Output gating performance overhead elimination for scan test

Abstract

Switching activity is much higher in test mode as compared to normal mode of operation which causes higher power dissipation, and this leads to several reliability issues. Output gating is proposed as a very effective low-power test technique, which is used to eliminate redundant switching activity in the combinational logic of circuit under test (CUT) during the shifting of test vectors in a scan chain. This method reduces the average power significantly, but it introduces performance overhead in normal mode of operation. In this work, a new output gating technique is proposed which eliminates redundant switching activity in combinational logic of CUT during shifting of test vectors without any negative impact on performance as compared to earlier proposed output gating techniques. The proposed design also improves the performance of the scan flop in functional mode with negligible area overhead incurred due to extra transistors. Experimental results show that our design has a more robust performance over wide range of capacitive load as compared to earlier designs.