X-Sand Filter: An X-Tolerant Response Compaction Technique for Faster-Than-At-Speed Testing

Faster-than-at-speed testing provides an effective way of detecting small delay defects but at the cost of increased number of unknown logic values on longer paths of the circuit under test. For efficient testing, these unknown logic values need to be filtered out of the circuit under test output. In past, different compaction hardware schemes were presented to minimize these unknown logic values, all these schemes were effective in handling a limited number of unknown values arising due to design imperfections, processing problems manufacturing problems material problems etc. but no effective compaction scheme is available to handle large number of these logic values arising due to faster-than-at-speed testing. This paper presents “X-sand filter”, a compaction technique, an extension of already presented idea of “X-tolerant signature analysis”. Here, the idea of “X-tolerant signature analysis” with modifications has been applied and has attained a considerable improvement in the X-tolerance. X-sand filter is a hierarchical structure that handles gradual X-density reduction in an efficient manner. Simulation results obtained show that we can achieve up to 90 % reduction in the X-density if we use X-sand filter. Extensions to the work of X-sand filter can be carried out in future to enhance its capabilities and make its configuration more flexible in terms of layer designing.