[uunet!cadence.com!cpk: Re: Re[2]: IBIS Open Forum 1/6/95 Meeting Minutes]

The VI curves are a DC measurement and so only a DC load would be a usefull
comparison point. That means a Thevinin Equivalent R and V. Capacitor charge time
or Transmission line behavior are extractable from this data but are not part of the
IV curve. Of course, given an IV curve and DC load conditions, the correct answer is
calculable by hand and not very interesting.

a better question is "is calculable a word?"

jonp

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Date: Tue, 17 Jan 95 14:04:03 -0500
From: uunet!cadence.com!cpk (C. Kumar)
To: uunet!vhdl.org!ibis, uunet!ccm.fm.intel.com!Arpad_Muranyi
Subject: Re: Re[2]: IBIS Open Forum 1/6/95 Meeting Minutes

By standard load, I waa trying to indicate the following.

The ac v-t specifications include loads under whcih the measurements were taken.
So if the siumulations reproduce the v-t behavior at those load conditions then
they are self verifying and are pracically meaningful.

For a practically meaningful v-i verification, we have to drive a reference load with the
device and then compare the resulting v-t with some reference waveform. What is a useful refernce load. Is it daisy chain transmission line with ten loads? Or is it a simple capacitor? In the past we have been unable to come to agreement on identifying both the reference load and waveforms.

This is what I meant by refernce loads for v-i verification.
>
> Kumar,
>
> I am still not sure what you mean by "standard load". When you do a voltage
> sweep on a device, you are forcing the voltage while you are measuring the
> current. When yo do this sweep, you are actually "loading" the device with the
> voltage source. You can look at that voltage source as an ideal, 0 Ohm source
> or as a Thevenin combination of an ideal source with a series resistor. Either
> way, you are sweeping between a certain voltage range at the output of the
> device to get an I-V curve, regardless of what R is in your Thevenin circuit.
> Your I-V curve will be the same whether R in the Thevenin circuit is small or
> large. You will just have to increase the sweep range of the voltage source
> inside the Thevenin circuit for larger R values to get the same sweep range at
> the pin of the device.
>
> What is the probelem? Am I missing something obvious?
>
> Arpad
>
> ------------------------------------------------------------------------------
>
> The problem with I-V checking is that there is no "standard" load as
> with V-T curves. We already went through this i-v standard load discussion
> and dropped it because
> of controvorsey. The reason I raised it because that I think that in
> signal integrity situations the dc I-V characteristic has more has a dominant
> effect on the resulting waveforms and we have no reference to check against.
>
> >
> > Hello IBIS gurus,
> >
> > In the last minutes Kumar suggested DC checking (see quote below). I am not
> > sure what he means, but just as we can use V-T tables for AC checking,
> couldn't
> > the I-V curves be used for DC checking?
> >
> > Arpad
> > Intel Corporation
> >
> >
> > > Compliance
> > > Will pointed out that the V/T table can be used to as a type of compliance
> > > test/sanity check. Kumar would like to see a DC check as well.
> >
> > > AR Kumar: Post an EGG for DC checking.
> >
> >
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> Subject: Re: IBIS Open Forum 1/6/95 Meeting Minutes
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> From: cpk@cadence.com (C. Kumar)
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Received on Tue Jan 17 14:49:55 1995