Phase-locked loop with automatic frequency tuning

摘要

A PLL frequency synthesizer able to automatically set an appropriate operating mode of the voltage controlled oscillator is provided. The voltage controlled oscillator is operable in a plurality of operating modes each defining a different operating frequency range of the voltage controlled oscillator. The appropriate operating mode is selected based on an error signal detected by a phase/frequency detector of the PLL frequency synthesizer. A window comparator is used for switching to adjacent operating modes if the error signal exceeds or falls below predefined upper and lower error voltage limits.