In addition to the standard load used to specify Tco (clock-to-out time) and the
two 50 Ohm loads mentioned by DC Sessions, I would like to recommend two other
loads. These loads can be used to correlate models with hardware and behavioral
(IBIS) with structural (SPICE) simulations.
The first load is an open transmission line probed at the far end. This load
allows you to verify the complex reflection coefficient of the driver, which is
a combination of the output impedance and the various capacitances associated
with the output. You need to make the transmission line long enough relative to
the edge rate so that the wave has a chance to bounce around 2 or 3 times.
The second load is a transmission line and a receiver or tri-stated driver.
This load double-checks the previous load and adds the turn-on characteristics
(both ac and dc) of any clamps that may be present.
It's also very important to verify input and output IV curves and pin
capacitances. I have found that a TDR is a pretty handy capacitance meter.
Some of my colleagues and I wrote up a document that provides a wealth of
details on how to do model correlation. It's called "The IBIS Accuracy
Specification," and you can find it under "accuracy" on the IBIS web site:
www.eigroup.org/ibis/ibis.htm. There's even a test board design there that
demonstrates how to make some of these measurements in the lab.
Good luck in your work. Many of us users are encouraged to find vendors like
you who are doing their best to insure model integrity.
Greg Edlund
Advisory Engineer, Critical Net Analysis
IBM
3650 Hwy. 52 N, Dept. HDC
Rochester, MN 55901
[email protected]
---------------------- Forwarded by Gregory R Edlund/Rochester/IBM on 07/21/99
10:59 AM ---------------------------
Mark Nass <[email protected]> on 07/20/99 07:33:05 AM
Please respond to [email protected]
To: [email protected]
cc:
Subject: [SI-LIST] : Best type of models, edge rates & load
There has been some discussion recently about parameters of parts
specified into 40pf caps and accuracy of models. I generate this type
of data for our devices for our own use and our customers. So I am
curious as to what people think would be the optimal way to generate
Tco, Tsu, jitter parameters and IBIS models so that they would be confident
they were getting exactly what they needed for signal integrity and timing
analysis. Any feedback?
Mark Nass
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