[SI-LIST] Re: DDR Termination

Hi Steve,

Like many interfaces, the answer is it depends
as there are often many tradeoffs to your=20
termination scheme.  You will have more flexibility
than most as you have a single module, rather
than multiple modules with a variety of loads.
You need to take a look at the signal integrity
along with your available board real estate, power,
etc.  Odds are you will be OK with a series only=20
approach. However, as speeds increase it is worth
the time to do your due diligence, run a sim with
your two schemes, and convince yourself that you
have the margin that you need.  There is such a=20
thing as over design.

Best Regards,

Michael Greim
Platform Engineering
Newisys, Inc.
512-340-9050, ext 232    (V)
512-740-9097                  (C)

We will either find a way or make one     -Hannibal

And all this science they don't understand
is just my job six days a week........

The time is gone, the email's over
Thought I'd something more to say.......
=20

-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Santangelo, Steven
Sent: Friday, March 25, 2005 10:55 AM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] DDR Termination


Hi,

I'm looking at a DDR interface which consists of a controller and a =3D
single SODIMM module.  In the past we've successfully simulated, built =
=3D
and tested this interface using only series terminations but have always =
=3D
run it fairly slow, 100MHz or 133MHz.   As we crank up the clock on =3D
future designs I'm starting to wonder if we should switch to the more =
=3D
standard series+parallel termination scheme.  Aside from the increased =
=3D
over and undershoot and any resulting EMI issues, I don't see a big =3D
difference between the 2 approaches.  If anything, the series only =3D
approach appears to give me better noise margin due to the increased =3D
swing.  Should I be concerned about using the series termination only =
=3D
approach when running at higher speeds, say 166MHz or 200MHz?  What =3D
areas should I be concerned about?

Thanks

Steve
 =3D20
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 =20

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