Explaining Metastability in Real Synchronizers

In 2007, Yang and Greenstreet presented an algorithm that enables the computation of synchronizer failure probabilities, even when these probabilities are extremely small. Their approach gives a single probability number for the synchronizer but does not explain how the circuit details within the synchronizer contribute to the final result. We present an extension of their algorithm that connects the time-to-voltage gain of a synchronizer to the propagation of metastability through the circuit. This allows the designer to see what circuit features are helpful or not for synchronizer performance. There exists abundant folklore about what helps or hinders multistage synchronizer performance. We use our analysis to examine and explain two examples of such synchronizer folklore.