[SI-LIST] Re: Plane Isolation
- From: Hirshtal Itzhak <ihirshtal@xxxxxxxxxx>
- To: Scott McMorrow <scott@xxxxxxxxxxxxx>
- Date: Sun, 26 Jun 2011 08:32:55 +0200
Hello Scott,
Thanks for the tip.
Just one question/clarification: My concern is NOT for the Analog signal
contaminating the digital signal, but vice versa. Since the digital
signal has much more BW, the saturation length will be much smaller than
you have indicated, and exactly the same as for digital to digital
noise, e.g. on the order of several hundredths of mils or several inches
at the most.
I assume this makes no difference as for 75dB number you have quoted. Am
I right?
Thanks
Itzhak Hirshtal
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On Behalf Of Scott McMorrow
Sent: Thursday, June 23, 2011 5:02 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Plane Isolation
Itzhak
there is no one number, since you need about 1000" of trace coupling to
fully saturate crosstalk through a plane at 5 MHz. IIRC for 30" of
trace coupling in an analog video switch board we consulted on about 15
years ago, it took 1oz copper to achieve 75 dB of isolation. This was
verified through measurement and modeling. The only tool I know of that
is reasonably capable of modeling field penetration through copper for
traces is Ansoft 2D FEM quasi-static solver, which now a part of the
Ansoft 3D package. The match between measurement and modeling was
actually quite amazing. HFSS would also be able to do this sort of
modeling, you'd have to create a short coupled section, and then
concatenate it for the length of trace coupling that you have in your
system.
regards,
Scott
Scott McMorrow
Teraspeed Consulting Group LLC
121 North River Drive
Narragansett, RI 02882
(401) 284-1827 Business
(401) 284-1840 Fax
http://www.teraspeed.com
Teraspeed(r) is the registered service mark of
Teraspeed Consulting Group LLC
On 6/23/2011 3:07 AM, Hirshtal Itzhak wrote:
> Hi all,
>
>
> I want to route hi-speed digital signals on a layer right above some
> sensitive analog signals (low freq of up to 7MHz). The analog signals
> will be routed side-by-side with their analog GND traces along it.
>
>
>
> To eliminate the possibility of noise induced from the digital to the
> analog signals, I intend to separate the 2 signal layers by a number
of
> Power/GND planes.
>
>
>
> Is there a known number for the attenuation that such a plane yields
> between the signals? Is there a formula for calculating the
attenuation?
>
>
>
> Thanks
>
> Itzhak Hirshtal
>
>
>
>
>
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intended only for
the use of the intended addressee thereof. If you are not the intended
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