Bit-Complemented Test Data to Replace the Tail of a Fault Coverage Curve

The fabrication processes of chips in state-of-the-art technologies may introduce defects of various types, and a large number of tests may be needed for fault detection. However, constraints on the storage requirements of a test set can limit the number of tests and, consequently, the fault coverage. It was shown earlier that reductions in the input storage requirements of a test set can be achieved by using the same stored tests for applying several different tests. One of the operators used for this purpose complements bits of applied tests. The key contributions of this article to this scenario are the following. These issues are considered here for the first time: 1) the use of bit-complemented tests is guided by the fault coverage curve of a complete test set and bit-complementation is applied to tests from the beginning of the fault coverage curve to replace tests at the tail of the curve that detect small numbers of faults; 2) the input and output test data volume are considered together and bit-complementation is used for storing both the tests and their output responses; and 3) the procedure described in this article explores the tradeoff between the storage requirements and the number of applied tests. Experimental results for single-cycle gate-exhaustive faults in benchmark circuits demonstrate the tradeoff.