Balun

• US 4,717,896 A
• Filed: 03/21/1985
• Issued: 01/05/1988
• Est. Priority Date: 03/21/1985
• Status: Expired due to Term

• Current Assignee: AND Yet, Inc.
• Original Assignee: AND Yet, Inc.
• Inventors: Graham, Martin H.
• Primary Examiner(s): LaRoche, Eugene R.
• Assistant Examiner(s): LEE, BENNY T
• Application Number:
  US06/715,129
• Time in Patent Office: 1,020 Days
• Field of Search: 333/25, 333/26, 333/32, 333/181, 333/177, 336/180, 336/182, 336/186, 336/170, 336/220, 343/820-822, 343/859, 343/860, 343/862
• US Class Current: 333/25
• CPC Class Codes: H03H 7/42 Networks for transforming balanced signals into unbalanced signals and vice versa, e.g. baluns

Abstract

The present invention comprises a balun for intercoupling an at least partially unbalanced line and a substantially balanced line having similar line impedances which is capable of passing differential signals over a wide bandwidth while substantially attenuating any common mode signals. The balun comprises a pair of transformers with bifilar windings, each connected as a choke. Each conductor of the unbalanced line is coupled to a different one of two substantially identical inductances of the first transformer and the other side of each inductance is coupled through the second transformer to a different one of the two conductors of the balanced line. Each of the connections between the two transformers is coupled to ground with a substantially identical capacitance. The capacitance in conjunction with the inductance acts to filter out the common mode signals while allowing the differential mode signals to pass through the balun. The capacitance is coupled to each transmission line by a transformer with sufficient inductance to prevent differential signals in either direction from being shunted to ground. Preferably, a resistor is added in parallel to each of the capacitances to provide for common mode attenuation at the resonant frequency of the system capacitance and inductances.

Claims

1. A balun for coupling a signal of a predetermined bandwidth between an at least partially unbalanced two-conductor line having a first and a second conductor and a balanced two-conductor line having a first and second conductor, comprising:

a first inductance adapted to have a first lead coupled to the first conductor of said unbalanced line;

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

a first capacitance coupling said second lead of said first inductance to ground;

a second capacitance coupling said second lead of said second inductance to ground, said second capacitance being substantially equal in value to said first capacitance;

a first resistance coupled in parallel with said first capacitance; and

a second resistance coupled in parallel with said second capacitance, said second resistance being substantially equal in value to said first resistance;

the combined parallel impedance of said first and second resistances and said first and second capacitance being lower than the open circuit impedance of said first and second inductances, and said third and fourth inductances over said predetermined bandwidth, and the series impedance of said first resistance and capacitance, and said second resistance and capacitance being higher than the impedance of said lines.

2. A balun for coupling a plurality of at least partially unbalanced two-conductor lines to a plurality of balanced two-conductor lines, each partially unbalanced two-conductor line having a first and a second conductor and each corresponding balanced two-conductor line having a first and second conductor, comprising:

a first inductance adapted to have a first lead coupled to the first conductor of a first one of said unbalanced lines;

a second inductance adapted to have a first lead coupled to the second conductor of said first one of said unbalanced lines and to a second conductor of a second unbalanced line, said seciond inductance sharing a common core with said first inductance and having a substantially equal value to said first inductance;

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

a fourth inductance coupled at a first lead to a second lead of said first inductance and adapted to have a second lead coupled to a first conductor of a first one of said balanced lines;

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

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

a first capacitance coupling said second lead of said first inductance to ground;

a second capacitance coupling said second lead of said second inductance to ground, said second capacitance being substantially equal in value to said first capacitance;

a third capacitance coupling said second lead of said third inductance to ground, said third capacitance being substantially equal in value to said first capacitance;

a first resistance coupled in parallel with said first capacitance;

a second resistance coupled in parallel with said second capacitance, said second resistance being substantially equal in value to said first resistance; and

a third resistance coupled in parallel with said third capacitance, said third resistance being substantially equal in value to said first resistance.