[SI-LIST] Re: Power Planes - 3.3V / 2.5
- From: Terry Fox <tfox@xxxxxxxxx>
- To: jarbas@xxxxxxxxxxxxxxxx, <si-list@xxxxxxxxxxxxx>
- Date: Mon, 11 Jun 2007 15:42:15 -0700
Jarbas,
The return current path is a function of frequency.
From 10 MHz up it is gong to flow on the closest solid piece of copper or
possibly the two closest if it is between planes.
In general I prefer using a ground as the reference plane for 10MHz and up
because I generally have multiple grounds in a design and I can connect
them with a ground to ground stitching via to define the return current
path over a fairly wide frequency range.
The general idea is to keep the signal current and the return current
tightly coupled in order to avoid making a big EMI antennae.
Below 10MHz, the path is going to be the lowest impedance path for that
particular frequency.
TFox
tfox@xxxxxxxxx
At 01:02 PM 6/11/2007, Jarbas Aryel Nunes da Silveira wrote:
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>Hi,
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> I have some nets in a ten layer board, his types is SerDes 125 MHZ
>differentials pairs, from Marvell 88E1111 to an SFP Module. The 88E1111
>Marvell Transceiver is powered from 2.5V and SFP Module =E9 powered from
>3.3 V. What the power plane I must considerate to the reference this
>traces? 3.3V or 2.5V?
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>Best Regards.
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>Jarbas Aryel Nunes da Silveira, PMP
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>engenheiro eletricista
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>Fone: +55 (85) 3216.7916
>Fax: +55 (85) 3216.7864
>Skype: jarbas.aryel
>MSN: jarbas@xxxxxxxxxxxxxxxx =20
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>ISO 9001: 2000 - CMMI3
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> <http://www.atlantico.com.br/> www.atlantico.com.br
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