[SI-LIST] Re: mDDR (200MHz) without Series Termination
- From: "Xu, Catherine (ICS)" <xu@xxxxxx>
- To: Embedded <hw_si@xxxxxxxxxxxxxx>
- Date: Wed, 10 Nov 2010 17:25:40 +0000
Hi, Ranjith,
mDDR DRAM parts with 200 MHz clock can have rise time as fast as ~200ps, so
2-inch trace will exhibit Txline effect. In addition, please consider mDDR does
not have ODT and rely on Txline Z0 matching driver's source impedance. So you'd
expect close to full reflection at the receiver side. This present overshoot
and increases xtalk. You want to check through simulation or measurement that
the waveshape at receiver side still meet JDEC spec for timing as well as
voltage spec with sufficient margin( especially overshoot spec). On EMC side,
this noise consists of harmonics of 200 MHz will need to find a sizable antenna
to cause RE failure. It is relatively easy to mitigate by either avoid the
noise coupling to an antenna structure ( cable/metal plate, etc), or filter
cables whose signal might pick up noise from mDDR block.
Hope it helps!
Catherine Xu
__________________________________
Lead HW Design Engineer, Ph.D
HP ICS CHIL - San Diego
__________________________________
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of steve weir
Sent: Wednesday, November 10, 2010 7:00 AM
To: Embedded
Cc: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: mDDR (200MHz) without Series Termination
The best thing to do is run a simulation that includes models for the
parts that you are using. If you do not have simulation capability,
then at least look at the rise and fall times in the models to estimate
your situation.
Steve.
Embedded wrote:
> Dear Experts,
> We are using TI AM37x processor with mDDR interface in our design.
>
> The mDDR maximum clock frequency is 200MHz.
>
> In our PCB Layout, we are placing mDDR chip close to AM37x CPU
> and the maximum trace lenghth between mDDR and CPU is less than 2 inch
> (Approximately 1.8 inch) only.
>
> In this case, do we need provide series termination (trace length less than 2
> inch only)?
>
> Will there be any EMI issues if we are not using series termination?
>
> Looking forward your response. Thanks in Adavnce.
>
> Thanks and Regards
> Ranjith
>
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--
Steve Weir
IPBLOX, LLC
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