[ibis-macro] Re: clock_times .... yet again
- From: "Dmitriev-Zdorov, Vladimir" <vladimir_dmitriev-zdorov@xxxxxxxxxx>
- To: "Mike Steinberger" <msteinb@xxxxxxxxxx>
- Date: Wed, 14 Apr 2010 14:06:25 -0600
Mike,
> I question the practical relevance of your concern about missing or
duplicated waveform points at the edge of an eye diagram.
Perhaps the brief answer is that superimposing disconnected or
overlapped waveform pieces may cause distortions of the jitter PDF that
accumulates at eye edges. I'm not ready to discuss the numbers but the
approach does not seem technically clean. In particular, it cannot
correctly account for peak to peak jitter.
Vladimir
-----Original Message-----
From: Mike Steinberger [mailto:msteinb@xxxxxxxxxx]
Sent: Wednesday, April 14, 2010 1:51 PM
To: Dmitriev-Zdorov, Vladimir
Cc: fangyi_rao@xxxxxxxxxxx; scott@xxxxxxxxxxxxx;
ibis-macro@xxxxxxxxxxxxx
Subject: Re: [ibis-macro] Re: clock_times .... yet again
Vladimir-
The short answer is that your second statement is correct and always has
been
> "the standard way of building the eye histogram from Rx output is not
> defined in details and could be implementation specific"
I question the practical relevance of your concern about missing or
duplicated waveform points at the edge of an eye diagram. It is
certainly mathematically possible that there could be missing or
duplicated waveform samples at the edge of an eye diagram. When this
happens, how will it affect the results of the analysis? And if it
doesn't affect the results of the analysis, is it worth discussing?
Mike S.
Dmitriev-Zdorov, Vladimir wrote:
> Mike,
>
> We are talking about different things. My point was that the spec
should
> be definite enough about what is a correct meaning and usage of clock
> times.
> You are saying that since you do a specific type of simulation
> successfully, there is no reason to worry about the accurate
definition.
> Or did I take it wrong?
>
> Any abstract EDA tool gets a long waveform and clock times output from
> Rx DLL. This is to be used to create eye "histograms". Do we need to
> formally define the standard way of doing this or remain silent on
this
> point thus leaving the possibility that the result is implementation
> dependent?
>
> The best I can figure out from the spec and our discussion so far is
> this:
>
> "EDA tool will use the portion of the waveform from tick_time_N to
> (tick_time_N+1UI) to fill the eye histogram. It is allowed that some
> portions of the Rx output waveform will be duplicated or missed in the
> histogram if the clock times are non equidistant"
>
> or
>
> "the standard way of building the eye histogram from Rx output is not
> defined in details and could be implementation specific"
>
>
> Vladimir
>
> -----Original Message-----
> From: Mike Steinberger [mailto:msteinb@xxxxxxxxxx]
> Sent: Wednesday, April 14, 2010 11:35 AM
> To: Dmitriev-Zdorov, Vladimir
> Cc: fangyi_rao@xxxxxxxxxxx; scott@xxxxxxxxxxxxx;
> ibis-macro@xxxxxxxxxxxxx
> Subject: Re: [ibis-macro] Re: clock_times .... yet again
>
> Vladimir-
>
> If you want to worry about missing or duplicated data, you might want
to
>
> consider the case of an odd/even receiver architecture. As you well
> know, the IBIS AMI API is based on the assumption that there is a
single
>
> data path, and yet we routinely and successfully use IBIS AMI to model
> receivers that have two or four data paths. In such cases, the
waveform
> in each data interval is the waveform at the decision circuit whose
> decision is actually going to be used for that data bit. Thus, the
> receiver model output waveform and the resulting eye diagram is built
up
>
> from segments of waveform that come from different parts of the
circuit
> altogether.
>
> This all reproduces measured data quite well, so long as the switch in
> waveform segments always occurs at the edge of the eye.
>
> Mike S.
>
> Dmitriev-Zdorov, Vladimir wrote:
>
>> But here is a minor technical problem: if you do this way, and the
>> clock times are not equidistant, then some portions of the waveform
in
>>
>
>
>> your histogram are counted twice and some could be missing. This is
>> another Pandora box: what's a definition of an eye histogram built
>> from waveform and non-equidistant clock times?
>>
>> Vladimir
>>
>>
>
>
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