Scan Shift Power Reduction by Freezing Power Sensitive Scan Cells

In this paper, we show that not every scan cell contributes equally to the power consumption during scan-based test. The transitions at some scan cells cause more toggles at the internal signal lines of a circuit than the transitions at other scan cells. Hence the transitions at these scan cells have a larger impact on the power consumption during test application. We call these scan cells power sensitive scan cells. A signal probability based approach is proposed to identify a set of power sensitive scan cells. Additional hardware is added to freeze the outputs of power sensitive scan cells during scan shifting in order to reduce the shift power consumption. Experimental results on industrial circuits show that on average more than 45% of the scan shift power can be eliminated when freezing only 5% of power sensitive scan cells.