Designing Precharge-Free Energy-Efficient Content-Addressable Memories
Ramiro Taco, Esteban Garzón, Robert Hanhan, Adam Teman, Leonid Yavits, Marco Lanuzza · IEEE Transactions on Very Large Scale Integration (VLSI) Systems · 2024
Content-addressable memory (CAM) is a specialized type of memory that facilitates massively parallel comparison of a search pattern against its entire content. State-of-the-art (SOTA) CAM solutions are either fast but power-hungry (NOR CAM) or slow while consuming less power (nand CAM). These limitations stem from the dynamic precharge operation, leading to excessive power consumption in NOR CAMs and charge-sharing issues in NAND CAMs. In this work, we propose a precharge-free CAM (PCAM) class for energy-efficient applications. By avoiding precharge operation, PCAM consumes less energy than a NAND CAM, while achieving search speed comparable to a NOR CAM. PCAM was designed using a 65-nm CMOS technology and comprehensively evaluated under extensive Monte Carlo (MC) simulations while taking into account layout parasitics. When benchmarked against conventional NAND CAM, PCAM demonstrates improved search run time (reduced by more than 30%) and 15% less search energy. Moreover, PCAM can cut energy consumption by more than 75% when compared to conventional NOR CAM. We further extend our analysis to the application level, functionally evaluating the CAM designs as a fully associative cache using a CPU simulator running various benchmark workloads. This analysis confirms that PCAMs represent an optimal energy-performance design choice for associative memories and their broad spectrum of applications.