At-speed transition fault testing with low speed scan enable

With today's design size in millions of gates and working frequency in gigahertz range, at-speed test is crucial. The launch-off-shift method has several advantages over the launch-off-capture but imposes strict requirements on transition fault testing due to at-speed scan enable signal. A novel scan-based at-speed test is proposed which generates multiple local fast scan enable signals. The scan enable control information is encapsulated in the test data and transferred during the scan operation. A new scan cell, referred to as last transition generator (LTG), is inserted in the scan chains to generate the fast local scan enable signal. The proposed technique is robust, practice-oriented and suitable for use in an industrial flow.