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Current memory testing methods rely on fault models that are inadequate to accurately represent potential defects that occur in modern, often specialized, memories. To remedy this, the authors present a formal framework for modeling and testing special-purpose memories. Their approach uses three models: the transistor circuit, the event-sequence model, and finite-state machines. The methodology is explained using the example of a content-addressable memory (CAM). The fault model they describe comprises input stuck-at, transistor, and bridging faults. The authors show that functional tests can reliably detect all input stuck-at faults, most transistor faults (including all stuck-open faults), and about 50% of bridging faults. The remaining faults are detectable by parametric tests. A test of length 7n+2l+9 that detects all the reliably testable faults in an n-word by l-bit CAM is presented. A CAM test by Giles & Hunter is evaluated with respect to the input stuck-at faults. It is shown that this test fails to detect certain faults; it can be modified to achieve full coverage at the cost of increased length.
Computer-Aided Design of Integrated Circuits and Systems, IEEE Transactions on (Volume:21 , Issue: 12 )
Date of Publication: Dec 2002