Differential transmission line with common mode notch filter

Patent metadata

Field	Value
Publication number	US-9118516-B1
Application number	US-201414473636-A
Country	US
Kind code	B1
Filing date	Aug 29, 2014
Priority date	Aug 29, 2014
Publication date	Aug 25, 2015
Grant date	Aug 25, 2015

Abstract

A differential transmission line with a common mode notch filter includes adjacently arranged, repeating differential transmission line pair sections. The sections have lengths that are each equal to half of an electric wavelength of a lowest frequency of a common mode electromagnetic wave to be suppressed during transmission of an electric signal over the differential transmission line. Each section includes a pair of conductors separated from one another by a spacing. The width of each conductor and the spacing between the conductors of each section vary over the length thereof according to a same pattern such that at every point over the length of each section a differential mode impedance of the differential transmission line is identical. A common mode impedance of the differential transmission line changes periodically in accordance with the lengths of the sections.

First claim

We claim:

1. A differential transmission line with a common mode notch filter, comprising:
a plurality of adjacently arranged, repeating differential transmission line pair sections, the sections having lengths that are each equal to half of an electric wavelength of a lowest frequency of a common mode electromagnetic wave to be suppressed during transmission of an electric signal over the differential transmission line, each section comprising a pair of conductors separated from one another by a spacing,
wherein a width of each conductor and the spacing between the conductors of each section vary over the length thereof according to a same pattern such that at every point over the length of each section a differential mode impedance of the differential transmission line is identical,
and wherein a common mode impedance of the differential transmission line changes periodically in accordance with the lengths of the sections.

2. The differential transmission line of claim 1 , wherein the same pattern is a discrete pattern, such that each section comprises a plurality of sub-sections,
wherein the width of each conductor and the spacing between the conductors are differently constant in each sub-section over the length of each section.

3. The differential transmission line of claim 2 , wherein the sub-sections of each section have different sub-section lengths.

4. The differential transmission line of claim 2 , wherein the sub-sections of each section have identical sub-section lengths.

5. The differential transmission line of claim 2 , wherein each section has exactly two sub-sections of different sub-section lengths.

6. The differential transmission line of claim 1 , wherein the same pattern is a continuous pattern, such that the width of each conductor of each section varies according to a first continuous function and the spacing between the conductors of each section varies according to a second continuous function.

7. The differential transmission line of claim 6 , wherein the first continuous function and the second continuous function are each sinusoidal.

8. The differential transmission line of claim 1 , wherein a profile of the sections is linear, such that the sections are linear and parallel to one another.

9. The differential transmission line of claim 1 , wherein a profile of the sections is angular, such that a plurality of sub-sections of at least one section includes a first sub-section and a second sub-section that are non-parallel to one another.

10. The differential transmission line of claim 1 , wherein a profile of the sections is curved, such that at least one section is curved.

11. A circuit board comprising:
a substrate; and
a differential transmission line on or within the substrate and comprising:
a plurality of adjacently arranged, repeating differential transmission line pair sections, the sections having lengths that are each equal to half of an electric wavelength of a lowest frequency of a common mode electromagnetic wave to be suppressed during transmission of an electric signal over the differential transmission line, each section comprising a pair of conductors separated from one another by a spacing,

wherein a width of each conductor and the spacing between the conductors of each section vary over the length thereof according to a same pattern such that at every point over the length of each section a differential mode impedance of the differential transmission line is identical,
and wherein a common mode impedance of the differential transmission line changes periodically in accordance with the lengths of the sections.

12. The circuit board of claim 11 , wherein the same pattern is a discrete pattern, such that each section comprises a plurality of sub-sections,
and wherein the width of each conductor and the spacing between the conductors are each differently constant in each sub-section over the length of each section.

13. The circuit board of claim 12 , wherein each section has exactly two sub-sections of different sub-section lengths.

14. The circuit board of claim 11 , wherein the same pattern is a continuous pattern, such that the width of each conductor of each section varies according to a first continuous function and the spacing between the conductors of each section varies according to a second continuous function.

15. The circuit board of claim 11 , wherein a profile of the sections is one of:
linear, such that the sections are linear and parallel to one another;
angular, such that a plurality of sub-sections of at least one section includes a first sub-section and a second sub-section that are non-parallel to one another;
curved, such that at least one section is curved.

16. An electronic device comprising:
a circuit board having a differential transmission line comprising a plurality of adjacently arranged, repeating differential transmission line pair sections, the sections having lengths that are each equal to half of an electric wavelength of a lowest frequency of a common mode electromagnetic wave to be suppressed during transmission of an electric signal over the differential transmission line, each section comprising a pair of conductors separated from one another by a spacing; and
one or more electrical components mounted on or within the circuit board,
wherein a width of each conductor and the spacing between the conductors of each section vary over the length thereof according to a same pattern such that at every point over the length of each section a differential mode impedance of the differential transmission line is identical,
and wherein a common mode impedance of the differential transmission line changes periodically in accordance with the lengths of the sections.

17. The electronic device of claim 16 , wherein the same pattern is a discrete pattern, such that each section comprises a plurality of sub-sections,
and wherein the width of each conductor and the spacing between the conductors are each differently constant in each sub-section over the length of each section.

18. The electronic device of claim 17 , wherein each section has exactly two sub-sections of different sub-section lengths.

19. The electronic device of claim 16 , wherein the same pattern is a continuous pattern, such that the width of each conductor of each section varies according to a first continuous function and the spacing between the conductors of each section varies according to a second continuous function.

20. The electronic device of claim 16 , wherein a profile of the sections is one of:
linear, such that the sections are linear and parallel to one another;
angular, such that a plurality of sub-sections of at least one section includes a first sub-section and a second sub-section that are non-parallel to one another;
curved, such that at least one section is curved.

Assignees

• Lenovo Entpr Solutions Singapore Pte Ltd
• IBM

Inventors

• Ao Eric R
• Campbell Alexander P
• Dignam Donald R
• Flint Stephen J
• Meng Jian

Classifications

• H04L25/0272

  Arrangements for coupling to multiple lines, e.g. for differential transmission · CPC title

• H04L25/0278 Primary

  Arrangements for impedance matching · CPC title

• H04L25/0276

  Arrangements for coupling common mode signals · CPC title