Noise Modeling Effects in Redundant Synchronizers

The effects of redundancy and masking on the reliability of synchronizer circuits in the presence of metastability are considered. It is shown that in the jitter model developed by L. Kleeman (1990), in which circuit noise effects are considered, redundancy improves the probability of metastable failure of synchronizers, contrary to Kleeman's claim. A stochastic model that relates the noise model to the absorbing barrier problem for such noise effects is presented. It is demonstrated analytically that under considerably general conditions on the (masking) (Bcombinational circuit, clock delay, voter delay, and aperture alignment and width, the probability of metastable failure of the redundant synchronizer tends to zero with L, the number of component synchronizers. If the component synchronizers are identical, this probability of metastable failure decreases monotonically with L. Furthermore, the best combinational circuits to use in the general redundant synchronizer are the L-input AND and OR functions. Conditions are derived under which the majority voter function may or may not be effective in a general redundant synchronizer. >