Redundancy and testability in digital filter datapaths

Test issues in application-specific digital filter datapaths are investigated. It is found that such designs can contain hundreds of redundant faults, making it difficult to accurately determine fault coverage. Since these redundant faults tend to appear in the same general location as test-resistant faults, the presence of many redundant faults can hide significant untested faults despite high overall test coverage. Classes of redundant faults that arise in digital filter datapaths are described, and we propose a suite of techniques for identifying and eliminating the most common redundancies based on arithmetic optimization. The approach is suitable as a front-end to more accurate fault simulation, or can be used in the design process to eliminate redundant logic. The approach is validated as a tool for developing very high-coverage built-in self-test circuits, showing that 100% fault coverage can be achieved in 24k-gate filters with as little as 1% area overhead. When used as a datapath optimization technique, the average area reduction over 15 designs was 8.9%, compared with moderately optimized designs. As a front-end to fault simulation, the approach yielded a 97.9% average reduction in the number of undetected faults across the 15 designs.