A Comprehensive Stochastic Design Methodology for Hold-Timing Resiliency in Voltage-Scalable Design

In order to fulfill different demands between ultralow energy consumption and high performance, integrated circuits are being designed to operate across a large range of supply voltages, in which resiliency to timing violation is the key requirement. Unfortunately, traditional timing analysis which focuses on setup timing tolerance for higher performance cannot model the hold violation efficiently across different voltages. In this paper, we proposed a complete flow of computationally efficient methodology for guaranteeing hold margin, which is particularly important for low-power devices, e.g., Internet-of-Things devices. Leveraging both the conventional static timing analysis and a most probable point (MPP) theory, we develop a new hold-timing closure methodology across voltages eliminating expensive Monte Carlo simulation. To improve the efficiency of locating MPP, a novel MPP search method is proposed that employs a set of approximation eliminating the time-consuming iterative search. Several novel modeling techniques, such as the incorporation of nonlinear behaviors of circuit operations and correlation coefficient modeling, are also proposed in this paper to significantly improve the accuracy of the design. With the proposed modeling techniques, a novel hold resilient design technique equipped with the proposed variation-aware timing resilient flip-flop is developed. The proposed design technique eliminates the excessive hold-fixing operation at low voltage and its associated performance degradation at high voltage, whereas still being compatible with the conventional design closure flow. Design example on a voltage-scalable digital signal processor was used to demonstrate the potential of the technique. The result in a 45-nm technology shows that the elimination of more than 20 000 hold buffers, 23% performance improvement at high voltages, and 7% area saving are achieved using the proposed technique compared with the conventional digital design technique.