Re: IBIS Models or full spice netlist...?

Gus Panella (apanella@mcs.com)
Mon, 30 Dec 1996 21:13:37 -0600

SI List,

About this IBIS thing....

There is one other drawback (as compared to SPICE) of TODAY's IBIS
modeling options... mutiple coupled transmission lines....

As of the present IBIS specification, there is not a method of defining
multiple coupled line connector or PC board L,C, k matrices... Some IBIS
solver vendors do provide vendor specific solutions... but as of yet there
is not a "standard" method for multiple couple transmission lines such as
those found on PC boards and connectors....

Yes, it is possible to describe 1st order LC effects in the current IBIS
specification... which may (or may not) be good enough for semiconductor
package models or PC boards... I let you be the judge for your
application. But, if you need LC (and k) for greater than a single
adjacent line (i.e. a connector) you might want to better understand what
the present version of IBIS leaves out....

Now, this leads to another bit of not so good news, multiple coupled
transmission line models (if they consist of an LCk matrix from a feild
extractor) are generally quite larger..... These "passive" components will
greatly extend the solve times..... I have not been able to do comparisons
between SPICE or IBIS yet.... I do beleive that once the coupled line
spec. is finalized, this comparison might prove very interesting.... I do
believe it is possible that the solve times will be VERY vendor
dependent.....

Also, I'd like to take a moment to say that I am not involved with the
creation of IBIS solvers.. .. so I'm really out of my inference space.....
but I beleive (please correct me here if I am wrong) that the algorithhms
used to process the IBIS "passive" component model information are vendor
dependent (when not using a SPICE based solver)..... if this is true...
users of IBIS mods will need to understand EACH IBIS solver... and maybe,
IBIS model accuracy for "passive" components might be solver dependent.....
:(

Good news is that there will be a face to face meeting of the IBIS
committee around January 20th... and there are teleconferences for the
IBIS committee that are generally held once a week to ince every other week
(so the IBIS committee is actively trying to resolve the coupling issue)

My opinion is presently equiv. to that of Fred Balistreri:

>... lastly because of the above and more I would tend not to trust IBIS
>models at 100Mhz or above. There are some redeeming factors to IBIS. >If
one can get the IBIS models it is a good starting point to at least check
>the designs in a rather fast manner. The data can be incorporated into a
>higher level simulator as mentioned previously. Again accuracy is the
>key. Crosstalk at the hundreds of millivolt levels is ok with IBIS.
Critical >timing and ground bounce issues need to be resolved by using a
more >robust model such as Spice transistor level.

if someone needs better than 100 mv level crosstalk resolution a SPICE
solution and model might have an edge... ..

Best Regards,

Gus Panella
apanella@mcs.com