Input Test Data Volume Reduction Using Seed Complementation and Multiple LFSRs

Test data compression methods reduce the input storage requirements of a test set by storing compressed tests. To enhance the ability to reduce the input test data volume, earlier approaches use the same input test data to apply several different tests. This paper considers two methods that have not been used before for this purpose. The methods are considered in the context where a linear-feedback shift-register (LFSR) is used as part of the decompression logic, and tests are compressed into seeds for the LFSR. The first method complements a bit of a seed to obtain a different test than the one produced by the uncomplemented seed. The second method uses the same seed for different LFSRs to produce different tests. The two methods are used together to demonstrate the advantages of a hybrid approach where the methods complement each other. Experimental results for benchmark circuits are presented to demonstrate the effectiveness of a hybrid approach.