[SI-LIST] Re: DDR2 eye-diagram masks creation
- From: Hermann Ruckerbauer <Hermann.Ruckerbauer@xxxxxxxxxxxxx>
- To: weirsi@xxxxxxxxxx
- Date: Tue, 09 Oct 2012 12:59:38 +0200
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
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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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