Testing Ternary Content Addressable Memories With Comparison Faults Using March-Like Tests

Ternary content addressable memory (TCAM) plays an important role in various applications for its fast lookup operation. This paper proposes several comparison fault models (i.e., the faults cause Compare operation fail) of TCAMs based on electrical defects, such as shorts between two circuit nodes and transistor stuck-open and stuck-on faults. Two March-like tests for detecting comparison faults are also proposed. The first March-like test requires 4N Write operations, 3N Erase operations, and 4N+2B Compare operations to cover 100% of targeted comparison faults for an NtimesB-bit TCAM with Hit output only. The second March-like test requires 2N Write operations, 2N Erase operations, and 4N+2B Compare operations to cover 100% of targeted comparison faults for an NtimesB-bit TCAM with Hit and Priority Address Encoder outputs. Compared with the previous work, the proposed tests have lower time complexity for typical TCAMs; they can be used to test TCAMs with different comparator structures; and their time complexities are independent of the number of stuck-on faults. Also, they can cover delay faults in comparison circuits

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