A Low-Complexity Sensing Scheme for Approximate Matching Content-Addressable Memory

The need for approximate rather than exact search arises in numerous compare-intensive applications, from networking to computational genomics. This brief presents a novel sensing approach for approximate matching content-addressable memory (CAM) designed to handle large Hamming distances (HDs) between the query pattern and stored data. The proposed matchline sensing scheme (MLSS) employs a replica mechanism and a 12-transistor positive feedback sense amplifier to effectively resolve the approximate match operation. The MLSS was integrated into a 4 kB approximate CAM array and fabricated in a 65 nm CMOS technology. With an overall area footprint of 0.0048 mm2, which includes 512 sense amplifiers and the replica mechanism, the MLSS allows a flexible and dynamic adjustment of the HD tolerance threshold via several design variables. Experimental measurements demonstrate the efficiency of our sensing scheme in tolerating very large HDs with the highest sensitivity.