Synthesis of Zero-Aliasing Elementary-Tree Space Compactors

A new method is presented for designing space compactors for either deterministic testing or pseudorandom testing. A tree of elementary gates (AND, OR, NAND, NOR) is used to combine the outputs of the circuit-under-test (CUT) in a way that zero-aliasing is guaranteed with no modification of the CUT. The elementary-tree is synthesized by adding one gate at a time without introducing redundancy. The end result is a cascaded network, CUT followed by space compactor, that is irredundant and has fewer outputs than the CUT alone. All faults in the CUT and space compactor can be tested. Only the outputs of the space compactor need to be observed during testing. Experimental results are surprising; they show that very high compaction ratios can be achieved with zero-aliasing elementary-tree space compactors. Compared with parity trees and other space compactor designs that have been proposed, the method presented here requires less overhead and yet guarantees zero-aliasing.