Expedited response compaction for scan power reduction

Transitions embedded in between consecutive stimulus/response bits toggle scan cells during shift operations. The consequent switching activity in the scan chains further propagate into the combinational logic, resulting in elevated power dissipation levels, and thus, endangering the reliability of the chip being tested. Based on the observation that the content of scan chains during shift operations is irrelevant and unimportant, we propose an expedited response compaction technique in order to reduce power dissipation during scan operations. Parallelized (and expedited) compaction operations help compress the entire capture response onto a single reference chain during the first portion of shift cycles, enabling a simultaneous constant-0 feed to all the remaining chains, in which no scan-out power is dissipated during the subsequent shift cycles. This DfT-based approach is nonintrusive for design flow, requires a very minor investment in area, and in turn delivers significant savings in test power. The proposed solution reduces test power without resorting to x-filling, enabling orthogonal x-filling techniques to be applied in conjunction, while retaining the observed responses intact. Experimental results justify the efficacy of the proposed technique in attaining test power reductions.