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

  • From: Scott McMorrow <scott@xxxxxxxxxxxxx>
  • To: ckumar@xxxxxxxxxxx
  • Date: Thu, 8 Mar 2012 13:54:38 -0500

I strongly agree with Kumar.  Input/output capacitance, ESD structures, and
analog wave shaping filters all appear before the receiver or after the
driver, on the channel side.  They modify the return loss of the device,
and are therefore not isolated from the channel.  These need to be part of
the pure analog model.

Any wave shaping that occurs that is essentially isolated from the channel,
such as, pre-driver filtering, natural amplifier rolloff, etc, can be
incorporated into the algorithmic portion of the model.

If the non-isolated analog portions of the model are correct, and return
loss measurements of the device and model match, then, and only then, can
the algorithmic filter be tuned to match the final input/output response of
the circuit.



On Thu, Mar 8, 2012 at 1:41 PM, ckumar <ckumar@xxxxxxxxxxx> wrote:

> It depends on whether you have parasitics at your tx output. If there are
> (like the esd caps) they should be in the circuit. If you put them inside
> the ami model you will simply miss the interaction (reflections) between
> the parasitics and the pkg/pcb channel.
>
> if you have the circuit models you can test it with two different of the
> ami model and compare it against circuit simulation for different channels
>
> On Thu, 8 Mar 2012 10:15:05 -0800, David Banas <DBanas@xxxxxxxxxx> wrote:
> > 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
> >
> > Did you know Altera offers over 150 free online technical training
> >
> courses<
> http://www.altera.com/servlets/searchcourse?coursetype=Online&WT.mc_id=t9_ot_mi_mi_tx_a_311
> >?
> > Take one today!
> >
> >
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Scott McMorrow
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