Differential transmission line shielded by two or more spaced groups of shields

1. An integrated circuit comprising:

a pair of differential transmission lines formed in a first layer of metal of the integrated circuit, the pair comprising a first transmission line and a second transmission line, the first transmission line configured to carry a first signal complementary to a second signal carried by the second transmission line, each of the first transmission line and the second transmission comprising a length and a width generally parallel to the first metal layer, wherein the length is greater than the width and current flowing in the first transmission line and second transmission line flows in a direction generally parallel to the length; and

a plurality of shields, each shield comprising:

an upper-side tile formed in a second metal layer of the integrated circuit adjacent to the first metal layer, the upper-side tile having a length measured in an axis parallel to the second metal layer and perpendicular to the length of the differential transmission lines and a width measured in an axis perpendicular to the length thereof and parallel to the length of the differential transmission lines;

a lower-side tile formed in a third metal layer of the integrated circuit adjacent to the first metal layer and non-adjacent to the second metal layer, the lower-side tile having a length measured in an axis parallel to the third metal layer and perpendicular to the length of the differential transmission lines and a width measured in an axis perpendicular to the length thereof and parallel to the length of the differential transmission lines; and

at least one via configured to electrically couple the upper-side tile at an end of the length of the upper-side tile to the lower-side tile and at an end of the length of the lower-side tile;

wherein the plurality of shields comprises a plurality of groups of two or more shields, each group comprising a similar geometry of two or more shields, and each group spaced from adjacent groups by an approximately equal distance along the length of the differential transmission lines, wherein the approximately equal distance between each group is greater than a spacing between the two or more shields within each group.

2. The integrated circuit of claim 1 , wherein each shield is electrically floating.

3. The integrated circuit of claim 1 , wherein each shield is not electrically coupled to any other shields of the plurality of shields.

4. The integrated circuit of claim 1 , wherein each of the width of the upper-side tile and the width of the lower-side tile is shorter than a wavelength of a signal carried by the differential transmission lines.

5. The integrated circuit of claim 1 , wherein at least one of the similar geometry of each group and the spacing between adjacent groups is configured to provide a desired shielding density for the differential transmission lines.

6. The integrated circuit of claim 5 , wherein the desired shielding density is selected based on a desired electrical isolation of the differential transmission lines.

7. The integrated circuit of claim 5 , wherein the desired shielding density is selected based on a desired electrical property of the differential transmission lines.

8. The integrated circuit of claim 7 , the desired electrical property comprising one of an effective transmission length of the differential transmission lines, a capacitance of the differential transmission lines, a signal propagation delay of the differential transmission lines, a drain current associated with the differential transmission lines, and a power consumption associated with the differential transmission lines.

9. A method comprising:

forming a pair of differential transmission lines in a first layer of metal of an integrated circuit, the pair comprising a first transmission line and a second transmission line, the first transmission line configured to carry a first signal complementary to a second signal carried by the second transmission line, each of the first transmission line and the second transmission comprising a length and a width generally parallel to the first metal layer, wherein the length is greater than the width and current flowing in the first transmission line and second transmission line flows in a direction generally parallel to the length; and

forming a plurality of shields, each shield comprising:

an upper-side tile formed in a second metal layer of the integrated circuit adjacent to the first metal layer, the upper-side tile having a length measured in an axis parallel to the second metal layer and perpendicular to the length of the differential transmission lines and a width measured in an axis perpendicular to the length thereof and parallel to the length of the differential transmission lines;

a lower-side tile formed in a third metal layer of the integrated circuit adjacent to the first metal layer and non-adjacent to the second metal layer, the lower-side tile having a length measured in an axis parallel to the third metal layer and perpendicular to the length of the differential transmission lines and a width measured in an axis perpendicular to the length thereof and parallel to the length of the differential transmission lines; and

at least one via configured to electrically couple the upper-side tile at an end of the length of the upper-side tile to the lower-side tile and at an end of the length of the lower-side tile;

wherein the plurality of shields comprises a plurality of groups of two or more shields, each group comprising a similar geometry of two or more shields, and each group spaced from adjacent groups by an approximately equal distance along the length of the differential transmission lines, wherein the approximately equal distance between each group is greater than a spacing between the two or more shields within each group.

10. The method of claim 9 , wherein each of the width of the upper-side tile and the width of the lower-side tile is shorter than a wavelength of a signal carried by the differential transmission lines.

11. The method of claim 9 , further comprising forming the each shield such that each shield is electrically floating.

12. The method of claim 9 , further comprising forming each shield such that each shield is not electrically coupled to any other shields of the plurality of shields.

13. The method of claim 9 , wherein at least one of the similar geometry of each group and the spacing between adjacent groups is configured to provide a desired shielding density for the differential transmission lines.

14. The method of claim 13 , further comprising selecting the desired shielding density based on a desired electrical property of the differential transmission lines.

15. The method of claim 14 , the desired electrical property comprising one of an effective transmission length of the differential transmission lines, a capacitance of the differential transmission lines, a signal propagation delay of the differential transmission lines, a drain current associated with the differential transmission lines, and a power consumption associated with the differential transmission lines.

16. The method of claim 13 , further comprising selecting the desired shielding density based on a desired electrical isolation of the differential transmission lines.