Subject: Re: [IBIS-Users] C-Comp
From: hazem@qualim.com
Date: Mon Jul 21 2003 - 02:40:39 PDT
Anshuli,
The v-t tables contain the c_comp behavior but at
certain loading conditions (50 Ohm to GND/VDD). We need
to tell the simulator the c_comp value in order to
update the internal differential equations with the
term c *di/dt at different loading conditions.
You can try this by setting C_comp to zero and try to
get the 50 Ohm to GND/VDD from the IBIS simulator. You
will get exactly the correct wave form versus SPICE.
Another trial is to set C_comp to zero and try to
simulate the buffer at 100 Ohm to VDD for example and
compare it with spice. You will get bad correlation
even with this simple load. On the other hand, if you
used the correct C_comp value you will get excellent
correlation even with very harsh loading conditions.
I also recommend to read this presentation as in the
first pages it demonstrate the importance of C_comp in
time response domain:
http://www.eda.org/pub/ibis/summits/jun02/hegazy.pdf
BR,
On Mon, 21 Jul 2003 14:49:29 +0530, Anshuli Goel wrote:
>
> Arpad
>
> As far as I understand the C_comp value is not taken
> into account for IV curve
> calculation , it is only added in the calculation in
VT
> curve , so while
> calculating VT curve we already have capacitance , why
> do we need to put
> C_Comp ??
>
> Anshuli
> "Muranyi, Arpad" wrote:
>
> > That is because the IV curves do not exhibit any
> capacitive
> > behavior, they are only DC. In order to put the
> capacitive
> > effects into the IBIS model we need to add a
> capacitance to
> > the IV curves.
> >
> > Arpad Muranyi
> > Intel Corporation
> >
>
===========================================================
> >
> > -----Original Message-----
> > From: Anshuli Goel [mailto:anshuli@ti.com]
> > Sent: Friday, July 18, 2003 6:16 AM
> > To: 'ibis-users@eda.org'
> > Subject: [IBIS-Users] C-Comp
> >
> > Hello Experts
> >
> > I have one naive question.
> > While defining the C_Comp we say "C_comp defines the
> silicon die
> > capacitance. This value should not include
> capacitance of
> > the package.The C_comp capacitance must represent
> what you see when you
> > look into the die at the die pad. This includes the
> die pad, metal
> > connections on the die, the driver transistor's
> capacitance, the receiver
> > (input)capacitance, everything that is on the die."
> >
> > But my understanding is that anyway the netlist is
> going to have driver
> > transistors in it in case of buffers, why do we need
> to account for the
> > capacitance for driver transistors ?? I can
> understand about the metal
> > connection and bond pad capacitance ,but I am not
> able to understand the
> > Transistors Capacitance part of it . Please clarify.
> >
> > Regards
> > Anshuli
> >
> >
>
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Hazem Hegazy
Tel: +20(2)4043350
Mobile: +20(10) 6052154
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