[ibis-macro] Re: clock times
- From: Scott McMorrow <scott@xxxxxxxxxxxxx>
- To: Mike Steinberger <msteinb@xxxxxxxxxx>
- Date: Thu, 01 Apr 2010 19:30:25 -0400
Mike
Thank you for taking the time to answer. Sorry to be a bother. I have
another question. Based on this, we know what the EDA platform should
do. But, do we know what the DLL will provide? There are two choices:
A) clock_ticks truly represent the points where the CDR clock has
locked on the data transition. In this case our waveforms are
essentially differential crossing aligned, as the spec requires, but
we've lost any information regarding the sample point, and it is
impossible to determine where the sample point is.
B) clock_ticks represents the the sample point minus 1/2 the UI
period. In this case our waveforms are sample point aligned, and
all is right with the world.
If option A is chosen, I don't believe that sample jitter is properly
modeled. In both cases the eye is displayed correctly, since both are
based on the same clock, but the exact sample point is unknown.
regards,
Scott
Mike Steinberger wrote:
Scott-
We've been using your option A.
Mike S.
Scott McMorrow wrote:
All
We are looking at the specification for clock_times and have come
across the following problem with these two sentences:
The clock times are the times at which clock signal at the output
of the clock
| recovery loop crosses the logic threshold. It is to be assumed
that the
| input data signal is sampled at *exactly one half clock period*
after a
| clock time.
I really hate assumptions in specifications since they may be wrong,
and are up to interpretation. I believe that the spec really means
to define the internal sample point of the sampler, slicer, track
hold ... whatever, by having the EDA platform move the delivered
clock tick from the clock_times vector by 1/2 a clock period, or UI.
If that interpretation is correct then which of the two is correct?
1/2 a clock period is defined to be:
A) one half of the nominal UI
B) one half of the instantaneous UI between two clock samples
How is this currently being implemented in currently developed models?
regards,
Scott
--
Scott McMorrow
Teraspeed Consulting Group LLC
121 North River Drive
Narragansett, RI 02882
(401) 284-1827 Business
(401) 284-1840 Fax
http://www.teraspeed.com
Teraspeed® is the registered service mark of
Teraspeed Consulting Group LLC
--
Scott McMorrow
Teraspeed Consulting Group LLC
121 North River Drive
Narragansett, RI 02882
(401) 284-1827 Business
(401) 284-1840 Fax
http://www.teraspeed.com
Teraspeed® is the registered service mark of
Teraspeed Consulting Group LLC
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