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Dropout detecting circuitry for a frequency modulated carrier, particularly for a video recorder

  • US 4,157,567 A
  • Filed: 08/26/1977
  • Issued: 06/05/1979
  • Est. Priority Date: 09/11/1976
  • Status: Expired due to Term
First Claim
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1. In a dropout detecting circuit for a frequency modulated carrier, particularly for a video recorder, in which the carrier is modulated over a definite frequency deviation range and is demodulated in an FM detector whose output voltage is used in an evaluation circuit to produce a switching pulse representing the dropout, the improvement comprising, in combination, a demodulator constituting said FM detector and providing a digital output signal having a first value within such deviation range of the carrier and a second value outside such deviation range;

  • and an evaluation circuit connected to said demodulator and producing said switching pulse responsive to only said second value of such digital output signal, said demodulator comprising a re-triggerable monoflop having a control input and an output; and

    an edge-triggered D flip-flop having first and second control inputs and having outputs;

    said FM carrier being applied to the control input of said retriggerable monoflop and to said first input of said edge-triggered D flip-flop;

    said output of said retriggerable monoflop being connected to said second control input of said D flip-flop;

    such switching pulse being derived at one of the outputs of said D flip-flop.

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