A 128-kbit Approximate Search-Capable Content-Addressable Memory (CAM) with Tunable Hamming Distance

The growing need for approximate matching in data-intensive applications, such as data analytics, machine learning, deep learning, and computational genomics has driven the proposal of our Hamming distance (HD) tolerant content-addressable memory (HD-CAM). HD-CAM features a modified nor-type associative memory cell that leverages the discharge speed of the matchline (ML) to directly measure the HD between the stored and the query patterns. This novel approach enables efficient in-memory approximate matching. The proposed design was fabricated in a 65-nm technology, running at 125 MHz with an operating voltage of 1.2 V and consuming approximately 0.2 fJ/bit/search at room temperature. HD-CAM features a user-programmable HD tolerance threshold, making it particularly efficient for compare-intensive applications, such as genome analysis, text processing, and database processing. Silicon measurements demonstrate that HD-CAM maintains F₁ score above 90% under process, voltage, and temperature (PVT) variations across a range of HDs.