A simple and practical synchronization system with the memory function

This article describes a simple and practical synchronization system which mainly applied in power managements. The system provides three features: First, the circuit can work at its own internal oscillation frequency when without a synchronous signal. Second, when adding an external signal, the system will take advantage of digital technology to synchronize the external frequency and output it. Third, during the synchronous process, the system will remember the applied frequency value, and keep working at a value which is equal to the originally synchronous frequency after the external signal is disconnected with the circuit suddenly. Although there is a tiny error between these two frequencies which is smaller than 5 percentages, the error can be reduce perpetually. This system can be synchronized between 350KHZ to 770KHZ. Simulation results using a 0.5μm BCD process are presented and discussed.