[SI-LIST] Re: DDR2 eye-diagram masks creation
- From: steve weir <weirsi@xxxxxxxxxx>
- To: Hermann Ruckerbauer <Hermann.Ruckerbauer@xxxxxxxxxxxxx>
- Date: Tue, 09 Oct 2012 06:46:12 -0700
Hermann, the need for multiple qualification masks does not alter the
either the reality or the utility of the eye. If for example the eye is
narrower than tDPIW one immediately knows that they have a problem.
TSimilarly, Tsu, and Th masks will determine if those parameters have
been met. In all cases the geometry gives a clear view of margins,
positive or negative and clues as to what the major impairments are.
Best Regards,
Steve.
On 10/9/2012 3:59 AM, Hermann Ruckerbauer wrote:
> Hello Steve,
>
> I did not say, that an eye can not be drawn. I think the question was to
> generate a Mask and for memory up to DDR3 this is not possible (guess
> DDR4 changes this one):
>
> One can not take the setup/hold times and generate an eye mask with the
> AC/DC levels.
> It is not allowed to apply tDS(min) and tDH(min) at the same time,
> because this would violate tDIPW (data input pulse width).
> Or if you take tDS(min) and draw t_VAC for special speed grades the
> resulting "eye mask" is much larger as just tDS + tDH.
> So there are several timings that need to fulfilled at the same time and
> it is not possible to combine this in a single mask.
> In the video on my website the case with t_VAC is shown.
>
> As you mentioned one need to take care HOW the eye is generated. In the
> Source Sync system it is required to take the timing reference (so for
> DQ the DQS rising and falling), place this in the center and draw the
> corresponding DQ edges (before and after) around. This needs to be done
> for each DQS edge. I know that scopes can do this in the meantime .. I'm
> not sure how many simulators are able to evaluate an eye this way ..
>
> Even I know it is not correct: My standard Eye evaluation is an AC/DC
> based eye opening.
> Based on this I can calculate Timing budgets (accounting for DQS jitter).
>
> Maybe this is some discrepancy in wording: An eye Mask defines an area
> the signal is not allowed to cross. The AC/DC open Data window
> evaluation is NOT an eye mask even it looks somehow like this.
>
> Hermann
>
>
>
> Our next Events:
> ================
>
> "Open the Black Box of Memory"
> Seminar on 08/09. November 2012
>
> Check our website or contact us for details
>
> EKH - EyeKnowHow
> Hermann Ruckerbauer
> www.EyeKnowHow.de
> Hermann.Ruckerbauer@xxxxxxxxxxxxx
> Veilchenstrasse 1
> 94554 Moos
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>
> schrieb steve weir:
>> Hermann, I disagree a bit here. Source synchronous busses have timing
>> eyes just like channels with embedded clocks. Eye diagram captures for
>> source synchronous busses should trigger on the timing strobe. Levels
>> need to satisfy the AC signal thresholds. Measuring the eye is a little
>> bit of a PITA because timing is against both clock edges. One way
>> around that is to perform separate captures on each clock edge.
>>
>> Steve
>> On 10/9/2012 12:40 AM, Hermann Ruckerbauer wrote:
>>> Hello,
>>>
>>> there is no real eye mask for DDR2/DDR3. On can generate some AC/DC
>>> based eye opening, but this is not correct as DRAMs do have a source
>>> snyc edge by edge specification instead of an eye mask.
>>> Some time ago I generated a movie/presentation that you can download on
>>> my website.
>>>
>>> Go to www.EyeKnowHow.de
>>> under Download/Movies you will find a DDR3_SetupHold_tutorial at the
>>> bottom. This was done for DDR3, but is basically valid for DDR2 as well..
>>>
>>> For anybody how is interested there in more detail: just visit our
>>> Seminar (see below) ;-)
>>>
>>>
>>> Hermann
>>>
>>> Our next Events:
>>> ================
>>>
>>> "Open the Black Box of Memory"
>>> Seminar on 08/09. November 2012
>>>
>>> Check our website or contact us for details
>>>
>>> EKH - EyeKnowHow
>>> Hermann Ruckerbauer
>>> www.EyeKnowHow.de
>>> Hermann.Ruckerbauer@xxxxxxxxxxxxx
>>> Veilchenstrasse 1
>>> 94554 Moos
>>> Tel.: +49 (0)9938 / 902 083
>>> Mobile: +49 (0)176 / 787 787 77
>>> Fax: +49 (0)3212 / 121 9008
>>>
>>> schrieb danko miocinovic:
>>>> Dear Experts,
>>>> I am doing some verification of LPDDR2 memories and my question is about
>>>> creating eye-diagrams. I got some material from Agilent but it gives not
>>>> enough details.
>>>> How do you create eye-diagram mask, what are the boundaries? If we imagine
>>>> the central romboid of a mask, I am interested if there is some detailed
>>>> tutorial about setting those boundaries.
>>>> If I have e.g. 533 memory and I know exactly what the frequency is, I can
>>>> calculate the UI x-size and easily create it.
>>>> What are boundaries for Y coordinates in this central part (grayed-out
>>>> area), how to create them? Do I put some minimal or maximal values there
>>>> (maximum values sound as the worst case)?
>>>>
>>>> I hope I was clear enough about what I would like to know, if not I could
>>>> provide more info.
>>>>
>>>> Thank you.
>>>>
>>>>
>>>>
>>>> Kind regards,
>>>>
>>>> Danko Miocinovic
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