Negative-skewed shadow registers for at-speed delay variation characterization

The increased process, voltage, and temperature (PVT) variability that comes with integrated circuit (IC) technology scaling has become a major problem in the semiconductor industry. In order to refine manufacturing processes and develop circuit design techniques to cope with variability, we must be able to accurately and precisely characterize the variations that occur. In this paper, we introduce a technique for characterizing combinational path delay variations by measuring a designer-controlled number of register-to-register delays in manufactured ICs with negative-skewed shadow registers. This technique enables delay measurements to be performed with at-speed tests that are run in parallel with and are orthogonal to other testing techniques, and therefore does not add combinatorial complexity to the testing process. This technique can be implemented cost-effectively on a large number of otherwise unobservable internal combinational paths to get accurate, precise data about delay variability.