Test and Diagnosis for Small-Delay Defects

h IN THE GOOD old days we worried about testing stuck-at faults, which had the virtues of being simple, static, and testable with one pattern. Then, we found that detecting all these faults still left some defects untested, so we added transition and path delay faults. These required a two-pattern test, but were still static. Once you detected all of them, you knew your test was of high quality. However, we learned that delay faults, which involve circuit timing, are not static. The amount of time it takes a signal to rise or fall depends on its environment. If neighboring signals switch in the opposite direction, rise or fall times might increase, and if the neighboring signals are changing in the same direction, they might decrease. If a lot of nearby signals change, noise on the power supply is induced and delays may increase. So, things are not as simple as we thought. Test and Diagnosis for Small-Delay Defects addresses these problems. Small delay defects (SDDs) are those of magnitude small enough that they cause failures only if on long paths. They are of interest because many test generation methods find relatively short paths on which to propagate the effects of delay faults. This means some SDDs may not be detected, which can lead to failures when the design is operating at full speed and the long paths are sensitized. The reader should be aware that this book is not a tutorial on SDDs, but rather a collection of new testing methods, which build in each chapter. However, the book does not describe a way of generating patterns to detect SDDs, but rather is an example of a new trend in testing, the development of methods to select patterns from a larger set. The precursor of this method is the use of fault simulation to determine which of a large number of randomly generated scan patterns detect faults, which are then used as a prelude to traditional test generation. Recent work at the University of California Santa Barbara selects effective functional patterns from patterns developed for verification, and adaptive testing can be seen as a way of selecting the best tests for the current state of a manufacturing process from a larger set. In all these cases, you need a relatively simple or preexisting set of patterns to select from. In this book, this role is filled by using n-detect transition patterns, which, if n is large enough, are effective if inefficient. Much of the book builds on this concept, introducing new methods of selection for the conditions which might cause timing failures. As I mentioned, this is not a book for those new to the field. However, it appears that publishers require an introduction to testing in each test book. This requirement is filled by the first chapter, which introduces the entire field in only 18 diagram filled pages, andwhich is a model of conciseness and lucidity and should be an example for all writers of these books. Chapter 2 is an introduction to delay test, SDDs, and briefly summarized the state of the field. Reviewed in this issue Test and Diagnosis for Small-Delay Defects, by Mohammad Tehranipoor, KePeng, andKrishnenduChakrabarty. (Springer, 2011, ISBN 978-1-44198296-4, 228 pp.).