[SI-LIST] Re: Determining timing budgets using IBIS
- From: "Peters, Stephen" <stephen.peters@xxxxxxxxx>
- To: "'alexh1@xxxxxxxxxxxxx'" <alexh1@xxxxxxxxxxxxx>,si-list@xxxxxxxxxxxxx
- Date: Sun, 28 Jul 2002 15:14:45 -0700
Hello Alex:
Yes, if is possible to apply IBIS models to timing simulations in pretty
much the manner you describe. First, perform a simulation with the driver
model driving the same test load used to determine the devices propagation
or Tco delay. Note the time the output waveforms crosses the Vmeas voltage.
Next, perform a simulation with the IBIS model driving the real interconnect
and note when the waveform at the receiver crosses Vih(min) voltage. The
difference in time between when the output waveform crosses Vmeas (the first
simulation) and when it crosses Vih (the second simulation) is referred to
as the 'flight time' of the signal. Adding Tco and flight time (as apposed
to the simple propagation delay of the interconnect) is the methodology used
to arrive at timing calculations that take into account the effects of
output loading on a devices propogation delay. Also, as a note: most IBIS
compatible simulators will do this first simulation and calculate flight
time automatically for you.
Hope this helps.
Regards,
Stephen Peters
Intel Corp.
-----Original Message-----
From: Alex Horvath [mailto:alexh1@xxxxxxxxxxxxx]
Sent: Friday, July 26, 2002 8:29 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Determining timing budgets using IBIS
Using an IBIS model, I would like to determine the time it takes for the
voltage at the end of a transmission line to reach Vihmin from a clocked
output. As I understand it, IBIS output is not referenced from a clock
output and does not include chip delays.
If this is correct, is it possible to load the IBIS model with the load as
specified in the device data sheet (usually a 50pf lumped load or infinitely
long transmission line), and add a delay to the output of the model such
that the time to reach the specified output voltage matches the data sheet?
Then this delay can be used with the IBIS model and the transmission line of
interest to determine settling time.
If IBIS cannot be used to determine clock to settling time, then it seems
it's only useful for designing transmission lines and not timing analysis.
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