Re: Spice Model of IBIS

Hi Fred,

  Ouch, here are my responses to your points:

> 3) SPICE has no rules so there is no minimum requirements to be a spice model.
> IBIS models provides sufficient detail about the component characteristics to
> allow signal integrity, EMC analysis and high speed design work. Since
> SPICE models don't have any agreed upon standards there is no way to tell if the
> information needed will be present and where to find it.
>Fred Said: "IBIS as it stands has not been approved for EMC and it's untested"
Several companies are using IBIS models as stimulus for EMC
related products and have tested them.
Yes there are more physical package related issues that need to be added to
improve the accuracy.
SI analysis had many years head start on EMC analysis and I feel considerable
improvement can be made in this area in the future.

> 4) There is no way to embed testing specifications in SPICE. IBIS contains
> testing constraints as well as device characteristics.
>Fred Said: "I don't have a clue what Kellee is talking about. Is the embeded test
> the load resistance to test the model under?"
These are things like threshold voltages, min and max specifications
Vmeasure specification for flight time adjustments which allow the simulator
delays to be used with timing tools.

> 5) SPICE has no way to indicate best/worst case limits the manufacturer
> wants you to design to, IBIS does.
>Fred said: This is bogus since IC desigers have been doing this for at least 30
> Now how is that possbible if Spice doesn't or can't indicate best/worst case limits?
We are talking about board designers not IC designers and board designers
need to use min/max limits specified by the IC vendor. And min and max design
limits are not provided by SPICE. Even something as simple as the power supply range
is missing from spice models unless perhaps it is there as a comment. Obviously spice
can be used to simulate and IC at best and worst case temperature and best and worse
case voltage etc. But the user must choose the limits unless they are obtained automatically
from a specification like IBIS. I don't see any reason why a SPICE package couldn't be
modified to do this though.

> 6) IBIS has been extended to include resistor and capacitor packages as
> well as diode packages. This can be done in SPICE, but there are again no rules
> about what information is present and how it is organized. This works OK
> (though a bit of extra work in a schematic level simulator) however it does not work
> very well if the model must be used at the board level and automatically
> loaded.
>Fred said: Not only can Spice to this but it can do this elequently, both at the
> schematic level and board level. Kellee you should learn more about
> using Spice subckts. It works wonderfully well at the board level thankyou,
> we've been doing this since 1992.
As I said schematic level can be done in SPICE.
If you have made some SPICE sub-circuits for some resistor packs at the board level
I would say great but I don't see any standard method for describing R,C,diode
packs emerging other than IBIS.

> 7) IBIS is also being extended to do connector models.
The IBIS specification is not complete in this area.
While SPICE can be used to model connectors there is no standards and
that includes lack of specification of standard methods for coupling matrix's.

Hopefully we will make some progress with IBIS in creating a connector
specification this year. I hope you will participate in this
effort as I know you and your company have a large amount of knowledge in this area.

-------------------------------------------------------------------------
Have a great day...
Kellee Crisafulli at HyperLynx
kellee@hyperlynx.com http://www.hyperlynx.com
-------------------------------------------------------------------------
Received on Mon Mar 30 19:21:38 1998