FreeLists / si-list / [SI-LIST] Re: Ccomp in HSPICE

["Jeremy Plunkett" <jeremy@xxxxxxxxxxxxxxx>]

Tim,
If the buffer has a reasonably high drive strength (and many do, =
regardless of their specifications), then you will not see much =
difference in the output waveform for small changes in buffer =
capacitance, since the RC constant of the output impedance and buffer =
capacitance is high compared to the edge rate.  However for the versions =
of Hspice that I've tested this with, I've always have seen a =
difference.  Try creating versions of the model with 0pF and 100pF for =
C_comp, and run them in the same simulation into the same test load and =
compare the waveforms.  Any test load will work, but long T-lines or =
resistive terminations may show it more clearly since the edge rate will =
be faster than with a capacitive load.

regards,
Jeremy




Jeremy Plunkett
Signal Integrity Engineer
ServerWorks Corp
www.serverworks.com




-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Luca Giacotto
Sent: Tuesday, May 07, 2002 6:06 PM
To: SI-List
Subject: [SI-LIST] Re: Ccomp in HSPICE



Hello Tim!

You may try to simulate the B-model attached to a long line (e.g. =
TD=3D3D5ns).
Put a big resistance at the end of the line (e.g. 1Gohm).
In this experiment, you should see that the incident waveform is
independent from Ccomp, while the reflections at the driver side
strongly depends on it.

Hope this helps,
Luca



On Tue, 7 May 2002 14:25:21 -0400
"Timothy Coyle" <Timothy.Coyle@xxxxxxx> wrote:

> Hi,
> I am trying to see the effects of different Ccomp values of an IBIS =
outpu=3D
t=3D20
> buffer in HSPICE.  When I change Ccomp and re-run simulations, I see =
no=3D
=3D20
> difference.=3D20
> I'm sure I'm leaving something out, so if anyone can shed some light =
on=3D
=3D20
> this it would be appreciated.=3D20
>=3D20
>=3D20
> Thanks in advance,
> Tim
>=3D20
>=3D20
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--=3D20
Luca Giacotto <lgiacott@xxxxxxxxx>

*****
Il modo pi=3DF9 sicuro di perdere una battaglia
=3DE8 di non combatterla.

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