section of stored data to a corresponding sample section of search data on a plurality of rows in the CAM. If a sample section of the stored data on any row of the plurality of rows is equivalent to the corresponding sample section of the search data, a remaining section of search data is allowed to propagate to the local compare lines coupled to the remaining section of the stored data of each row. However, if the sample section of the stored data is different from the corresponding sample section of the search data, the local compare lines coupled to the remaining section of the stored data on each row are latched.

System and method for low power searching in content addressable memories using sample search words to save power in compare lines

An invention is disclosed for reducing power in a CAM using sample words. A sample section of stored data is compared to a corresponding sample section of search data. If the sample section of the stored data is different from the corresponding section of the search data, a non-match result is generated. However, if the sample section of the stored data is equivalent to the corresponding sample section of the search data, the remaining section of the stored data is compared to a corresponding remaining section of the search data. Thus, the remaining section of the stored data is not compared to the corresponding remaining section of the search data if the sample section of the stored data is different from the corresponding section of the search data.

System and method for low power searching in content addressable memories using sample search words

A content addressable memory (CAM) is provided. The CAM includes a search port for performing search operations at each clock cycle and a maintenance port for writing and reading data to address locations of the content addressable memory. An interlock signal is also provided and is communicated from the search port to the maintenance port to establish when writing and reading of data is to be performed to the content addressable memory so that the search operations continue uninterrupted at each clock cycle. Preferably, the interlock signal is communicated at an end of a search operation and at a beginning of a search pre-charge operation. The maintenance port is configured to set-up a writing operation at a beginning of a clock cycle and execute the write operation at the end of the search operation and the beginning of the search pre-charge operation. In another preferred example, search operations can be deselected at any time, yet any desired writing and reading operation can still be executed. At anytime therefore, the search operations can resume operation at each cycle, without being affected by a read or write operation.

Content addressable memory having read/write capabilities that do not interrupt continuous search cycles

Modifications to CAM cell designs are required as supply voltages utilized decrease. In one possible modified design, when a reference bit applied to the CAM cell matches a stored bit, p-channel pass transistors within the CAM cell can pass a full logical high to an n-channel chain transistor coupled within a NAND configuration with other CAM cells. This full logical high can result in increased transition speed, a decrease in degradation, and/or a decrease in power dissipation for the n-channel chain transistor. Further, compared to using n-channel pass transistors, the use of p-channel pass transistors to transfer the logical high voltage can increase the transition speed, decrease the degradation, and/or decrease the power dissipation for the pass transistors. Alternatively, the use of n-channel pass transistors and a p-channel chain transistor can gain similar advantages if the logic was opposite.

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Nepean, Canada

Radu Avramescu