[SI-LIST] Re: Algorithm to interpolate ramp data in IBIS

Raghavendra,

Unfortunately I can't give you ideas how to make better use of
s2ibis2, since I am not using it.  I can only tell you that your
observations seem to be correct based on what I hear from my
colleagues.  Two major problems I see with that tool is that
it has evenly distributed points on both the IV curves and the
waveforms, and that the IV curves are generated by a .DC sweep,
and not in the time domain.  It is true that it can be done as
a .DC sweep, but this may not work under all conditions, while
doing it in the time domain (using .TRAN) would work more
universally.  I hope that the developers at NCU will some day
change these shortcomings.

There are other tools out there which do not have these problems,
but I do not want to upset anyone by naming them.  Some are for
sale, others are for free.

Arpad Muranyi
Intel Corporation
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D

-----Original Message-----
From: rkulkarn@xxxxxxxx [mailto:rkulkarn@xxxxxxxx]
Sent: Monday, November 24, 2003 6:16 PM
To: Muranyi, Arpad
Cc: si-list@xxxxxxxxxxxxx
Subject: Re: [SI-LIST] Re: Algorithm to interpolate ramp data in IBIS



Hello  Arpad,

Please correct me if I'm wrong:
s2ibis2 evenly spaces the points for Rising/Falling waveforms. Also the =
end
points are decided by DC operating points generated through 50-ohm-Vcc =
and
50-ohm-gnd conditions. So that way these end points and intermediate =
time-steps
are fixed (total time/no of steps).

So the question is:
Is there a better way to generate these curves using s2ibis2? or should =
you
write a tool to iteratively interface with hspice to generate these =
curves?

Any feedback is appreciated!

Thanks!
-Raghavendra


Is there a way to inform
"Muranyi, Arpad" wrote:

> 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
> =
=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D=
3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D
> =
=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D=
3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D
> =3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D
> -----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 =
=3D
> issue
> with the rampup/down portion.  If I have a hundred (or fewer) points =
in =3D
> a
> rise or fall section with each point being sampled at a regular =3D
> 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 =
=3D
> ramp
> up/down curves to reduce the number of points required for a given =3D
> accuracy.
> Unfortunately, I have been unable to definitevely find an algorithm =
used =3D
> 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 =3D
> of
> the desired timepoint.
>
> My understanding so far is that to extrapolate any values at times =3D
> either
> before or after the endpoints of the curve, the last two points are =
=3D
> 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? =3D
>  If
> so, then certain points can be removed if they can be obtained by two =
=3D
> 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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