Analysis of oscillatory metastable operation of an RS flip-flop

With continuing advances in VLSI technology, there is a growing interest in large-scale parallel systems with numerous high-frequency asynchronous interactions. However, these interactions may result in frequent failures due to metastable operation of flip-flops used as synchronizers or arbiters. For some flip-flops the metastable operation may be of an oscillatory nature, before finally resolving one of the stable states. An analysis of this mode of metastable operation based on a modified dynamic RS flip-flop model is presented. Analytical formulas for the frequency of the oscillatory metastable operation are derived. Good agreement is observed between the theoretical results, SPICE simulation, and experiments with two CMOS RS flip-flops. Failure rate due to oscillatory metastable operation is discussed based on the experimental results.>