[SI-LIST] Re: differential pairs on backplane connectors
- From: Julian Ferry <julian.ferry@xxxxxxxxxx>
- To: "'Stephen.Greenhalgh@xxxxxxxxxxx'" <Stephen.Greenhalgh@xxxxxxxxxxx>, "Si-List (E-mail)" <si-list@xxxxxxxxxxxxx>
- Date: Thu, 5 Jan 2006 14:06:11 -0500
I can't read the minds of my competitors who designed the connectors you
mentioned (although I CAN read their Patents...). But I might be able to add
some insight based on some of our connector designs.
For optimal electrical performance, it is usually best to position a
differential pair horizontally in a connector. There are some exceptions,
but not many. But there are often non-electrical reasons that can make a
vertical pairing attractive. Two good examples are signal density and
connector cost. In some cases, the non-electrical benefits of a vertical
paring can off set any electrical penalties.
Also, some of the skew inherent in a vertical pairing can be compensated for
in the pcb. Some can also be compensated within the connector itself, by
judicious use of materials and geometries.
The bottom line is that each particular application has its own electrical
requirements, and in many cases, a vertical pair is "good enough".
Julian Ferry
High Speed Engineering Manager
Samtec, Inc
Mechanicsburg, PA
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of Stephen Greenhalgh
Sent: Thursday, January 05, 2006 6:13 AM
To: Si-List (E-mail)
Subject: [SI-LIST] differential pairs on backplane connectors
When using standard pin matrix backplane connectors (for example, 2mm hard
metric), the conventional wisdom was to assign two adjacent pins in the same
row for a differential pair. This meant that the right angle (daughter
board) connections were of equal length and geometry.
However, the newer connectors, designed specifically for differential pairs
(for example, FCI Airmax VS, Amphenol GcX or ERNI ERmet ZD) use pairs of
pins in the same column. This seems surprising, since it appears to mean
that there is an inherent imbalance between the two connections. Perhaps
this is taken into account in the connector design? Can anyone provide an
explanation or clarification, please?
Stephen Greenhalgh
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