Synchronization in Quantum-dot Cellular Automata Circuits and Systems

Signal synchronization of large scale Quantum-dot Cellular Automata (QCA) circuits is one of the most complex QCA design challenges. More specifically, the QCA circuits synchronization problem, especially in the large circuits, is characterized as rather complex due to technology constraints. In this paper, by extensively analyzing the most important properties of the signal synchronization problem in QCA circuits, we propose an efficient design methodology to tackle the problem, based on the well-known from computer science, Firing Squad Synchronization Problem (FSSP). Comparing FSSP with the QCA circuits synchronization problem many similarities can be found. Among the numerous FSSP's algorithmic solutions in literature, the Mazoyer algorithm has proven to be the most efficient one. In this paper, a novel design and implementation in QCA technology of this algorithm is presented. Moreover, by the appropriate modification of the Mazoyer algorithm, we are able to propose a generic synchronization design methodology for QCA circuits and systems. This method is enhanced by a novel freezing technique, that makes it applicable to any QCA circuit and system as manifested by our corresponding simulation results. The proposed synchronization methodology is a universal design tool, that can be applied to exiting designs without increasing the complexity.