Feedback-bus oscillation ring: A general architecture for delay characterization and test of interconnects

In this paper we propose a flexible delay characterization and test architecture, called Feedback-Bus Oscillation Ring (FB-OR), for die-to-die interconnects in a 3D IC. As compared to previous works, it is unique in its ability to streamline the characterization/test operations for a set of arbitrary interconnects with multiple pins sprawling multiple dies. During the Design-for-Testability stage, one common feedback-bus (connected to all dies in the IC under characterization/test) is inserted. Through this feedback-bus, an oscillation ring can be formed dynamically and the Variable-Output-Threshold (VOT) technique can be applied to characterize the delay of one interconnect segment at a time. Experimental results indicate that this method is not only flexible and scalable, but requiring only a small area overhead.