On compacting test response data containing unknown values

The design of a test response compactor called a Block Compactor is given. Block Compactors belong to a new class of compactors called Finite Memory Compactors. Different from space compactors, finite memory compactors contain memory elements. Also unlike time compactors, finite memory compactors have finite impulse response. These properties give finite memory compactors the ability to achieve higher compaction ratios than space compactors and still be able to tolerate unknown values in test responses. The proposed Block Compactors, as an instance of finite memory compactors generate a signature of response data in several scan cycles. Results presented on several industrial designs show that Block Compactors provide better test quality and higher data compaction than earlier works on test response compactors.