Analysis and design of optimal combinational compactors [logic test]

Scan and logic built-in self-test (BIST) are increasingly used to reduce test cost. In these test architectures, many internal signals are observed through a small number of output pins or into a small signature analyzer, requiring a combinational space compactor. This paper analyzes the basic requirements of compactors to support efficient test and diagnosis, focusing on practical compactors where all inputs have a fanout of two. We show how graph theory can be used to model compactors and design compactors with robust non-aliasing properties that have minimal area and delay overhead and are independent of the test set, the fault model, and the circuit tested.