Subject: Re: [IBIS-Users] Waveform mismatch question
From: Duane Mattheisen (duane.mattheisen@onsemi.com)
Date: Fri Jan 24 2003 - 13:29:34 PST
John
I was writing for a bench measurement not a simulation. The 50 ohms
is a common standard for the AC measurements. And if your on a AC bench
measuring of actual devices, a capacitor helps when put it on the power
supply side of the R_fixture not on the device side, what that does is
take any voltage drop out of the wires going from the power supply to
the R_fixture. For the DC measurement again on the bench the resistance
to make as low as possible is the fixture resistance which is between
the Voltage/Current measurement tool and the device.
On another note I down loaded s2ibis2_fix_tar.Z and s2ibis2_tar.Z but
did not know how to work with them. Is there any advice you can give me
to start?
Thanks Duane Matheisen
John Phillippe wrote:
>
> Duane Mattheisen wrote:
> > John Take out as much fixture resistance as possible in the DC
> > measurement.
> > Also for the AC measurement put a big capacitor (0.1uf and a >2.2uF
> > tantalum cap) to ground on the Rfixture having the other side of the
> > Rfixture that connects to the output as close as possible to the
> > output.
> > Sincerely Duane Mattheisen
> > "Angulo, John" wrote:
> >
> >>The following is posted on behalf of John Phillippe at Motorola. Please send any private replies to john.phillippe@motorola.com only.
> >>
> >>--------------------------------------------------
> >>
> >>Ibis Guru's,
> >> I get quite a few waveform mismatches between the rising/falling
> >>edges and the I/V curves like the one shown below.
> >>
> >>WARNING - Model pad_26v_fast: The [Falling Waveform]
> >> with [R_fixture]=50 Ohms and [V_fixture_max]=0V
> >> has MAX column DC endpoints of 0.05V and 1.75v, but
> >> an equivalent load applied to the model's I-V tables yields
> >> different voltages ( 0.16V and 1.91V),
> >> a difference of 6.66% and 8.94%, respectively.
> >>
> >>I'm curious if this is a common problem, or if there are some simple
> >>solutions to get everything to match up. I check the waveforms and set
> >>the sim time long enough to make sure the waveforms are stable. Any
> >>help/suggestions would be greatly appreciated.
>
> Duane,
> Since I'm using s2ibis2, I should make rload as small as possible?
> On the order of 1ohm? I read in this group before to use an rload of
> 50ohms since that is what most people are using, and that it is a bit of
> a "standard." I've also been told to have NO capacitance in the AC
> measurements, and again to only use a 50ohm resistor.
> I did try a run with a 0.1uF cap on the pad for the AC measurements,
> but that just slows the edge down.
>
> --
> John Phillippe
> SPS, 32 Bit Embedded Controller Division, IC Creation
> Motorola - 512-895-1835
> Austin, TX - john.phillippe@motorola.com
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