RE: [SI-LIST] : Looking Inside IBIS Model

Beal, Weston (Weston.Beal@COMPAQ.com)
Wed, 19 May 1999 09:23:50 -0500

Steve,

Now I see your point. This is definitely correct mathematically, but I
still feel uneasy about it. I think that in reality, this should not
happen. If your TIME_TO_VM falling is much longer than rising, then your
simulation time to the receiver should also be much longer. The pulldown is
just not as strong.

So, your example is correct, but if you actually got these numbers from a
simulation, then I would look closely at all the parameters and test loads.
I won't say that it's wrong, but I would double check it.

Regards,
Weston

-----Original Message-----
From: TING.STEVE@inventec.com.tw [mailto:TING.STEVE@inventec.com.tw]
Sent: Wednesday, 19 May, 1999 2:51 AM
To: 'si-list@silab.eng.sun.com'
Subject: RE: [SI-LIST] : Looking Inside IBIS Model

Weston,
Thank you for your comment.
In my example, I try to express the idea:
The Tco_max was 2.5nS in my example, which was based on the same test
loading used to generate TIME_TO_VM.
And after Quad's mtest's calculation, I'll have TWO different values for
TIME_TO_VM: 0.8nS for rising and 1.8nS for falling.

I'll then think that the Tco_max must came from falling and the real Tco for
rising should be smaller than 2.5nS, maybe

around 1.5nS (I guess, because 1nS difference on TIME_TO_VM).
Then If I can have longer allowable flight time about 4nS (7.5-1.5-2.0=4.0)
purely for rising.
If it is true, the Tflight_rise of 3.1nS(<4.0nS) won't break my timing! Am I
totally wrong?

By the way, I assume zero skew and jitter in my formula just for
simplication, I didn't mean I can really do that in practical.

And I won't do the TIME_TO_VM correction manually in my simulation, I'll
enable the VM correction function in Quad if I have

reliable TIME_TO_VM values in XTK models.

RGS,

Steve Ting

-----Original Message-----
From: Beal, Weston [ mailto:Weston.Beal@COMPAQ.com
<mailto:Weston.Beal@COMPAQ.com> ]
Sent: Wednesday, May 19, 1999 12:21 AM

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