High-Throughput Low-Energy Content-Addressable Memory Based on Self-Timed Overlapped Search Mechanism

This paper introduces a self-timed overlapped search mechanism for high-throughput content-addressable memories (CAMs) with low search energy. Most mismatches can be found by searching the first few bits in a search word. Consequently, if a word circuit is divided into two sections that are sequentially searched, most match lines in the second section are unused. As searching the first section is faster than searching an entire word, we could potentially increase throughput by initiating a second-stage search on the unused match lines as soon as a first-stage search is complete. The overlapped search mechanism is realized using a self-timed word circuit that is independently controlled by a locally generated control signal, reducing the power dissipation of global clocking. A 256 x 144-bit CAM is designed under in 90 nm CMOS that operates with 5.57x faster throughput than a synchronous CAM, with 38% energy saving and 8% area overhead.