Statistical timing analysis of flip-flops considering codependent setup and hold times

ABSTRACT

Statistical static timing analysis (SSTA) plays a key role in determining performance of the VLSI circuits implemented in state-of-the-art CMOS technology. A pre-requisite for employing SSTA is the characterization of the setup and hold times of the latches and flip-flops in the cell library. This paper presents a methodology to exploit the statistical codependence of the setup and hold times. The approach comprises of three steps. In the first step, probability mass function (pmf) of codependent setup and hold time (CSHT) contours are approximated with piecewise linear curves by considering the probability density functions of sources of variability. In the second step, pmf of the required setup and hold times for each flip-flop in the design are computed. Finally, these pmf values are used to compute the probability of individual flip-flops in the design passing the timing constraints and to report the overall pass probability of the flip-flops in the design as a histogram. We applied the proposed method to true single phase clocking flip-flops to generate the piecewise linear curves for CSHT. The characterized flip-flops were instantiated in an example design, on which timing verification was successfully performed.

REFERENCES

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INDEX TERMS

Primary Classification:
  B. Hardware
  B.8 Performance and Reliability
      B.8.2 Performance Analysis and Design Aids

General Terms:
Algorithms, Design, Performance, Reliability

Keywords:
codependency, hold time, piecewise linear, probability, process variations, setup time, statistical static timing analysis (SSTA)