Subject: RE: [IBIS-Users] Correlating Tco of IBIS to SPICE
From: Douglas Burns (dburns@sisoft.com)
Date: Wed May 21 2003 - 10:02:26 PDT
Tim,
IBIS contains no delay information, thus you can't compare them directly
with spice. Also, the spice file may not contain the full logic path delay
and it's output delay may not be the same as the spec'ed Tco. What you
really care about is that the waveforms overlay each other (when properly
shifted) when they drive the same load. For Timing analysis purposes, you
would then run a simulation of the IBIS into the standard load and a second
simulation of the IBIS into the actual load. You can then subtract the delay
from stimulus to response of the standard load simulation from the stimulus
to response of the actual load. The resulting data is the delay the actual
load has on the network with respect to the standard load. You then add the
Tco value (delay into standard load) to this computed value (delay of actual
network with respect to the standard load) to calculate the actual delay of
the full network.
Doug
Douglas Burns
Chief Consultant
Signal Integrity Software Inc.
6 Clock Tower Place
Maynard, MA 01754
978-461-0449 x14
www.sisoft.com
dburns@sisoft.com
-----Original Message-----
From: owner-ibis-users@eda.org [mailto:owner-ibis-users@eda.org]On
Behalf Of Timothy Coyle
Sent: Wednesday, May 21, 2003 11:25 AM
To: IBIS List
Subject: [IBIS-Users] Correlating Tco of IBIS to SPICE
Hello,
I am trying to correlate the rising Tco of IBIS file to original SPICE file.
To obtain the rising waveform for IBIS, I applied a PWL
source to the input, starting at time 0ns, and 300ps later reaching Vcc.
(300ps is the slew rate of the device) Since this is a clocked
output, I then apply a PWL to the clock input. So at about 1ns, I get my
rising waveform. When I run the SPICE file into the standard load (Vref,
Rref, Cref) and get the Tco number, it is 800ps, where the IBIS Tco is
1.53ns. I apply the same signal to both the SPICE and IBIS input, with no
delay and rise/fall times of 300ps. So depending on how I set up my clock
input, that is where my rising waveform will
start, and hence my IBIS Tco number. Is it acceptable to get rid of leading
zero's to match up IBIS to SPICE? Or should I be able to handle
this with the way I set up my inputs?
Regards,
Tim
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