[ibis-macro] Re: clock_times .... yet again
- From: "Todd Westerhoff" <twesterh@xxxxxxxxxx>
- To: "'Scott McMorrow'" <scott@xxxxxxxxxxxxx>
- Date: Wed, 14 Apr 2010 17:38:19 -0400 (EDT)
Okay, so how much difference will this make to the simulation results
based on the waveform overlapping Vladimir was concerned about?
Todd.
________________________
Todd Westerhoff
VP, Software Products
SiSoft
6 Clock Tower Place, Suite 250
Maynard, MA 01754
(978) 461-0449 x24
twesterh@xxxxxxxxxx
www.sisoft.com
_____
From: Scott McMorrow [mailto:scott@xxxxxxxxxxxxx]
Sent: Wednesday, April 14, 2010 5:20 PM
To: Todd Westerhoff
Cc: vladimir_dmitriev-zdorov@xxxxxxxxxx; 'Mike Steinberger';
fangyi_rao@xxxxxxxxxxx; ibis-macro@xxxxxxxxxxxxx
Subject: Re: [ibis-macro] Re: clock_times .... yet again
Todd,
pk-pk jitter for good CDRs is designed to be around +/- 0.05 UI at a 10-12
confidence interval. Deterministic jitter transfer and multiplication in
the CDR loop will be added on top of this. CDR jitter can easily approach
+/- 0.1 UI at a 10-12 confidence interval under stress testing.
+/-10% is a reasonable number. Shortest period is 0.9 UI. Longest period
is 1.1 UI.
Scott
Todd Westerhoff wrote:
Vladimir,
What is the magnitude of the effect you're talking about?
Todd.
________________________
Todd Westerhoff
VP, Software Products
SiSoft
6 Clock Tower Place, Suite 250
Maynard, MA 01754
(978) 461-0449 x24
twesterh@xxxxxxxxxx
www.sisoft.com
-----Original Message-----
From: ibis-macro-bounce@xxxxxxxxxxxxx
[mailto:ibis-macro-bounce@xxxxxxxxxxxxx] On Behalf Of Dmitriev-Zdorov,
Vladimir
Sent: Wednesday, April 14, 2010 4:06 PM
To: Mike Steinberger
Cc: fangyi_rao@xxxxxxxxxxx; scott@xxxxxxxxxxxxx; ibis-macro@xxxxxxxxxxxxx
Subject: [ibis-macro] Re: clock_times .... yet again
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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