Phase shifts and linear dependencies

Two-dimensional scan design is a widely used BIST architecture for pseudo-random and pseudo-exhaustive testing. However, linear dependencies that arise due to the properties of the test-pattern generators in use have a negative impact on fault coverage. To alleviate this problem, networks of XOR gates known as phase shifters are often used. Existing techniques for selecting phase shifts, such as those based on large channel separations, lead to inadequate removal of linear dependencies. In this paper we present for the first time a method for the selection of appropriate channel phase shifts to explicitly minimize linear dependencies. Experimental results corroborate the effect of the approach in increasing fault coverage