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

Do we have a terminology issue here?

"Flight time", as I have always understood it, is the delay from the
driver's output to the receiver's input, as compared to the driver's delay
into the reference load.  Simplistically, flight time is the number you add
to the driving device's Tco value to figure out the delay from the clock to
when the receiver's input switches.

(Yes, I know it can be more complicated than that, but I'm being unusually
brief).

The propagation VELOCITY of a Tline is a property based primarily, as you
say, on the surrounding dielectric.  The propagation DELAY of a Tline
depends primarily on the dielectric constant of the surrounding material and
the length of the line.

Bottom line, I think when I say "flight time" and you say "interconnect
delay", we talking about approximately the same things.  "Flight time"
specifically includes the idea of adjustment with respect to a reference
load, which the "driver input->interconnect->receiver o/p" methodology
doesn't need to deal with.

As for the ability to model the whole path as you mention, well, I guess
that depends on what models the silicon  vendors are willing to give us,
doesn't it?  But yes, I'm familiar with the technique and understand the
need to do just that as edge rates increase.

Thanks,

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 Venkataraman, Srinivas
Sent: Tuesday, August 07, 2001 2:07 PM
To: Coleman, Dave; 'we_r_frendz@xxxxxxxxx'; si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Question about Simulation in Spectraquest
Importance: High



The flight time will always remain the same and has nothing to do with a
well or poorly behaved
t-line. Whether the flight time is fast or slow depends
only on the dielectric constant of the substrate. This confusion is caused
because you are trying
to bucket the driver delay, receiver delay and the interconnect delay in
different bins. The best
way would be to model the whole path, driver input->interconnect->receiver
o/p and then quantify the
impact of fast and slow skew corners of the devices.

Srinivas

-----Original Message-----
From: Coleman, Dave [mailto:dave.coleman@xxxxxxxxx]
Sent: Tuesday, August 07, 2001 7:44 AM
To: 'we_r_frendz@xxxxxxxxx'; si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Question about Simulation in Spectraquest



Rahul,

For a well-behaved transmission line circuit, you are correct - the fast
corner conditions will yield the min flight time.  If you have a
not-so-well-behaved circuit (i.e., have signal ringback across threshold),
the fast corner conditions may cause the signal to settle later than for the
slow corner conditions, so you CAN get a larger flight time with the fast
corner conditions.

Dave

-----Original Message-----
From: whiz kid [mailto:we_r_frendz@xxxxxxxxx]
Sent: Monday, August 06, 2001 8:14 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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