Re: [SI-LIST] : Return path for stripline, two ground planesor one power and one ground?

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From: Scott McMorrow (scott@vasthorizons.com)
Date: Mon Apr 03 2000 - 14:01:37 PDT


Mark,

Stackup 1 is superior as it reduces the mounted loop inductance
of decoupling capacitors ... along with your other good reasons.
The only issue with Stackup 1 would be isolation of the S1 and S2
routing layers. This can be done by routing them orthogonal and
checking final routing for crosstalk.

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

Mark Nass wrote:

> Assuming you had an 8 layer board with the drivers described below. > What > stackup would you recommend, 1 or 2 below? Stackup #1 would seem to be > better > for lower power plane impedance(assuming 4-4.5 mils between planes). > This > would also provide good board capacitance and allow the AC currents to > switch layers > as needed for the reasons you discuss below. The application I am > thinking > of, DDR, would also have DIMM connectors on this board and the signals > would need to > pass thru connectors. It seems like board capacitance of stackup #1 > would help > AC return currents that may have to switch layers near the DIMM > connectors also. > > ............ Stackup 1 .................. > Top -- > GND ------ > PWR ------ > S1 -- > S2 -- > GND ------ > PWR ------ > Bot -- > > ............ Stackup 2 .................. > Top -- > GND ------ > S1 -- > PWR ------ > GND ------ > S2 -- > PWR ------ > Bot -- > > ............Text deleted ............... >

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