Analysis of adaptive threshold modulation used in pulse stuffing and pointer adjustment schemes

Pulse stuffing and pointer adjustment are necessary for clock rate adaptation in synchronizers used in synchronous digital transmission networks (e.g.,, SDH/SONET). The method of adaptive threshold modulation (AT-Mod) may be used in the synchronizer to reduce the resulting waiting time jitter. This paper in detail addresses the performance of the method of AT-Mod technique. Using a nonlinear model to represent the thresholder, the paper provides mathematical expressions for the filtered jitter power resulting from AT-Mod in the synchronizer. The accuracy of using such a nonlinear technique is also demonstrated. Furthermore, the possibility of improving the AT-Mod circuit for further jitter reduction is discussed. Because the improved AT-Mod circuits are not always guaranteed to be stable, a stability analysis is presented. The impact of input noise on the filtered jitter is also investigated in the paper.