Re: [SI-LIST] : Number of GND/Power pins in a connector ?

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From: Scott McMorrow (scott@vasthorizons.com)
Date: Thu Mar 23 2000 - 10:55:34 PST


Stuart,

"It depends" is the correct answer.

The best way to size the number of ground and power pins in
a connector is to simulate the regions on either side of the
connector. The connector model should be fully coupled for
all pins including power and ground. You should grid the ground
and power planes around the connector edge and within the
grid include the decoupling capacitors. A connector swath
should be simulated with data transmitted in both directions
(if bidirectional) and driven by worst case driver edge rates into
transmission lines which are referenced to the non-ideal power
and ground grid. Multiple data patterns should be simulated
for worst case pattern sensitivity.

These sorts of simulations will answer several questions:

How much data skew and jitter is caused by connector crosstalk,
and return path effects for each ground/power pattern?

What happens when a signal is referenced to a ground plane
on one side of the connector and to a power plane on the
other side?

How much noise is induced by data switching into the ground and
power grids on either side of the connector?

What is the worst case instantaneous voltage differential
across the ground pins on either side of the connector?

What is the worst case instantaneous voltage differential
across the power pins on either side of the connector?

And for bonus points:

If you have accurate modeling of the power switching currents of
the devices on either side of the connector, you can simulate the
worst case connector and plane noise due to power transients
and data switching transients.

Depending on the edge rate and the quality of the connector you
may find that although you need few power and ground pins to
facilitate clean power delivery, you may need many more power
and ground pins to facilited clean signal delivery.

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

Stuart Adams wrote:

> How do I calculate the number of ground and power > pins I need in a board-to-board connector. > > The number of grounds is a function of switching > current and how many signals will switch at the same > time, correct ? > > More grounds is always better but what about power pins ?? > > If one or two pins are sufficient to carry the max steady > state current and my board is well bypassed with bulk and > ceramic caps, is there a need for alot more power pins ? > > -- Stuart > > **** To unsubscribe from si-list or si-list-digest: send e-mail to majordomo@silab.eng.sun.com. In the BODY of message put: UNSUBSCRIBE si-list or UNSUBSCRIBE si-list-digest, for more help, put HELP. > si-list archives are accessible at http://www.qsl.net/wb6tpu > ****

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