Soft-error protection of TCAMs based on ECCs and asymmetric SRAM cells

Content-addressable memories (CAMs) enable the comparison of their entire content to a search word in one single access. Ternary CAMs (TCAMs) provide the possibility to store and handle not only 0 s and 1 s but also don´t cares. A way to protect TCAMs implemented with static random-access memory (SRAM) cells against soft-errors is proposed. Asymmetric SRAM cells are used to reduce the probability that soft-errors (a) affect don´t cares and (b) corrupt 0 s and 1 s into anything else than a don´t care. This implies that soft-errors will only have the tendency to generate false-hits that point to an erroneous matching word. Such a failure can be mitigated with the help of an error-correcting code (ECC), as is the case with conventional memories. Other types of failures which are more difficult to detect and locate, i.e. false-misses or false-hits that point to an error-free matching word or false-misses, become very rare or non-existent.