X-Tolerant Compactor with On-Chip Registration and Signature-Based Diagnosis

This article describes a two-stage test response compactor with an overdrive section, scan chain selection logic, and an on-chip comparator and registration scheme for efficient signature-based diagnosis. This solution offers compaction ratios much higher than those determined by the ratio of scan chains to compactor outputs, and it guarantees very good observability and diagnostic resolution of scan errors, even for a large number of Xs. Experimental results confirm that the proposed solution does not compromise test quality and requires a minimal amount of information to control the compactor itself.