Frequency synthesizer using intermittently controlled phase locked loop

Claim 1

A frequency synthesizer, comprising: a reference signal oscillation unit for providing a reference signal; a phase locked loop comprising a voltage controlled oscillator for generating a carrier frequency dependent on a control voltage applied thereto, a frequency division circuit for dividing said carrier frequency to provide a divided frequency by a predetermined division ratio, a phase comparator for comparing said reference frequency and said divided frequency to provide a phase difference, a charge pump for applying a charging voltage and a discharging voltage to a nodal point, a loop filter having a capacitor connected to said nodal point for generating said control voltage to be applied to said voltage controlled oscillator, and a loop on/off switch for closing and opening said phase locked loop; a control unit comprising a power supply control circuit for applying an operative voltage to said phase locked loop which is closed by said loop on/off switch which is turned on intermittently for a switch-over of channels, an open loop control circuit for controlling said loop on/off switch to be turned on and off in accordance with intermittent operation of said phase locked loop, and a selectively operable voltage control circuit for controlling an application of a coarsely controlled voltage to said voltage controlled oscillator for said switch-over of channels in a communication frame, said coarsely controlled voltage being proportional to a difference between frequencies of channels for said switch-over; and a control voltage coarse adjustment circuit for generating said coarsely controlled voltage to be added to said control voltage of said capacitor in said loop filter by a control of said voltage control circuit.