Re: [SI-LIST] : Some Semiconductors are Unnecessarily Fast

D. C. Sessions (dc.sessions@vlsi.com)
Wed, 14 Jul 1999 12:07:18 -0700

Francis Chiu wrote:
>
> Hi, Genttlemen,
>
> Try using the National BLVDS, the current 090 part is specified at 100Mhz
> bandwidth for multipoint bus, tests shows the current part with appropriate
> terminations
> is good up to 300Mhz. For signal integrity issues, the part has internal
> filters to take care the problems.
>
>
>
> Francis Chiu
>
> Roy_Leventhal@mw.3com.com on 07/14/99 06:08:00 AM
> To: si-list@silab.eng.sun.com@Internet
> cc: (bcc: Francis Chiu/Americas/NSC)
>
> Subject: Re: [SI-LIST] : Some Semiconductors are Unnecessarily Fast
>
> D.C.
>
> You have some really great ideas on the edge rate problem that I am immediately
> going to try.
>
> First, I'm working on a complex bi-directional backplane bus where we would like
> to increase the daughter card stub lengths a little. Simulation shows that the
> IBIS "Max" selection (Cadence = "Fast") on the supplier's model is just a hair
> too fast in that we start failing Noise Margin on a few slot/driver
> combinations.
>
> I will clone the model provided, slow down the V-T curve and/or edit the V-I
> curves for a slightly lower Vol. Re-simulation will then tell me if my Noise
> Margin problem is fixed. I can then go to my supplier(s) with a max edge rate
> specification that they can respond to in a businesslike manner.
>
> This kind of interactive proposal - counterproposal testing of design
> feasibility is just what early simulation and reality checking should be doing
> for both supplier and user. And, obviously, not just for edge rates.

Note:
<plug=unselfish>
If you're using a Windows machine (leaves me out) you can use
Hyperlynx' IBIS model editor. Depending on what you get, you
can do some degree of SI simulation interactively with editing
the models, which sounds like exactly what you want to do.

So far as I know, the Hyperlynx tool is the only one remotely
like that available. Bless 'em, they're really providing the
thing to model makers (blush!) as a service to the industry,
and if it helps them indirectly then more power to them.
</plug>

> Roy Leventhal wrote:
> >
> > D.C.,
> >
> > Some additional thoughts & questions:
> >
> > I use Cadence's SpecctraQuest/SigExplore to simulate the boards. Those tools use
> > IBIS I/O cell models. SPICE models would cause me lots of extra time and effort
> > to get into IBIS format. We have found topology simulation, timing guided
> > placement, impedance guided routing, etc. to be all very helpful.
> >
> > I STRONGLY advocate sanity checks very early in the process. For such checks can
> > we get "+/-20%" models early on?
>
> No prob. The standard-cell libraries have been IBIS-characterized since 0.6 micron.
> We've had some rough spots with model quality but we've taken them as opportunities
> to improve the modelling process. Customer feedback on matters like that is
> extremely critical (and on that I think I can safely speak for the other Si
> members
> of the IBIS committee.)
>
> Other companies may be different. After all, why should they go to the
> trouble? Unless, of course, your components acquisition team gets brutal
> with "no IBIS models? Don't bother bidding."
>
> Better yet, though, why don't you (plural: meaning customers) take charge of the
> process and start specifying device I/O with IBIS models in the first place?
> YOU know your application better than we do (or blinking well *should*!)
> That way our sales force, who are of course clueless, *have* to come to the
> Geek Force to make sense of things. As it is, they (mistakenly) think that
> they know what they're talking about with nonsense such as "4x driver" and
> "8 mA driver."
>
> Demand the moon, stars, and Aurora Borealis. You won't get them, of course,
> but at least we'll be talking -- and the engineers will actually be dialed
> in for a change. Sure beats hearing about it later.
>
> Oh, and BTW: make the IBIS model part of the purchase contract. If you get
> a batch of parts that are outside of the envelope, make the vendor eat 'em.
> It's long past time that my colleagues got religion in the only sure way.
>
> > There are several caveats. Of course we don't want to get into "you said - - -
> "
> > finger pointing of early, first cut models. Then too, I would guess that IBIS
> > models give you no process control information feedback. Lastly, more complex
> > topologies need more accurate, worst case models not usually avilable early
> on.
> > Unless you're designing into a standard process.
> >
> > What's your ideas on dealing with these issues?
>
> Love it. Keep in mind that we *are* using a standard process, so I can get you
> some pretty good models very early in the game. Better yet, as above, YOU do
> the IBIS models. It's not like SPICE, after all; you don't need access to
> burn-before-reading process tables. Don't take OUR word for what the limits
> are; we'll push them out as far as we think we can get away with it so that
> the yield points are better and we can be sloppier about the design
> granularity.
>
> One of our people put it very well recently. He pointed out that semiconductor
> companies don't make 'product'. We make 'parts', and YOU make 'product'.
> Until YOUR _products_ ship to revenue customers WE haven't succeeded. Making
> you get by with some silly library modeled after thirty-year-old
> multiple-emitter
> parts that were doing well to get two flip-flops into a 14-pin package and
> hold the clock-to-Q times to a few hundred nanoseconds -- now THAT is really
> dumb. It's also exactly what's going to keep on happening until customers
> start demanding real, meets-our-needs technology instead of data sheet
> templates copied off of French cave walls.

-- 
D. C. Sessions
dc.sessions@vlsi.com

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