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AFT circuit for CATV receiver system

  • US 4,855,835 A
  • Filed: 04/28/1988
  • Issued: 08/08/1989
  • Est. Priority Date: 08/14/1987
  • Status: Expired due to Fees
First Claim
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1. An AFT circuit of a CATV receiver system of a double conversion method having a first local oscillator and a second local oscillator and a first mixer and a second mixer respectively supplied with oscillation outputs from said first and second local oscillators such that a reception signal is sequentially subjected to a frequency conversion by use of said first and second mixers so as to attain a second intermediate frequency signal of a predetermined frequency comprising:

  • control voltage generate means for outputting a control voltage depending on a frequency fluctuation of said second intermediate frequency signal;

    select means for selecting either said control voltage or a constant voltage and for supplying the selected voltage as an oscillation frequency control voltage controlling an oscillation frequency of said second local oscillator to said second local oscillator;

    integrate means for integrating said oscillation frequency control voltage so as to produce as an output therefrom an integrated voltage attained through the integration; and

    voltage compare means for comparing said integrated voltage with a reference voltage so as to supply a result of the comparison to said select means whereinsaid select means operative based on said compare result from said voltage compare means supplies said control voltage to said second local oscillator when said integrated voltage is higher than said reference voltage and supplies said constant voltage to said second local oscillator when said integrated voltage is lower than said reference voltage.

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