[SI-LIST] Re: How to estimating signal waveforms at inaccessible points in DDR3 or 4?
- From: Hermann Ruckerbauer <Hermann.Ruckerbauer@xxxxxxxxxxxxx>
- To: luliu@xxxxxxxxxx, "si-list@xxxxxxxxxxxxx" <si-list@xxxxxxxxxxxxx>
- Date: Fri, 23 Jan 2015 18:23:39 +0100
Hello,
In addition to getting the passive models for embedding the multipoint
and variable termination of the DDR memory bus is causing big problems.
So even if you have the models ot the channel your run into the issue,
that you need to know which termination settings are applied to use
tools like infiniisim.
So you need exactly to know the termination scheme for e. g. writes to
the given rank. To know this you might need to monitor ODT signals to
other ranks and also need to know dynamic termination.
One can build quite complex embedding structures with Infiniisim, but a
double slot memory system will bring also such a tools to the edge what
is possible.
You need also to know the Memory controller TX Ron and have a model of
the complete channel to do this correct.
And last but not least the separation between Write/Read and also Write
to the specific rank need to be decoded exactly.
And your scope application might take for overshoots the complete trace
and not only the write bursts, but for read bursts the De-Embedding
setup is not correct.
So even if you do have the models available it is a really tricky task
to implement the setup for the embedding correctly.
Question is how accurate you want/need to be .. often i work with the
very simplified setup that I measure after the serial termination on the
DIMM and just embedd the rest of the routing on the DIMM (and assume
some specific termination scheme).
But I know that this is only a very rough estimation of the problem ...
Hermann
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Am 23.01.2015 um 10:06 schrieb Robbie Liu:
> Dear All:
>
> You may treat this question as a follow up discussion of recently hot
> discussion "tips of using TDR probe " and "Pin vs. Die", so I may thanks to
> those experts first ,for their wonderful knowledge sharing.
>
> The question will be met by many hardware engineers such that our
> DDR3/4 chip may be imaging mounted on board , or the board use HDI so you
> can't have test point close enough to the end.
>
> Take DDR write as example, If we just have a test point (TP1)10mm
> away from the DDR3 chip, and you want to estimate the signal waveform at the
> DDR3 die (TP2 ), we need to know the S21 from TP1 to TP2, but for most of
> us didn't have such capability to access the TP2, so the problem comes.
>
> Certainly you can use 2D or 3D EM tool to get the channel S
> parameter, but the high accuracy need experience , and the package file is
> difficult to get.
>
> So can we just use one port test from TP1 ,to get the S parameter of
> this two port network?
>
>
> We notice two papers recently mentioned this topic , one is by
> Tomohiro Kinoshita, Shoichi Hara, Eiji Takahashi ,Panasonic, A technique for
> estimating signal waveforms at inaccessible points in high speed digital
> circuits, 2013 9th International Workshop on Electromagnetic Compatibility of
> Integrated Circuits (EMC Compo), December 15-18, Nara. Japan, it use their
> own Novel Electromagnetic Tool 'MomCACE' to get the ABCD matrix from TP1 to
> TP2, then estimate the waveform at the channel end.
> Another is by Evelyn Mintarno#1, Steven Ji*2 , A Practical Method to
> Characterize Interconnect in a Fully Loaded System, and its Application to
> DDR3 Channel, Proceedings of the 38th European Microwave Conference, , based
> on my understand (maybe wrong ), the method is use for characterize the
> channel between the CPU and the SO DIMM connector, right? I was wondering if
> we can push it further , like the PCB +Package, so that we can use the s
> parameter to estimate signal waveforms at inaccessible points in high speed
> digital circuits, for example , the imaging mounted DDR3 chip on board. The
> condition at port 2 may change between ODT 40, ODT 75 and ODT120, or ODT
> OFF, not sure if it is possible.
> What is your opinions ? do you have better solutions?
>
>
>
>
> Thanks and Regards,
> LIU Luping
>
>
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