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Phase-locked frequency synthesizer with means for restoring stability

  • US 3,921,094 A
  • Filed: 10/07/1974
  • Issued: 11/18/1975
  • Est. Priority Date: 10/07/1974
  • Status: Expired due to Term
First Claim
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1. A frequency synthesizer of the type in which a voltagecontrolled oscillator is disposed in a phase-locked loop including a phase and frequency comparator adapted to receive an external reference signal and a feedback signal to generate an error signal, means for applying the error signal to the control circuit of the voltage-controlled oscillator, means for deriving the feedback signal from the output signal generated by the voltage-controlled oscillator, and in which means are provided for altering the loop to facilitate frequency pull-in under some conditions of operation, characterized in that the deriving means includes frequency-count-down circuit means for deriving the feedback signal, said circuit means generating a substantially zero feedback signal when its frequency-response range is exceeded, and in that the loop altering means comprises semiconductive switching means for effectively disabling the loop between the output of the comparator and the voltage-controlled oscillator and for resetting the oscillator to a midpoint of its frequency range when the circuit means generates a substantially zero feedback signal.

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