REBEL and TDC: Two embedded test structures for on-chip measurements of within-die path delay variations

As feature printability becomes more challenging in advanced technology nodes, measuring and characterizing process variation effects on delay and power is becoming increasingly important. In this paper, we present two embedded test structures (ETS) for carrying out path delay measurement in actual product designs. Of the two structures proposed here, one is designed to be incorporated into a customer's scan structures, augmenting selected functional units with the ability to perform accurate path delay measurements. We refer to this ETS as REBEL (regional delay behavior). It is designed to leverage the existing scan chain as a means of reducing area overhead and performance impact. For cases in which very high resolution of delay measurements is required, a second standalone structure is proposed which we refer to as TDC for time-to-digital converter. Beyond characterizing process variations, these ETSs can also be used for design debug, detection of hardware Trojans and small delay defects and as physical unclonable functions.