[SI-LIST] Re: Ccomp in HSPICE
- From: "Mirmak, Michael" <michael.mirmak@xxxxxxxxx>
- To: "'jeremy@xxxxxxxxxxxxxxx'" <jeremy@xxxxxxxxxxxxxxx>,lgiacott@xxxxxxxxx, SI-List <si-list@xxxxxxxxxxxxx>
- Date: Wed, 8 May 2002 17:00:30 -0700
To amplify Luca's comments, c_comp changes in the IBIS model should not make
a difference to the driven waveform, at least on the initial edge.
For most tools, the c_comp effects are considered to be "baked into" the V-t
curves or ramp data for the driver; the actual c_comp value in the file is
ignored for the initial driving phase of the buffer (Innoveda tools, at
least in the past, were an exception). C_comp plays a role only when
reflections return to the driver or when the buffer receives.
In short, simulations into an ideal load where c_comp is being changed
within the IBIS model will not show any variations at all. Only if you
observe a reflective environment or a receiving buffer will c_comp
adjustment effects be apparent.
- Michael Mirmak, Intel Corp.
-----Original Message-----
From: Jeremy Plunkett [mailto:jeremy@xxxxxxxxxxxxxxx]
Sent: Tuesday, May 07, 2002 7:16 PM
To: lgiacott@xxxxxxxxx; SI-List
Subject: [SI-LIST] Re: Ccomp in HSPICE
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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