Subject: RE: [IBIS] IV curve question...
From: ruston, matt (ruston_matt@emc.com)
Date: Fri Nov 01 2002 - 12:23:58 PST
Ben, Tony:
Hi. I'm using Specctraquest.
The extraction process has left an "exaggerated" pwr_clamp and a weaker,
non-monotonic pulldown and pullup. When I translate the non-montonic
pulldown & pullup curves from Ibis to DML, the tranlator see's the
non-monotonic curve and does me a favor and flattens it out. Then, when you
add the exaggerated clamps (due to extraction) into the overall curve during
simulation, the clamping is stronger than it should be (by the difference
between the "real" bent curve, and the flattened DML curve).
The difference (in this case) can be 15 mA of extra clamping. It probably
won't hurt in the pulldown case since the inaccuracy is in the pwr_clamp
(tough to see that part of the curve being used when pulling low). But it
will hurt in the pullup case and in the high clamp of the receiver.
So, the simulator does it automagically, but it isn't the most accurate
representation. I just wanted to see the curves summed up BEFORE SQ "fixed"
them to see the true curves. They actually look reasonable, but won't be
used in the simulator that way.
Regards,
Matt
-----Original Message-----
From: Silva, Benjamin P [mailto:benjamin.p.silva@intel.com]
Sent: Friday, November 01, 2002 2:24 PM
To: ruston, matt; Ingraham, Andrew
Cc: ibis@eda.org
Subject: RE: [IBIS] IV curve question...
The simulator should do that automagically.
Ben
> -----Original Message-----
> From: ruston, matt [mailto:ruston_matt@emc.com]
> Sent: Friday, November 01, 2002 11:33 AM
> To: 'Ingraham, Andrew'; ruston, matt
> Cc: ibis@eda.org
> Subject: RE: [IBIS] IV curve question...
>
>
> Andy:
>
> Hi. The non-monotonicity is attributable to the separation
> of the various
> clamp and pulldown curves. I added the clamp curves back in
> (in Excel) and
> the curves looked normal.
>
> Does anyone know of an easier way to combine these clamp
> currents back with
> the pullup and pulldown curves? Any freeware utilities?
>
> Regards,
>
> Matt
>
> -----Original Message-----
> From: Ingraham, Andrew [mailto:Andrew.Ingraham@hp.com]
> Sent: Thursday, October 31, 2002 2:14 PM
> To: ruston, matt
> Cc: ibis@eda.org
> Subject: RE: [IBIS] IV curve question...
>
>
> Matt,
>
> I didn't know that the supply voltage was only 1.8V. Since in
> your sketch the non-monotonic region begins around there, it
> is possible that the non-monotonicity is related to the
> separation of currents into pull-down and clamp I-V tables.
>
> The spikeyness almost sounds like a simulator bug, especially
> with the way you can affect the spike by changing Tstep.
>
> Regards,
> Andy
>
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