Re: [IBIS-Users] How do simulators handle C_Comp?

From: Sanjay Mehta <sanjay.mehta_at_.....>
Date: Wed Mar 16 2005 - 18:42:37 PST
Thank you all for the response to my question.

- Sanjay

"Angulo, John" wrote:

> Sanjay,
>
> I'm sorry I failed to reply to this promptly.  To confirm statements
> implied, Hyperlynx avoids double counting C_comp when performing
> rise/fall simulations, just like ICX.  It is straightforward for the
> driver to supply the extra current necessary to charge the C_comp
> capacitance so that the simulation continues to reproduce V-t table
> waveforms when the buffer is driven into V-t table loads.
>
> Best regards,
>
> John Angulo
> Software Development Engineer
> Hyperlynx Products
> Mentor Graphics Corp.
>
> > -----Original Message-----
> > From: owner-ibis-users@eda.org
> > [mailto:owner-ibis-users@eda.org] On Behalf Of Abril,
> > Giovanni (Space Technology)
> > Sent: Wednesday, March 02, 2005 8:33 PM
> > To: Sanjay Mehta; ibis-users@eda.org
> > Cc: Muranyi, Arpad
> > Subject: RE: [IBIS-Users] How do simulators handle C_Comp?
> >
> > Sanjay,
> >
> > Here is a response to the same question from a few years ago,
> > with respect to the ICX simulator, also from Mentor:
> >
> > The effect of C_comp is only double counted if you are using
> > a substandard simulator.  All the major simulators that I
> > know of expect C_comp to be specified with the same (static
> > approximation) value as what is included in the waveforms.
> > Somewhere in the simulator this is reconciled.  Usually it is
> > done is such a way that the capacitive effect is calculated
> > out of the waveforms and then the lumped capacitor is present
> > at the pin during the transient simulation..
> >
> > As Arpad noted, the capacitive effect is usually impossible
> > to remove from the SPICE models used to derive IBIS data.  It
> > is part of the transistor models.  Arpad and others have
> > proposed methods of finding the best static value of the die
> > capacitance to use for C_comp and this value needs to be
> > there.  If you put the value of 0 for C_comp then the
> > simulator will try to back out the capacitance and put no
> > capacitance at the pin.  At first this seems OK because the
> > waveforms still have all the capacitive effect.  The problem
> > appears when a reflected signal hits this pin or if this pin
> > is hi-Z.  There would be no capacitive loading and you would
> > then have invalid simulations.
> >
> >
> > I assume Hyperlynx is not a "substandard simulator" so it
> > shouldn't double-count either.
> >
> >
> >
> > -----Original Message-----
> > From: owner-ibis-users@eda.org [mailto:owner-ibis-users@eda.org]On
> > Behalf Of Sanjay Mehta
> > Sent: Wednesday, March 02, 2005 11:36 AM
> > To: ibis-users@eda.org
> > Cc: Muranyi, Arpad
> > Subject: Re: [IBIS-Users] How do simulators handle C_Comp?
> >
> >
> > In practice, I would like to know how simulators such as
> > Hyperlynx account for this C_comp? Does it exclude
> > double-counting of the C_comp when performing rise/fall time
> > domain simulations?
> >
> > Can someone from the tool vendor answer this question?
> >
> > Thanks,
> >
> > Sanjay Mehta
> > Xilinx
> >
> > "Muranyi, Arpad" wrote:
> >
> > > Lee,
> > >
> > > The IBIS model's IV curve which determines its impedance does not
> > > include any C_comp effects.  The Vt curves which are used
> > to turn on
> > > and off the IV curves do include the C_comp effect in their
> > shape, but
> > > they do not effect the DC nature of the IV curves.  Therefore we do
> > > need to add a capacitor to account for the capacitive nature of the
> > > drivers (or receivers).  As stated in another response, this is
> > > necessary for getting the correct reflections in the
> > simulations when
> > > a wave hits the model.
> > >
> > > Arpad Muranyi
> > > Intel Corporation
> > > ------------------------------------------------------------
> > >
> > > -----Original Message-----
> > > From: owner-ibis-users@eda.org [mailto:owner-ibis-users@eda.org] On
> > > Behalf Of lee yang
> > > Sent: Tuesday, March 01, 2005 8:58 PM
> > > To: ibis-users@eda.org
> > > Subject: [IBIS-Users] C_Comp
> > >
> > > Hi,
> > > Since the C_Comp effect is already embedded in the Spice
> > model, hence,
> > > the generation of IBIS model automatically includes the
> > effect of it.
> > > I am wondering, since the C_Comp effect is already included in the
> > > IBIS model, why do we still need to put it in the IBIS
> > file? Why it is
> > > so important?
> > > Thanks a lot.
> > > -Lee
> > >
> > > _________________________________________________________________
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Received on Wed Mar 16 18:43:08 2005

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