[SI-LIST] Return current at board transitions
- From: "Joel Brown" <joel@xxxxxxxxxx>
- To: "SI-List" <si-list@xxxxxxxxxxxxx>
- Date: Mon, 29 Dec 2008 16:36:02 -0800
Two boards are mated together with impedance controlled high speed
connectors.
One board has diff pairs with a large dielectric spacing so a large
percentage of the return currents flow in the opposite trace of the diff
pair.
The other board has a small dielectric height so a large percentage of the
return currents flow in the adjacent ground planes.
What happens at the transition? How does the return current change from
flowing in the opposite signal trace to a ground plane?
Is this a discontinuity even though the impedances are the same? Does it not
matter since the differential currents cancel?
Thanks - Joel
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