[SI-LIST] Re: mDDR (200MHz) without Series Termination

  • From: Aneesh G <aneesh.govindan@xxxxxxxxx>
  • To: hw_si@xxxxxxxxxxxxxx
  • Date: Thu, 11 Nov 2010 11:33:39 +0530

Hi Ranjith,
     Eventhough the length is approx 1.8 Inch there are chances for
overshoot,ringing  and undershoot. Therefore its always better to go for
simulation. Incase if series terminations are required pl try with inbuilt
ODT.
Regards,

Aneesh G
On Thu, Nov 11, 2010 at 2:32 AM, Hermann Ruckerbauer <
hermann.ruckerbauer@xxxxxxxxxxxxx> wrote:

> Hello,
> as Cathereine already mentioned:
> There is a very high possiblitly that you will get problems with
> overshoots when working without serial termination.
> For DQ signals (writes) and CA signals you need to take a close look on
> the available drivestrength settings on the TI controller, and even not
> checking the datasheet I would guess you have a problem in violating the
> JEDEC overshoot spec without a serial termination!
> For the Reads you also need to check the Controller overshoot specs, but
> I guess you are in a similar situation there.
>
>
> A simulation of this setup to get a fast indication is done quite fast
> and should not really require a lot of effort. As X-talk can be really
> high on such an unterminated bus I would do at least a 5 coupled line
> simulation (3 coupled lines only if you have quite large spacing between
> the lines).
>
> Best Regards
>
> Hermann
>
>
>
>
>
> EKH - EyeKnowHow
> Hermann Ruckerbauer
> www.EyeKnowHow.de <http://www.eyeknowhow.de/>
> Hermann.Ruckerbauer@xxxxxxxxxxxxx
> Veilchenstrasse 1
> 94554 Moos
> Tel.:   +49 (0)9938 / 902 083
> Mobile: +49 (0)176  / 787 787 77
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>
> schrieb Xu, Catherine (ICS):
>  > 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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-- 
Warm Regards
Aneesh G

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