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Balun

  • US 4,800,344 A
  • Filed: 08/27/1987
  • Issued: 01/24/1989
  • Est. Priority Date: 03/21/1985
  • Status: Expired due to Term
First Claim
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1. A balun which substantially attenuates common mode signals without significantly attenuating differential mode signals for coupling an at least partially unbalanced line having at least a first and a second conductor to a balanced line having at least a first and a second conductor, comprising:

  • a first inductance adapted to have a first lead coupled to said first conductor of said unbalanced line and adapted to have a second lead coupled to said second conductor of said unbalanced line;

    a second inductance sharing a common core with said first inductance and having a substantially equal value to said first inductance;

    a third inductance having a first coupled to a first lead of said second inductance and adapted to have a second lead coupled to said first conductor of said balanced line;

    a fourth inductance having a first lead coupled to a second lead of said second inductance and adapted to have a second lead coupled to said second conductor of said balanced line, said fourth inductance sharing a common core with said third inductance and having a substantially equal value to said third inductance; and

    a first capacitance coupling said first lead of said second inductance to a ground potential, and a second capacitance coupling said second lead of said second inductance to the ground potential for substantially attenuating the common mode signals without significantly attenuating the differential mode signals, wherein the common mode signals are one-half the sum of the voltage between the first conductor of the unbalanced line and the ground potential and the voltage between the second conductor of the unbalanced line and the ground potential and wherein the differential mode signals are the difference between the voltage from the first conductor of the unbalanced line to the ground potential and the voltage from the second conductor of the unbalanced line to the ground potential,said first and second capacitances satisfy the equation 1/(2ω

    C)<

    <

    ω

    Loc to substantially attenuate the common mode signals and satisfy the equation 1/(ω

    C/2)>

    >

    ω

    Lsc to avoid attenuating the highest frequencies of the differential mode signals used for transmission, where Loc is the open circuit inductance, Lsc is the short circuit inductance and ω

    is 2 π

    times the highest frequency of the differential mode signals used for transmission.

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