Re[2]: IBIS to SPICE

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Brian,

I would suggest that you drive that VCR with the voltage between the output node
and the ramp node. However, I would suggest not to use VCRs (as I stated to you
in my private EMAIL to you). A Thevenin or Norton circuit with voltage
controlled current or voltage source (and some tricks) will work better.

Arpad
================================================================================

John,

Thank you for replying. I have defined the voltage controlled resistors =
AOK in the manner you have described. Maybe it is a simple point I am =
stuck on. What voltage should I drive the voltage controlled resistor =
control line with? =20

My first thought was to drive it with a ramp having the rise time =
specified in the IBIS file. But then when I think about it a bit more I =
think that the voltage controlled resistor is also controlled by the =
voltage from VCC (or ground for the pulldown R) to the output voltage =
(Ccomp node). The table of (V, I) leads me to this question because of =
the range of voltages shown (2*Vcc, I think) which doesn't seem relevant =
for an internally generated ramp. =20

I'm certain this is just a matter of my own lack of understanding of the =
IBIS model. Thank you for taking the time to reply.

Regards,

BCW
Guided Wave Solutions

----------
From: John V Fitzpatrick[SMTP:John.Fitzpatrick@ln.cit.alcatel.fr]
Sent: Tuesday, January 14, 1997 9:46 AM
To: Brian C. Wadell
Subject: Re: IBIS to SPICE

Brian,
=20
This is a good approach. I don't understand your problem. The
V-controlled resistances can be defined directly by the IBIS tables.=20

For the pulldown case, your PWL will
be at 0V, so the V-controlled resistance will correspond
to the IBIS table directly. Similarly for pullup, your PWL
will be at Vcc, do you can use the Vcc-referenced IBIS table directly.

During the transition time of the PWL, you just hope for the best -
it's usually good enough. This is what I've seen from models I've
built (manually) in PSpice using IBIS data.

Regards,
John

> I'm not quite certain what the meaning of the pullup and pulldown =
should be with respect to the edge rate specified in the IBIS file. My =
thought was to create a PWL edge out of the edge rates and drive a =
voltage-controlled resistance having the pulldown characteristics with =
that voltage. However, the voltage in the IBIS pulldown table seems to =
be the voltage across the pulldown resistance/conductance?
=20
--=20
John Fitzpatrick <John.Fitzpatrick@ln.cit.alcatel.fr> =20
Alcatel Telecom, 4 rue de Broglie, 22304 Lannion, France
Tel: +33(0)2.96.04.79.33 Fax: +33(0)2.96.04.85.09

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Date: Tue, 14 Jan 1997 22:00:19 -0500
Subject: RE: IBIS to SPICE
Cc: "'ibis@vhdl.org'" <ibis@vhdl.org>
To: "'John V Fitzpatrick'" <John.Fitzpatrick@ln.cit.alcatel.fr>
From: "Brian C. Wadell" <bcwadell@guidedwave.com>
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