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PHASE LOCKED LOOP

  • US 3,683,279 A
  • Filed: 12/17/1969
  • Issued: 08/08/1972
  • Est. Priority Date: 12/17/1969
  • Status: Expired due to Term
First Claim
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1. In an information transmission system having at least two spaced stations in communication with each other, a phase locked loop to stabilize the frequency of an oscillator disposed in one of said stations comprising:

  • said oscillator having an output frequency F;

    a source of reference signal having a frequency (N/M) F, where N and M are different integers greater than one such that (N/M) is a fractional number, said source being disposed in the other of said stations;

    first means disposed in said one of said stations coupled to perform the combined function of multiplying said frequency F by a factor (N/M) and comparing the phase relation between said multiplied frequency F and said reference signal received from said other of said stations to produce a phase control signal;

    second means disposed in said one of said stations to couple said control signal to said oscillator for frequency stabilization thereof;

    third means disposed in said other of said stations coupled to said source to sweep the frequency of said reference signal when the pull-in range of said loop is exceeded, said pull-in range being that range of frequency differences between the frequency of said reference signal and said output frequency of said oscillator where said loop is effective to perform the desired frequency stabilization; and

    fourth means disposed in said other of said stations coupled to respond to said reference signal received from said one of said stations to activate said third means when said reference signal has an amplitude less than a given threshold value indicating that said pull-in range is exceeded.

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