Frequency synthesizer

Claim 1

A frequency synthesizer for use in a multichannel radio apparatus, said frequency synthesizer having a first oscillator for outputting a signal having a reference frequency, a first frequency divider for dividing the frequency of the signal outputted from said first oscillator, a second oscillator for outputting a signal having a desired frequency, a second frequency divider for dividing the frequency of the signal outputted by said second oscillator by a variable number, a phase comparator for comparing the phase of the signal outputted from said first frequency divider with that of the signal outputted from said second frequency divider, a charge pump for converting an output signal of said phase comparator and outputting the converted signal as an integrator drive signal and an integrator for integrating the output signal of said charge pump and controlling said second oscillator, the improvement comprising: a first gate circuit provided between said first oscillator and said first frequency divider; a second gate circuit provided between said second oscillator and said second frequency divider; a third gate circuit between said charge pump and said integrator; a control circuit responsive to an output signal from said first or second frequency divider, a frequency synthesizer controlling signal, and output signals from said phase comparator for producing first and second gate control signals respectively applied to said first and second gate circuits; and a frequency division ratio setting circuit having a shift register, an N-bit data latch responsive to parallel outputs from said shift register, and means for controlling said data latch by logical product of a first signal inputted from a strobe input terminal and a second signal outputted from another data latch which holds a first or last one bit of said parallel outputs of said shift register thereby controlling frequency division ratio of said first and second frequency dividers by outputs of said N-bit data latch.