[SI-LIST] Re: DDR3 - AC parameter
- From: Christopher White <chris_k_white@xxxxxxxxxxx>
- To: "Katkoria, Deepak" <Katkoria.Deepak@xxxxxxxxxxx>, "si-list@xxxxxxxxxxxxx" <si-list@xxxxxxxxxxxxx>
- Date: Wed, 4 Aug 2010 09:14:03 -0500
Hi Deepak,
For question:
1. Vih(ac) is VREF (VDD/2) plus 150mV or 175mV depend on your part's speed
and whether you are referring to a DQ/DQS or an ADD/CMD line.
2. What do you mean by "less immune"?
3. VTT has the ADD/CMD terminated to it. Is it a buried plane in your
stack-up? Is it decoupled to VDD and/or GND?
4. AC175 is the VREF+175mV requirement for Vih(ac) and AC150 is the
VREF+150mV requirement for Vih(ac). Which one you use depends on your clock
rate and signal. From 1333 and up the DQ lines only support AC150.
5.
6. The AC ratings are primarily to ensure sufficient line levels before the
strobe arrives (setup time). The DC ratings still are used in the hold time
measurement.
*Christopher White*
Senior Engineer
SPPDG
Phone: 507-538-5606
Fax: 507-284-9171
E-mail: white.christopher1@xxxxxxxx
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On Wed, Aug 4, 2010 at 8:44 AM, bala <balaseven@xxxxxxxxx> wrote:
> Hi Deepak,
> good day,
>
> 2.ADD/CMD need extra care. Hope u meant fly by termination.
> 3.Use separate plane for processor and memory.Dont use same plane for both
> device and follow some EMC guidelines.
>
>
>
> On Wed, Aug 4, 2010 at 2:26 PM, Katkoria, Deepak <
> Katkoria.Deepak@xxxxxxxxxxx> wrote:
>
> > Halo,
> > Presently, I am working on DDR3 interface.
> > I would like to know following things,(which are not explain in Std.)
> > 1. how to check the AC input logic high Vih(ac) in Oscilloscope??
> >
> > 2. For the Fly by architecture, which signal is less immune and need
> > extra care for routing on inner layer DQ or ADD/CMD
> >
> > 3. I am getting lots of EMC emission on VTT plan for on board DDR3.
> What
> > could be the reason?
> >
> > 4. Do you know the difference between AC175 and AC150??
> >
> > 5. Why there is AC reading in high speed signals, upto know I have
> only
> > dealt with Vih(dc) and never used Vih(ac).
> >
> > 6. why are they using AC rating with DC ratings??
> >
> >
> > Cheers,
> > Deepak
> >
> >
> >
> >
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> --
> bala
>
>
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