Reducing Power Dissipation during Test Using Scan Chain Disable

A novel approach for minimizing power during scan testing is presented. The idea is that given a full scan module or core that has multiple scan chains, the test set is generated and ordered in such a way that some of the scan chains can have their clock disabled for portions of the test set. Disabling the clock prevents flip-flops from transitioning, and hence reduces switching activity in the circuit. Moreover, disabling the clock also reduces power dissipation in the clock tree which often is a major source of power. The only hardware modifcation that is required to implement this approach is to add the capability for the tester to gate the clock for one subset of the scan chains in the core. A procedure for generating and ordering the test set to maximize the use of scan disable is described. Experimental results are shown indicating that the proposed approach can significantly reduce both logic and clock power during testing.