Feedback based droop mitigation

A strong dl/dt event in a VLSI circuit can induce a temporary voltage drop and consequent malfunctioning of logic as for instance failing speed paths. This event, called power droop, usually manifests itself in at-speed scan test where a surge in switching activity (capture phase) follows a period of quiescent circuit state (shift phase). Power droop is also present during mission mode operation. However, because of the less predictable occurrence of the switching events in mission mode, usually the values of power droop measured during test are different from those measured in mission mode. To overcome the power droop problem, different mitigation techniques have been proposed. The goal of these techniques is to create a uniform current demand throughout the test. This paper proposes a feedback based droop mitigation technique which can adapt to the droop by reading the level of VDD and modifying real time the current flowing on ad-hoc droop mitigators. It is shown that the proposed solution not only can compensate for droop events occurring during test mode but also can be used as a method of mission mode droop mitigation and yield enhancement if higher power consumption is acceptable.