Subject: RE: [IBIS-Users] C-Comp
From: Muranyi, Arpad (arpad.muranyi@intel.com)
Date: Mon Jul 21 2003 - 14:08:14 PDT
Anshuli,
The Vt curves include the effect of C_comp, but it needs to be
compensated out if there is an extra capacitance in the IBIS model
to account for C_comp. However, the C_comp capacitor must be
there so that when you look into the buffer you would see that
capacitance. The fact that the Vt curve has the effect of
C_comp does not mean that looking into the buffer you see that
capacitance, it only means that the curve is slower than it would
be without the capacitive effects.
In short, the C_comp is there to make the capacitive effects visible
to the rest of the circuit, but the compensation inside the buffer
is done to avoid double counting for it in the shape of the waveforms.
Arpad
======================================================================
-----Original Message-----
From: Anshuli Goel [mailto:anshuli@ti.com]
Sent: Monday, July 21, 2003 2:19 AM
To: Muranyi, Arpad; 'ibis-users@eda.org'
Subject: Re: [IBIS-Users] C-Comp
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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