Frequency synthesizer having phase-locked loop including sample and hold circuit frequency converter

Claim 1

A circuit arrangement for generating a plurality of spaced channel frequencies lying within at least one frequency range comprising: a first voltage controlled oscillator; a frequency converter coupled to the output of said first voltage controlled oscillator; an adjustable frequency divider coupled to the output of said frequency converter; said adjustable frequency divider being also a channel selector; a crystal oscillator; a fixed frequency divider coupled to the output of said crystal oscillator, the output frequency of said fixed frequency divider being a reference frequency having a value equal to the channel spacing; a phase comparator coupled to said adjustable frequency divider and said fixed frequency divider to provide a control signal proportional to the frequency difference between the output frequencies of said adjustable frequency divider and said fixed frequency divider; and a first low pass filter to couple said control signal from said phase comparator to said first voltage controlled oscillator for frequency control thereof; said frequency converter including a sample and hold circuit coupled to the output of said first voltage controlled oscillator, a pulse generator coupled to said crystal oscillator to produce a sampling pulse for application to said sample and hold circuit to sample the output frequency of said first voltage controlled oscillator, and a low pass filter coupled to the output of said sAmple and hold circuit to couple the converted frequency to said adjustable frequency divider, said sampling pulse having a pulse width which is very small as compared to the period of the output frequency of said first voltage controlled oscillator.