FREQUENCY SYNTHESIZER

摘要

PURPOSE: A frequency synthesizer is provided to include a VCO(Voltage Controlled Oscillator) having a unit for fine tuning the oscillator frequency and a switchable capacitive element for coarse tuning the oscillator frequency. CONSTITUTION: A frequency synthesizer comprises a voltage controlled oscillator(VCO) having a unit for fine tuning the oscillator frequency and a switchable capacitive element for coarse tuning the oscillator frequency. The first comparison unit compares the frequency and phase of the output of the VCO or a signal derived with that of a reference frequency signal to provide an error signal. The second comparison unit compares the error signal against one or more reference values. A controller receives the result of the comparison from the second comparison unit and switches the switchable capacitive elements on and off in dependence upon the result so as to coarse tune the oscillator frequency.