Testing and Diagnosis Methodologies for Embedded Content Addressable Memories

Embedded content addressable memories (CAMs) are important components in many system chips where most CAMs are customized and have wide words. This poses challenges on testing and diagnosis. In this paper two efficient March-like test algorithms are proposed first. In addition to typical RAM faults, they also cover CAM-specific comparison faults. The first algorithm requires 9N Read/Write operations and 2(N + W) Compare operations to cover comparison and RAM faults (but does not fully cover the intra-word coupling faults), for an N × W-bit CAM. The second algorithm uses 3N log2W Write and 2W log2W Compare operations to cover the remaining intra-word coupling faults. Compared with the previous algorithms, the proposed algorithms have higher fault coverage and lower time complexity. Moreover, it can test the CAM even when its comparison result is observed only by the Hit output or the priority encoder output. We also present the algorithms that can locate the cells with comparison faults. Finally, a CAM BIST design is briefly described.