PLL having two-frequency VCO

Claim 1

A periodic signal generator synchronized to an incoming signal whose amplitude continuously varies at a frequency fi comprising: a signal controlled oscillator means for generating either a first signal periodically varying at a first frequency greater than but in the neighborhood of four times the frequency fi in response to the receipt of a first value of a binary signal or a second signal periodically varying at a second frequency less than but in the neighborhood of four times the frequency fi in response to the receipt of a second value of said binary signal; sampling means responsive to said oscillator means periodically sampling the incoming signal for generating for each sampling instant a signal having a first level or a second level dependent on whether the incoming signal at the time of sampling is greater or less than a given voltage level said sampling means comprising a sampling circuit for periodically sampling the incoming signal and comparator for comparing the samples with a given reference voltage level; shift register storage means responsive to said sampling means for storing a set of said signals having the first and second levels; and logic means responsive to said oscillator means to periodically sample said shift register storage means for generating said first or second value of said binary signal in accordance with particular given relationships among the levels of the signals stored in said shift register storage means.