Frequency Synthesizer

摘要

A frequency synthesiser comprises a voltage controlled oscillator, VCO, 1 having means for fine tuning the oscillator frequency and switchable capacitive elements for coarse tuning the oscillator frequency. First comparison means 3 are provided for comparing the frequency and phase of the output of the VCO 1 or a signal derived therefrom with that of a reference frequency signal to provide an error signal, the error signal being provided to said means for fine tuning the oscillator frequency. Second comparison means 6a,6b are provided for comparing the error signal against one or more reference values and a control means 2 receives the result of the comparison from the second comparison means and switches said switchable capacitive elements on and off in dependence upon the result so as to coarse tune the oscillator frequency. <IMAGE>