RE: IBIS to SPICE

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?

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.

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

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?
 

-- 
John Fitzpatrick   <John.Fitzpatrick@ln.cit.alcatel.fr>    
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