Testing of critical paths for delay faults

Testing the critical paths in a circuit is essential to cover distributed delay and small delay defects in a manufactured circuit. However, in most circuits, only a small percentage of functionally irredundant critical paths (which can affect the cycle time) are robustly testable. We propose the covering of defects on untestable critical paths by robustly testing the longest testable segments lying on those paths. This method is scalable to large circuits since the task of segment delay fault test generation has complexity similar to path delay fault test generation. Experimental results have been given to demonstrate that significant additional coverage of defects on critical paths can be achieved using this technique.