Re: [SI-LIST] : Hspice: Windows vs Unix

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From: Kim Helliwell (khelliwe@acuson.com)
Date: Tue Apr 10 2001 - 13:18:58 PDT


Actually, accuracy isn't really the issue, or at least not in the
sense your management probably means it, Anthony.

SpecctraQuest uses a spice-like simulator, TLSIM, to do the work.
This simulator is a derivative of SPICE (I don't know which flavor),
and therefore has all the usual accuracy plusses and minuses of
any SPICE, including HSPICE.

In addition, TLSIM has a coupled transmission line model, and the
diode and transistor models have been removed, and the whole simulator
has been optimized for the problem it's intended to solve.

The question of whether TLSIM's coupled transmission line is more
or less accurate than HSPICE's W-element is one of the issues, and
I cannot quantify it, except that I've never seen any reason to
distrust either one. From that I conclude that they are probably
equally good.

The real issue you face is the classical conundrum of SPICE: that accuracy
of results depends on accuracy of the models. So the issue is: what's
more accurate: the manufacturer's original BSIM models of their buffers,
or their IBIS models? The answer is obvious, since presumably the IBIS
models derive from the SPICE buffer models (almost no one creates IBIS
models from lab measurements, you see). But IBIS models can be very
close to the buffer models they derive from, and it's possible to lose
very little accuracy in using them. Whereas you might not be able to even
get the buffer model. And then you are forced to use HSPICE's IBIS buffer
model, at which point the accuracy of the two is on an even footing, and
it's *MUCH* harder to use HSPICE in this way than to use SpecctraQuest.

So I think the accuracy issue is illusory. If your management has enough
confidence in you, you have a chance to educate him/her/them as to the
realities of the situation.

Personally, I've used SpecctraQuest a lot in the last 2 years, and HSPICE only
occasionally. I use it for 2 things: as a field solver when the problem is
not easily expressible in terms that SQ understands, and perhaps to create
an IBIS model when the vendor provides an HSPICE buffer model but no IBIS model.
A third possibility is when IBIS doesn't accommodate a particular type of
buffer.

So I think Tony has a good question, and it's also not clear to me what
value-added HSPICE provides in your management's view. There is some, but
perhaps not where they are looking for it.

Kim

Anthony Davidson wrote:
>
> Perhaps that's where I have seen your name.
>
> I am a new user to Hspice, and SpecctraQuest for that matter. But the
> opinions of my team leaders is that the tools that are able to do analysis
> on complete boards and board-to-board interconnects are not as accurate as
> Hspice. And Hspice is more accurate, however, the analysis of complex (many
> connections) boards is very difficult.
>
> Note that the "less accurate" and "more accurate" statements are the
> opinions of others and not necessarily quantifiable.
>
> Anthony Davidson
>
> -----Original Message-----
> From: Dunbar, Tony [mailto:tony_dunbar@mentorg.com]
> Sent: Tuesday, April 10, 2001 11:18 AM
> To: 'Anthony Davidson'
> Subject: RE: [SI-LIST] : Hspice: Windows vs Unix
>
> Hi Anthony,
>
> No, neither Nortel, nor Univ of Western Ontario. Maybe you've seen my name
> on the list or something.
>
> The reasoning behind my question is that the platform on which you're
> running the other tools might give some pointers to the H-SPICE platform
> choice. Actually, since you're going with SPECCTRAQuest, I don't really see
> the need for H-SPICE for the so-called "fewer, critical nets". On these
> nets, what is it you're looking for SPICE to provide that SPECCTRAQuest
> can't? I'm not saying there is never room for co-existance, because there
> often is. It's just the "more accurate" thing that intrigues me.
>
> Regards,
> Tony
>

-- 
Kim Helliwell
Senior CAE Engineer
Acuson Corporation
Phone: 650 694 5030  FAX: 650 943 7260

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