Analysis of Path Delay Fault Testability for Two-Rail Logic Circuits

Kazuteru NAMBA  Hideo ITO  

IEICE TRANSACTIONS on Fundamentals of Electronics, Communications and Computer Sciences   Vol.E92-A   No.9   pp.2295-2303
Publication Date: 2009/09/01
Online ISSN: 1745-1337
DOI: 10.1587/transfun.E92.A.2295
Print ISSN: 0916-8508
Type of Manuscript: PAPER
Category: VLSI Design Technology and CAD
two-rail logic circuit,  path delay fault,  testability,  functional sensitizability,  over-testing,  

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The importance of redundant technologies for improving dependability and delay fault testability are growing. This paper presents properties of a class of redundant technologies, namely two-rail logic, and analyzes testability of path delay faults occurring on two-rail logic circuits. The paper reveals the following characteristics of two-rail logic circuits: While the number of paths in two-rail logic circuits is twice that in ordinary single-rail logic circuits, the number of robust testable path delay faults in two-rail logic circuits is twice or more that in the single-rail logic circuits. This suggests two-rail logic circuits are more testable than ordinary single-rail logic circuits. On two-rail logic circuits, there may be some robust testable path delay faults that are functional un-sensitizable for any input vectors consisting of codewords of two-rail codes, i.e. for any input vectors that can occur during fault-free operation. Even if such faults occur, the circuits are still strongly fault secure for unidirectional stuck-at faults as well as they work correctly.