[SI-LIST] Re: Question about Simulation in Spectraquest

  • From: "Todd Westerhoff" <twester@xxxxxxxxxxx>
  • To: <we_r_frendz@xxxxxxxxx>, <si-list@xxxxxxxxxxxxx>
  • Date: Tue, 7 Aug 2001 10:05:43 -0400

Rahul,

Actually, your question is generic:

Should I pay attention to max_flight time with a fast driver?
Should I pay attention to min_flight time with a slow driver?

The answer is irrespective of the SI tool being used.

The answer to these questions is a qualified yes.  If your circuit is poorly
terminated, or impedances are poorly matched, a fast driver can cause enough
ringing that the "fast" case will have the longest settle time.  This is
especially true with large, poorly designed packages, as any of the SI
veterans can tell you.

Slow driver / min_flight is usually not a problem, and in certain cases
should be disregarded.  The reasoning is somewhat complex, and depends on
how you're doing your timing budgets.  In my experience, I've run into cases
(with large capacitive reference loads) where the slow driver / min_flight
was the shortest flight time of all, causing an apparent timing violation
that we disregarded on closer inspection.

Hope that helps,

Todd.

Todd Westerhoff
SI Engineer
Hammerhead Networks
5 Federal Street
Billerica, MA  01821
twester@xxxxxxxxxxx
ph: 978-671-5084

-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of whiz kid
Sent: Monday, August 06, 2001 11:14 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Question about Simulation in Spectraquest



Hi Gurus,
I have a question about the usability of the values
that spectraquest spits when doing a flight time
simulation. When I am doing a simulation with a fast
driver, fast transmission line, and fast reciever I am
more concerned with the Min switch time (Min flight
time). Is the settle time (max flight time) that SQ
displays a use ful parameter here??. Because to find
the max flight time u make use of the slow driver,
slow line, slow reciever. Am I missing some thing in
how to interpret the values.

Regards,
Rahul.

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