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Receiving circuit

  • US 6,236,688 B1
  • Filed: 02/26/1999
  • Issued: 05/22/2001
  • Est. Priority Date: 11/30/1994
  • Status: Expired due to Term
First Claim
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1. A receiving circuit comprising:

  • first and second frequency converting circuits for accepting a received signal obtained through an antenna;

    a local frequency signal generating circuit coupled to said first and second frequency converting circuits for generating middle frequencies between a radio carrier frequency of said received signal and radio carrier frequencies of adjacent upside and downside channels and further for outputting the upside frequency of the upside and downside two wave frequencies as a conversion frequency input to said first frequency converting circuit and for outputting the downside frequency thereof as a conversion frequency input to said second frequency converting circuit;

    first and second integrating circuits, serving additionally as low-pass filters, for receiving outputs of said first and second frequency converting circuits through input lines;

    first and second buffer amplifiers for receiving outputs of said first and second integrating circuits;

    first and second transformers having the same construction and having primary coils whose one ends accepts outputs of said first and second buffer amplifiers, the other ends of said primary coils of said first and second transformers being grounded in the form of alternating currents, and secondary coils of said first and second transformers being coupled in parallel to each other in accordance with polarities of said primary coils and one ends of said secondary coils equal in polarity to said primary coils is used as an output terminal while the other ends of said secondary coils are grounded;

    a third buffer amplifier for accepting an output from said first and second transformers;

    a frequency offset circuit for removing a frequency offset remaining in an output of said third buffer amplifier; and

    a filter for removing an unnecessary frequency component remaining in an output of said frequency offset.

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