[ibis-macro] Re: Question on dividing up the Tx behavior between the AMI and analog portions of the model

  • From: "Muranyi, Arpad" <Arpad_Muranyi@xxxxxxxxxx>
  • To: James Zhou <james.zhou@xxxxxxxxxx>, 'IBIS-ATM' <ibis-macro@xxxxxxxxxxxxx>
  • Date: Tue, 13 Mar 2012 00:17:04 +0000

James,

I think both David and Terry were putting their
analog data into their S-parameter block that
followed their legacy IBIS model, but in order
to drive that analog model with an ideal step
function they had to make the [Ramp] or V-t
table as steep as possible.

Such text doesn't exist in the specification yet,
because this is all evolving now as we speak.
The analog BIRDs are currently discussed in the
ATM meetings and we do not have the final results
of what will go into the specification yet.

Thanks,

Arpad
=====================================================

From: James Zhou [mailto:james.zhou@xxxxxxxxxx]
Sent: Monday, March 12, 2012 7:11 PM
To: Muranyi, Arpad; 'IBIS-ATM'
Subject: RE: Question on dividing up the Tx behavior between the AMI and analog 
portions of the model

Hi Arpad,

David used "V-T curves of the analog IBIS model" and Terry "setting my ramp 
with extremely high dv/dt". These statements suggest that  (a) David put his 
analog data in [Rising/Falling Waveform] keyword and (b) Terry put his analog 
data in [Ramp] keyword.

If that is true, and these data are given to an EDA tool, my question is how is 
the EDA tool supposed to connect the AMI output to the analog input? I don't 
see any text in IBIS Specification 5.0 or BIRDs that address this issue. (That 
is, when the analog part is represented by [Ramp] or [Rising/falling 
Waveform]). Please let me know if such text exist.

Regards,
James


From: ibis-macro-bounce@xxxxxxxxxxxxx<mailto:ibis-macro-bounce@xxxxxxxxxxxxx> 
[mailto:ibis-macro-bounce@xxxxxxxxxxxxx]<mailto:[mailto:ibis-macro-bounce@xxxxxxxxxxxxx]>
 On Behalf Of Muranyi, Arpad
Sent: Monday, March 12, 2012 4:51 PM
To: 'IBIS-ATM'
Subject: [ibis-macro] Re: Question on dividing up the Tx behavior between the 
AMI and analog portions of the model

James,

As far as I can tell, the digital input signal (stimulus) you mentioned
has nothing to do with what David and Terry are talking about.  That
digital signal is purely an indication for the analog signal (whether
it is governed by [Ramp] or the V-t tables, doesn't matter) to begin
its course.  This is basically t=0 for the transition.

The transition amplitude and slope is defined by the reference
voltages of the I-V tables and [Ramp] or V-t tables.  This is
all analog.

There are models out there which try to make this "model" as
ideal as possible, giving it really fast edge rates and very
strong I-V current relationships, so that the block that follows
could be used for "wave shaping" and "impedance definition".  I
like to call this approach as the "Glorified Thevenin" model, in
which the IBIS analog model acts as the ideal source and the next
block (often times an S-parameter model) is the Thevenin impedance.

But I don't see any relationship in this and the "digital" stimulus
that goes into the legacy IBIS models.

Thanks,

Arpad
=====================================================================

From: ibis-macro-bounce@xxxxxxxxxxxxx<mailto:ibis-macro-bounce@xxxxxxxxxxxxx> 
[mailto:ibis-macro-bounce@xxxxxxxxxxxxx]<mailto:[mailto:ibis-macro-bounce@xxxxxxxxxxxxx]>
 On Behalf Of James Zhou
Sent: Monday, March 12, 2012 4:11 PM
To: Terry.Chen@xxxxxxxxxx<mailto:Terry.Chen@xxxxxxxxxx>; 
DBanas@xxxxxxxxxx<mailto:DBanas@xxxxxxxxxx>; 'IBIS-ATM'
Subject: [ibis-macro] Re: Question on dividing up the Tx behavior between the 
AMI and analog portions of the model

Hi David and Terry,

Both of your emails mentioned "analog IBIS model" and "IBIS-analog portion" 
represented by [Ramp] and/or [Rising/Falling Waveform] keywords in IBIS file.  
However, these "analog" IBIS models only take digital input signals,  as stated 
in IBIS Specification 5.0, page 71-72 and section 6b. The output of the 
"analog" IBIS model is not capable of tracking the amplitude changes in the 
input (other than a rise/fall transition). It would not make sense to feed the 
Tx AMI output to such digital inputs based on IBIS Specification 5.0.

If this approach of using [Ramp] and/or [Rising/falling Waveform] keywords to 
represent "analog IBIS model" is adopted by IBIS AMI flow, some clarification 
is needed on how to interpret and implement it.

Regards,
James Zhou
QLogic Corp.


From: ibis-macro-bounce@xxxxxxxxxxxxx<mailto:ibis-macro-bounce@xxxxxxxxxxxxx> 
[mailto:ibis-macro-bounce@xxxxxxxxxxxxx]<mailto:[mailto:ibis-macro-bounce@xxxxxxxxxxxxx]>
 On Behalf Of Chen, Terry
Sent: Thursday, March 08, 2012 10:33 AM
To: DBanas@xxxxxxxxxx<mailto:DBanas@xxxxxxxxxx>; 'IBIS-ATM'
Subject: [ibis-macro] Re: Question on dividing up the Tx behavior between the 
AMI and analog portions of the model

Hi David,

Actually I am interested in other's response to this question as well...

But, for the TX Driver I am currently modeling, I am doing exactly what you 
have prescribed and using the IBIS-analog portion as effectively an ideal step 
function (by setting my ramp with extremely high rise/fall dv/dt) and letting 
the step response filter inside my AMI model to shape my output waveform. Now, 
I am not sure if this is the "right" or "ideal" way to do it, but I am getting 
a reasonably good correlation in my Re-driver model with the actual lab 
measurements (the max jitter mismatch is < 8ps).

I hope this is at least an useful data point for you.

Regards,
Terry

From: ibis-macro-bounce@xxxxxxxxxxxxx<mailto:ibis-macro-bounce@xxxxxxxxxxxxx> 
[mailto:ibis-macro-bounce@xxxxxxxxxxxxx]<mailto:[mailto:ibis-macro-bounce@xxxxxxxxxxxxx]>
 On Behalf Of David Banas
Sent: Thursday, March 08, 2012 1:15 PM
To: 'IBIS-ATM'
Subject: [ibis-macro] Question on dividing up the Tx behavior between the AMI 
and analog portions of the model

Hi all,

Is it customary to split up the Tx behavior, such that the FFE is modeled in 
the AMI model and the pulse shaper in the analog model?
Or, is there a different dividing line that has been identified as "best 
practice".
(Or, am I completely off in the weeds?)

The context for this question: I just managed to get good correlation between 
our latest Tx AMI model and the HSPICE model.
And then I realized that, having dumped all of the behavior into the AMI model, 
I would need to put an ideal step function into the V-T curves of the analog 
IBIS model. And I wasn't sure that would be a good idea. (I'm guessing that 
that would reek havoc in most simulators; is that correct?)

Thanks,

David Banas
Sr. Member Technical Staff
Altera<http://www.altera.com/>
+1-408-544-7667 - desk

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