Content addressable memory having dynamic match resolution
View Patent ↗A content addressable memory (CAM) architecture. For one embodiment, the CAM architecture includes a plurality of rows of CAM cells, each row configured to generate match results on a corresponding match line, a number of comparand lines, each coupled to a corresponding CAM cell in each of the plurality of rows of CAM cells, a plurality of timed storage circuits, each having a data input coupled to a corresponding match line and having an enable input coupled to an enable signal line, a timing generator configured to generate an enable signal on the enable signal line, and a plurality of load elements.
1. A content addressable memory (CAM) device comprising:
a plurality of rows of CAM cells, each row configured to generate match results on a corresponding match line;
a plurality of comparand lines each coupled to a corresponding CAM cell in each of the plurality of rows of CAM cells;
a plurality of timed storage circuits each having a data input coupled to a corresponding match line and an enable input; and
an enable signal line extending substantially parallel to the comparand lines and coupled to the enable input of each of the timed storage circuits, the enable signal line being coupled to a plurality of load elements such that a signal propagating on the enable signal line propagates in substantially the same direction and at substantially the same rate as signals propagating on the comparand lines.
2. The CAM device of claim 1 further comprising a timing generator to output an enable signal to the plurality of timed storage circuits via the enable signal line.
3. The CAM device of claim 1 wherein the number of load elements is substantially equal to the number of rows of CAM cells.
4. The CAM device of claim 1 wherein the number of load elements is fewer than the number of rows of CAM cells.
5. The CAM device of claim 1 wherein the plurality of load elements comprises a column of CAM cells that does not affect the match results generated by the plurality of rows of CAM cells.
6. A method of operation within a content addressable memory device, the method comprising:
outputting comparand data to a plurality of rows of CAM cells via a plurality of comparand lines;
comparing the comparand data with data stored in the plurality of rows of the CAM cells and generating match results on a plurality of match lines;
outputting a first signal onto a signal line that is disposed substantially parallel to the comparand lines and loaded by a plurality of load elements such that the first signal propagates in substantially the same direction and at substantially the same rate as the comparand data propagating on the plurality of comparand lines; and
capturing the match results in response to the first signal.
7. The method of claim 6 wherein outputting the enable signal onto the enable signal line comprises outputting the enable signal onto the enable signal line after a time delay that approximates a time required to generate a match result within one of the rows of CAM cells.
8. The method of claim 6 wherein capturing the match results in response to the first signal comprises storing the match results in a plurality of storage circuits in response to the first signal.
9. The method of claim 6 wherein capturing the match results in response to the first signal comprises:
receiving the first signal in a timing generator;
outputting an enable signal from the timing generator in response to the first signal; and
capturing the match results in a plurality of storage circuits in response to the enable signal.
10. The method of claim 9 wherein outputting the enable signal from the timing generator in response to the first signal comprises outputting the enable signal after a time delay that approximates a time required to generate a match result within one of the rows of CAM cells.
11. The method of claim 10 wherein outputting the enable signal after a time delay that approximates a time required to generate a match result within one of the rows of CAM cells comprises dynamically determining the time delay.
12. The method of claim 11 wherein dynamically determining the time delay comprises performing a compare operation in a row of CAM cells that does not generate a match result on the plurality of match lines.
13. The method of claim 6 wherein outputting the first signal onto the signal line comprises outputting the first signal onto a comparand line that is coupled to a column of CAM cells.
14. The method of claim 13 wherein the column of CAM cells does not affect the match results generated on the plurality of match lines.