Two-Gear Low-Power Scan Test

We introduce in this paper a new scan test methodology that can be programmed to execute in one of two gears - that is, the low-shifting-power scan, and the low-capture-power scan, in one single scan-architecture. This two-gear method provides layered treatment to potential power-induced test failure. First, it attempts to perform scan test in gear 1 without any test time overhead over the traditional scan. Second, in case the failure is caused by excessive capture power, then the test yield loss could be recovered by switching the operation to gear 2, which is a low-capture-power mode, at the cost of extra test time. This methodology is fully compatible with existing DFT tool and requires only small area overhead.