Testing and Diagnosing Comparison Faults of TCAMs with Asymmetric Cells

Ternary content addressable memory (TCAM) is a key component in various digital systems due to its fast lookup operation. Symmetric and asymmetric TCAM cells are two widely used cells for implementing a TCAM array. This paper presents several comparison fault models of TCAMs with asymmetric cells based on electrical defects. Some new comparison faults which do not exist in a TCAM with symmetric cells are found. One march-like test algorithm T_AC-H is also proposed to cover the defined comparison faults. The T_AC-H consists of 8N Write operations and (3N + 2B) Compare operations for an N × B-bit TCAM with Hit output only. We also propose two march-like diagnosis algorithms to identify the defined comparison faults of TCAMs with asymmetric cells. The first diagnosis algorithm D_AC-H requires 5N Write operations, 3N Erase operations, and (5N + 2B) Compare operations to distinguish 100 percent comparison faults for a TCAM with Hit output only. The second diagnosis algorithm D_AC-P requires 3N Write operations, 1N Erase operations, and (5N + 2B) Compare operations to distinguish 100 percent comparison faults for a TCAM with Hit and priority address encoder outputs.