Triangular routing for high speed differential pair length matching

Patent metadata

Field	Value
Publication number	US-9690895-B2
Application number	US-201414309060-A
Country	US
Kind code	B2
Filing date	Jun 19, 2014
Priority date	Jun 19, 2014
Publication date	Jun 27, 2017
Grant date	Jun 27, 2017

Abstract

A method and apparatus for matching the lengths of traces of differential signal pairs. The method includes determining that a first trace is longer than a second trace and modifying the second trace so that the length is substantially equal to the length of the first trace. In some implementations, the second trace can be modified by replacing one or more sections of the trace with two line segments that are substantially equal in length and meet at a vertex that is less than 180 degrees.

First claim

What is claimed is:

1. A method for matching a length of a differential pair comprising:
determining, by a processor, that a first length of a first signal trace is longer than a second length of a second signal trace, wherein the first signal trace and the second signal trace are routed on substantially parallel conductive paths;
modifying, by the processor, the second signal trace so that the second length is substantially equal to the first length of the first signal trace, wherein the modifying comprises:
replacing, by the processor, one or more sections of the second signal trace with a first line segment and a second line segment, the first line segment and the second line segment each having a first end and a second end, wherein the second end of the first line segment meets the first end of the second line segment to create a triangular vertex.

2. The method of claim 1 , wherein the first line segment and the second line segment define a lateral deviation from the replaced one or more sections, wherein the lateral deviation is less than a spacing between the first signal trace and the second signal trace.

3. The method of claim 1 , wherein the first line segment and the second line segment extend the second signal trace in a direction away from the first signal trace, and wherein a first angle exists between the first line segment and a line corresponding to the replaced one or more sections and a second angle exists between the second line segment and the line corresponding to the replaced one or more sections.

4. The method of claim 3 , wherein the first angle and the second angle are substantially equivalent.

5. The method of claim 3 , wherein the first angle and the second angle are between 0 degrees and 35 degrees.

6. The method of claim 3 , further comprising:
subtracting the second length from the first length to determine a desired compensation length;
calculating a permitted lateral deviation using a spacing between the first signal trace and the second signal trace;
calculating a length for the first line segment and the second line segment, wherein the length is based on the permitted lateral deviation and the first angle;
determining a number of sections to replace on the second signal trace to achieve the desired compensation length.

7. The method of claim 6 , wherein the permitted lateral deviation is between 5% and 20% of the spacing between the first signal trace and the second signal trace.

8. The method of claim 1 , wherein the first signal trace and the second signal trace are routed on a substrate of an integrated circuit.

9. A signal transmission apparatus, comprising:
a first signal trace; and
a second signal trace, the first signal trace and the second signal trace configured to be routed on substantially parallel conductive paths, the second signal trace including one or more length matching sections, the one or more length matching sections including:
a first line segment having a first end and a second end; and
a second line segment having a first end and a second end, the second end of the first line segment meeting the first end of the second line segment to create a triangular vertex, wherein the second signal trace forms a lateral deviation with respect to the first signal trace.

10. The signal transmission apparatus of claim 9 , wherein the lateral deviation is less than a spacing between the first signal trace and the second signal trace.

11. The signal transmission apparatus of claim 9 , wherein the first line segment and the second line segment replace a portion of the second signal trace, and wherein a first routing angle exists between the first line segment and a line corresponding to the replaced portion and wherein the first routing angle is between 0 degrees and 35 degrees.

12. The signal transmission apparatus of claim 9 , wherein the one or more length matching segments cause the first signal trace and the second signal trace to have substantially equal lengths.

13. The signal transmission apparatus of claim 9 , wherein the apparatus is a printed circuit board including one or more pockets of resin material, and wherein the first line segment and the second line segment do not overlap the one or more pockets of resin material.

14. The signal transmission apparatus of claim 13 , wherein the printed circuit board comprises a plurality of routing layers and wherein the first signal trace and the second signal trace are routed on one or more of the plurality of routing layers.

15. A non-transitory computer-readable storage medium having stored therein instructions which, when executed by a processor, cause the processor to perform operations for matching a length of a differential pair, the operations comprising:
determining that a first length of a first signal trace is longer than a second length of a second signal trace, wherein the first signal trace and the second signal trace are routed on substantially parallel conductive paths;
modifying the second signal trace so that the second length is substantially equal to the first length of the first signal trace, wherein the modifying comprises:
replacing one or more sections of the second signal trace with a first line segment and a second line segment, the first line segment and the second line segment each having a first end and a second end, wherein the second end of the first line segment meets the first end of the second line segment to create a triangular vertex.

16. The non-transitory computer-readable medium of claim 15 , wherein the first line segment and the second line segment define a lateral deviation from the replaced one or more sections, wherein the lateral deviation is less than a spacing between the first signal trace and the second signal trace.

17. The non-transitory computer-readable medium of claim 15 , wherein the first line segment and the second line segment extend the second signal trace in a direction away from the first signal trace, and wherein a first angle exists between the first line segment and a line corresponding to the replaced one or more sections and a second angle exists between the second line segment and the line corresponding to the replaced one or more sections.

18. The non-transitory computer-readable medium of claim 17 , wherein the first angle and the second angle are substantially equivalent, and wherein the first angle and the second angle are between 0 degrees and 35 degrees.

19. The non-transitory computer-readable medium of claim 17 , further comprising:
subtracting the second length from the first length to determine a desired compensation length;
calculating a permitted lateral deviation using a spacing between the first signal trace and the second signal trace;
calculating a length for the first line segment and the second line segment, wherein the length is based on the permitted lateral deviation and the first angle;
determining a number of sections to replace on the second signal trace to achieve the desired compensation length.

20. The non-transitory computer-readable medium of claim 19 , wherein the permitted lateral deviation is between 5% and 20% of the spacing between the substantially parallel conductive paths.

Assignees

• Cisco Tech Inc

Inventors

• Shen Lin
• Xiong Yongming
• Ong Stephen
• Mahmood Shahbaz

Classifications

• H05K1/0216

  Reduction of cross-talk, noise or electromagnetic interference (grounding H05K1/0215) · CPC title

• G06F30/394 Primary

  Routing (G06F30/396 takes precedence) · CPC title

• H05K2201/09236

  Parallel layout · CPC title

• H01P3/081

  Microstriplines · CPC title

• H04L25/027

  specifically for telegraph signals (induction coil interrupters H01H51/34; dynamo-electric generators H02K) · CPC title