IEEE Access (Jan 2024)
Weak and Strong Non-Robust Tests for Functionally Possible Path Delay Faults
Abstract
Small delay defects are caused by fabrication imperfections as well as chip aging, and detected by tests for path delay faults. Path delay faults that can cause failures during functional operation are especially important to detect. Such path delay faults are referred to as functionally possible or FPPDFs, and are the subject of this article. FPPDFs are identified by generating tests referred to as functional launch-on-capture (FLOC) tests. The propagation conditions used when generating tests for path delay faults determine the ability of off-path delays to invalidate a test. The propagation conditions can be robust, strong non-robust or weak non-robust. An FPPDF with a weak non-robust FLOC test can cause failures during functional operation. However, a weak non-robust test is also the most likely to be invalidated by off-path delays. Therefore, for fault detection, strong non-robust tests are preferred. In addition, conventional launch-on-capture (LOC) or launch-on-shift (LOS) tests are preferred since they are amenable to the conventional test compaction and test data compression approaches that are not applicable to FLOC tests. The contributions of this article are a study of the roles of weak and strong non-robust FLOC, LOC and LOS tests in the detection of FPPDFs, and a metric for predicting whether strong non-robust LOC and LOS tests are likely to exist for a significant number of FPPDFs. A test generation procedure is implemented in an academic environment and applied to benchmark circuits to demonstrate the roles of the various propagation conditions and tests, and the ability to predict the need to generate strong non-robust LOC and LOS tests.
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