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AFC System for a synthesizer tuning system

  • US 4,208,741 A
  • Filed: 11/02/1978
  • Issued: 06/17/1980
  • Est. Priority Date: 11/02/1978
  • Status: Expired due to Term
First Claim
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1. An AFC system for a synthesizer-tuned television receiver comprising:

  • voltage-controllable reference oscillator;

    p1 voltage applying means coupled between the tuning control terminal of reference oscillator and between at least a first and a second source of tuning voltage, and a means for selecting the source of tuning voltage applied to the tuning control terminal;

    a crystal-controlled oscillator;

    a control circuit having an input coupled to the crystal-controlled oscillator and an output coupled to the reference oscillator;

    an AFC switch coupled to the control circuit, the AFC switch having an OFF condition and an ON condition whereby when the AFC switch is in the OFF condition the reference oscillator is continuously coupled by the control circuit to the crystal-controlled oscillator so that the reference oscillator is injection locked to the crystal-controlled oscillator and frequency of its output signal is equal to the frequency of the crystal-controlled oscillator; and

    an acquisition delay circuit having an input coupled to the voltage applying means and an output coupled to the control circuit so that when a source of tuning voltage is selected the reference oscillator is, for a period of time determined by the acquisition delay circuit, injection locked to the crystal-controlled oscillator and subsequently controlled by the voltage applied to the tuning control terminal through the voltage applying means.

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