FreeLists / si-list / [SI-LIST] Re: Basic IBIS I/V curve question

[<marko.pulli@xxxxxxxxx>]

Hi Andrew and Gustavo,

Now I'm starting to see the truth.
I've learned from your responses that in IBIS models the I/V curves are =
only "pictures" of the output taken under a specific =
temp/voltage/process corner. So I guess editing the "picture" is making =
things even worse.

In my case the actual voltage is between 3.2V ... 3.4V.
In the IBIS model, however, the maximum curve is measured with 3.5V and =
min with 3.0V.
Simulation with min and max curves will give exaggerated results which =
means too much ringing or too slow edges. Well, I guess this is close =
enough result for IBIS only simulations.

Have you personally used different values in [Voltage range]?
Do you see any benefit in slightly adjusting the values in some cases to =
possibly get a "closer" estimate?

Br,
Marko


> -----Original Message-----
> From: ext Ingraham, Andrew [mailto:Andrew.Ingraham@xxxxxx]
> Sent: 07. November 2002 18:55
> To: Gustavo Blando
> Cc: si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Re: Basic IBIS I/V curve question
>=20
>=20
> > I am confused here. I though that even though the curves are VCC
> > relative on
> > IBIS
> > it does matter the voltage at which the VI curves where extracted.
> =20
> Yes it does.
>=20
> I wrote that the curves and supply voltage are independent, "ideally."
> In reality, the drive strength of real devices, as measured in a
> Vcc-relative way, does depend on the supply voltage.
>=20
> But IBIS is not detailed enough to show that dependency.  So when you
> use a model, you could use the minimum curve with something other than
> the minimum supply voltage.  The results ought to be conservative,
> because the real device would be slightly stronger/faster, at that
> supply voltage, than that dictated by the minimum I-V curve that the
> simulator uses.
>=20
> Some simulators (such as Hspice) let you choose the supply voltage
> separately from the I-V curve.  Others may make them linked=20
> so that you
> can't do that.
>=20
> Regards,
> Andy
>=20
>=20
>=20
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