[SI-LIST] Re: LC filters on SDRAM signal lines
- From: Cosmin Iorga <ci249534@xxxxxxxxx>
- To: "David Carney \(Neenah\)" <David.Carney@xxxxxxxxxx>, "si-list@xxxxxxxxxxxxx" <si-list@xxxxxxxxxxxxx>
- Date: Fri, 24 Jun 2011 17:07:36 -0700 (PDT)
David,
I would like to add a comment in addition to all good advice that you have
received so far: I suggest you run a few experiments to figure out if the 75MHz
coupling occurs through radiation or through power distribution. If it turns
out to happen through power distribution then adding LC filters will not do any
good since the dynamic currents will still flow through the power distribution
impedance to/from the on-chip drivers. Hope this helps.
Cosmin Iorga, PhD
NoiseCoupling.com
http://www.noisecoupling.com
________________________________
From: David Carney (Neenah) <David.Carney@xxxxxxxxxx>
To: si-list@xxxxxxxxxxxxx
Sent: Friday, June 24, 2011 8:47 AM
Subject: [SI-LIST] LC filters on SDRAM signal lines
I'm working on an embedded product with a GSM cellular module. The
module is picking up broadband noise in the GSM850 band (869-894 MHz) at
levels of approximately -90dBm to -100dBm from the board it is on. The
noise is causing BER levels that are too high (fails some tests). The
source of the noise has been tracked to a processor SDRAM bus interface
running at 75 MHz clock frequency. This processor and SDRAM are
physically close to the GSM module on the board. One of the many
suggestions for mitigating this problem that we are considering is to
add LC filters to all of the SDRAM data lines such as the following
example parts:
Murata NFM18PS105R0J3
(http://search.murata.co.jp/Ceramy/image/img/PDF/ENG/L0111S0111NFM18PS.p
df)
TDK MEA1608PH (http://www.tdk.co.jp/tefe02/e9621_mea_signal_1.pdf)
These parts are recommended for LCD interfaces. Does anyone have
experience using these on SDRAM interfaces? Is this an effective way to
solve the problem? What considerations do we need to account for in
using them? Has anyone modeled these parts for signal integrity
simulations? We have been told by Murata that no model is available.
What modeling approach did you use?
Thanks.
David T. Carney P.E.
Senior Design Engineer
Plexus Engineering Solutions
Neenah Design Center
920.751.5646
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