Content-addressable memory with soft-match capability

Details Content-addressable memory with soft-match capability Content-addressable memory with soft-match capability

1989-10-06

1991-10-01

Popek, Joseph A.

Static information storage and retrieval

Associative memories

Ferroelectric cell

364200, 3642531, 3642592, G11C 1500

Patent

active

050539914

ABSTRACT:
Each word location (18-0, 18-1, 18-255) in a content-addressable memory has a tally circuit (24-0, 24-1, 24-255) associated with it. A data word on data lines (12) is compared simultaneously with the words in all of the word locations, and the tally circuit associated with each location counts the number of matches between the key word in that location and the data word represented by the signals on the data line. The tally circuits apply tally signals representing the number of matching bits in their respective word locations to comparison circuits (28-1, 28-255), each of which compares the tally output from its associated tally circuit with the output from a previous comparison circuit and forwards the higher of the two to the next comparison circuit. Each comparison circuit also applies to a priority encoder (32) an output that indicates whether the associated tally circuit has generated a tally signal representing a tally greater than that from all previious locations. The encoder circuit (32) encodes the address of the location having the highest tally, and the output of the last comparison represents the highest tally is. In this manner, the content-addressable memory (10) can be addressed by the closest match, not only by an exact match.

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Wade, J. P. and C. G. Sodini, "Dynamic Cross-Coupled Bitline Content Addressable Memory Cell for High Density Arrays", IEEE International Electron Devices Meeting, 1985.

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