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FM Television signal receiving circuit

  • US 4,417,279 A
  • Filed: 02/11/1982
  • Issued: 11/22/1983
  • Est. Priority Date: 02/16/1981
  • Status: Expired due to Term
First Claim
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1. A receiving circuit for a television receiver for receiving an FM-modulated television signal, comprising:

  • a mixer circuit, supplied with an FM-modulated television signal of a first frequency band and a local oscillation signal from a local oscillator circuit, for converting said FM-modulated television signal of the first frequency band into a television signal of a second frequency band in accordance with said local oscillation signal;

    the local oscillator circuit generating the local oscillation signal and applying it to said mixer circuit, a frequency of the local oscillation signal being varied in accordance with a tuning voltage supplied from an external source which represents a channel of the television signal to be received;

    an FM detector circuit for FM-detecting the FM-modulated television signal of the second frequency band from said mixer circuit and producing a television composite video signal;

    a video amplifier circuit for amplifying the composite video signal from said FM detector circuit;

    a sync separation circuit for separating a sync signal from the composite video signal applied thereto from said video amplifier circuit and outputting only said sync signal;

    a sampling circuit, supplied with the composite video signal from said FM detector circuit and the sync signal from said sync separation circuit, for picking up the sync signal voltage of said composite video signal in accordance with said sync signal from said sync separation circuit, said sampling circuit producing an output voltage corresponding to the frequency spectrum of the sync signal of the television signal of the second frequency band, and applying it to a hold circuit; and

    the hold circuit for holding the output voltage signal from said sampling circuit for a predetermined period, producing a DC voltage corresponding to the output voltage signal from said sampling circuit, and applying said DC voltage to said local oscillator circuit, said DC voltage being superimposed on the tuning voltage applied to said local oscillator circuit and controlling the oscillation frequency of said local oscillator circuit such that the frequency spectrum of the sync signal of the television signal of the second frequency band takes a predetermined value.

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