[SI-LIST] Re: Algorithm to interpolate ramp data in IBIS
- From: "Muranyi, Arpad" <arpad.muranyi@xxxxxxxxx>
- To: <si-list@xxxxxxxxxxxxx>
- Date: Mon, 24 Nov 2003 11:50:32 -0800
Nitin,
You are absolutely correct, 100 evenly spaced points for
the waveform tables (and also the IV tables) are not
accurate enough in most cases.
However, the IBIS specification does not describe how the
point reduction should be done, nor does it specify how the
tools should interpolate when reading such tables. On the
other hand, the specification does say that the beginning
and end of the waveform tables assume that the buffer is
in steady state (i.e. they start and end with a 0 slope).
It also says that the x-axis points do not have to be
evenly spaced.
As far as I know, most tools use only linear interpolation,
but you need to ask your tool vendor how they do it on your
own about these details.
The tool I am using to make IBIS models does the following:
1) Extract the two end points, connect them with a virtual
straight line and check where this "new curve" has the
largest vertical distance from the original curve.
2) Pick up a new point at this largest distance, and connect
the three points of this "new curve" with two straight
lines, and check for the largest vertical distance again.
3) Loop this way until 100 points are picked up.
I hope this helps.
Arpad Muranyi
Intel Corporation
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-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of BHAGWATH,NITIN
(HP-Roseville,ex1)
Sent: Thursday, November 20, 2003 3:55 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Algorithm to interpolate ramp data in IBIS
Hello all,
I am trying to convert a spice buffer model to ibis, and am having an =
issue
with the rampup/down portion. If I have a hundred (or fewer) points in =
a
rise or fall section with each point being sampled at a regular =
interval,
then the resolution of the curve seems to be inadequate for my purposes.
I have been reading articles about selectively removing points in the =
ramp
up/down curves to reduce the number of points required for a given =
accuracy.
Unfortunately, I have been unable to definitevely find an algorithm used =
by
IBIS simulators to interpolate data points at timepoints not in the IBIS
file given two data points in the IBIS file at timepoints on both sides =
of
the desired timepoint.
My understanding so far is that to extrapolate any values at times =
either
before or after the endpoints of the curve, the last two points are =
linearly
extended. More critically (for getting a good algorithm for points
removal), is it valid to assume that a voltage can be obtained for any
arbitrary time by taking the voltages at the two closest timepoints, and
linearly interpolating at the desired time using these two given points? =
If
so, then certain points can be removed if they can be obtained by two =
more
extreme points. Would there be any issues if the resulting ramp up/down
curves no longer have points at regular intervals of time?
Any help is much appreciated.
Thanks
-Nitin Bhagwath
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