A precharge free dynamic content addressable memory (DCAM) is introduced for low-power and high-speed search applications. Elimination of precharge prior to search allows hardware engine to perform more number of searches within the stipulated time. The proposed DCAM cell not only removes precharge of matchline (ML) but also utilises decoupling of bitline and searchline so that unwanted capacitive couplings are minimised at charge storage nodes. A 512 bit of the proposed scheme is implemented using 45 nm CMOS technology and its efficacy is verified and proved through rigorous variations with 1000-point Monte-Carlo sampling of ML voltage as well as multi-search dissipation analysis.
Performance of a memory depends on the storage stability, yield and sensing speed. Differential input and the latching time of sense amplifiers are considered as primary performance factors in static random access memory. In a content addressable memory (CAM), the sensing is carried out through the matchline (ML) and the time for evaluation is the key to decide the search speed. The density of CAM is on a rise to accommodate a higher amount of information which increases the power dissipation associated with it. Issues such as the logical threshold variation and lower noise margin between match and mismatch are critical in the operation of a CAM. A good ML sensing technique can reduce the ML power with enhanced evaluation speed. This work provides an analogy of various ML sensing techniques based on their pre-charging, evaluation and performance improvement strategies. Estimation on the power dissipation and evaluation time are made and in-depth analysis on their power-speed-overhead trade-off are carried on 64-bit CAM macros.
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