Re: [SI-LIST] : Connector pin pwr/gnd ratio

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From: Scott McMorrow (scott@vasthorizons.com)
Date: Mon Nov 13 2000 - 15:37:07 PST


Actually, the solid bar is not the asymptote.
There are cases with many connectors where
additional grounds are needed to shield adjacent
conductors. This is dependent upon the amount of
crosstalk that can be tolerated and the amount of
jitter across the connector that can be tolerated.

Just because the connector is controlled impedance
does not mean that there is not coupling between
adjacent signals or adjacent pairs of signals.
Jitter on differential pairs can become quite high
going through a connector if coupling to the adjacent
pair is not considered.

There is no general rule for the signal to power ratio
of a connector. It just depends on how much quiet
signal crosstalk you can tolerate and/or how much
jitter (skew) you can tolerate due to neighbors
switching.

regards,

scott

--
Scott McMorrow
Principal Engineer
SiQual, Signal Quality Engineering
18735 SW Boones Ferry Road
Tualatin, OR  97062-3090
(503) 885-1231
http://www.siqual.com

Charles Grasso wrote:

> The allocation of grounds with respect to any number of signals is mainly > based > on rise time (hence frequency content). That is to say the faster the rise > time the > more grounds you need - the asymptote being a solid "bar" connection found > in many impedace controlled connectors. > > ----- Original Message ----- > From: "Peterson, James F (FL51)" <james.f.peterson@honeywell.com> > To: <si-list@silab.eng.sun.com> > Sent: Monday, November 13, 2000 6:57 AM > Subject: [SI-LIST] : Connector pin pwr/gnd ratio > > > Hello, > > > > I'm looking for some information on what the pwr/gnd ratio should be for a > > board's connector. (I know there is something in the archives, but I > > couldn't find it.) > > > > Someone said a rule of thumb is a 3 to 1 ratio, but I'm not sure what that > > is based on. > > > > So let's say for example I have 85 connector pins for 3.3v, 2.5v and gnd. > > How would you distribute? and why? > > > > thanks > > Jim > > > Jim Peterson > > > james.f.peterson@honeywell.com > > > Honeywell Space Systems > > > M/S 934-5 > > > 13350 U.S. Hwy 19 N. > > > Clearwater FL, 33764-7290 > > > Office : 727-539-2719 > > > Fax : 727-539-2183 > > >

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