**From:** Chris Rokusek (*crokusek@viewlogic.com*)

**Date:** Mon Dec 13 1999 - 10:32:47 PST

**Next message:**Grasso, Charles (Chaz): "[SI-LIST] : Power Bus Structures - Presentation now available!!"**Previous message:**Bradley S Henson: "Re: [SI-LIST] : IBIS models at Gbit speeds"**In reply to:**Laurence Michaels: "Re: [SI-LIST] : IBIS models at Gbit speeds"**Next in thread:**D. C. Sessions: "Re: [SI-LIST] : IBIS models at Gbit speeds"**Reply:**D. C. Sessions: "Re: [SI-LIST] : IBIS models at Gbit speeds"

Laurence,

An mildly-improved linearization technique was added to IBIS2XTK as of V5.01

(released March/99). The man page ($QUADHOME/man/cat1/ibis2xtk) hints at

how it works:

-deg_vi <val> Maximum Degrees Error for VI linearization. The

"degree" method of linearization is the default with

V4.92++. Use -old_vil to revert back to the -ae

method of linearization. Essentially the new method

is the same as prior but works out to be more uniform

over the entire range of the curve. A Lower deg_vi

is more accurate. A negative value (-1.0) may be

used to effectively disable linearization. The

tangent of this value is used to limit the ratio

of "error distance" to "point to point distance".

Note that the current tolerance also affects the

number of points in the resultant curve. The

allowed range is (-90.0 < val < 90.0) although only

-1.0 to 45.0 is practical.

-deg_vt <val> Max Degrees Error for VT linearization. The

"degree" method of linearization is the default with

V4.92++. Use -old_vtl to revert back to the -ae

method of linearization.

<snip>

Before continuing let me point out that changing the default values of these

arguments is likely NEVER TO BE NECESSARY...But of course some engineers

like to tweak so on with the explanation:

Without reverting to ASCII art, consider three sequential points A, B, C at

the elbow of a curve. The algorithm is stepping through all points on the

curve and eventually needs to test point "B" to determine whether it is

useful or redundant in relation to its neighbors. Drawing a triangle ACB

and then drawing a line that intersects the AC line (call this intersection

point X) at 90 degrees creates right triangles AXB and CXB.

Now point B can be removed if either of the following are true:

1) The important geometric measures in these triangles that are related to

the error of removing point B are the ratio of lengths XB to AX and on the

other side XB to CX. If the tangent of this ratio is less than or equal to

the -deg_* command line arg for this curve then the point can be removed.

2) If the "Y-axis" component (current or voltage) of the segement XB is

less than the tolerance (either voltage/current using -vt,-it) than it can

be removed. The primary purpose if -vt/-it is to remove measurement

"jitter."

The prior method that uses -ae does not preserve the elbow quite as nicely

and pays a bit too much attention to values near the y-axis.

I have purposely left out details of exactly how the algorithm steps through

all points in the curve.

The reason for reducing the number of points is to decrease simulation time

and decrease file size without any significant loss of accuracy.

Chris Rokusek

Viewlogic Systems

*> -----Original Message-----
*

*> From: owner-si-list@silab.eng.sun.com
*

*> [mailto:owner-si-list@silab.eng.sun.com]On Behalf Of Laurence Michaels
*

*> Sent: Monday, December 13, 1999 6:13 AM
*

*> To: si-list@silab.eng.sun.com
*

*> Subject: Re: [SI-LIST] : IBIS models at Gbit speeds
*

*>
*

*>
*

*> > John Lin (ªL´Â·×) wrote:
*

*> >
*

*> > Hi,
*

*> > Indeed, XTK model contains a few number of points compared to IBIS
*

*> > after doing IBIS2XTK. However, plotting both, you will find that they
*

*> > are quite match with each other.
*

*> >
*

*> > XTK will automatically increase points at the truning corner of
*

*> > waveform. The accuracy of simulation is not suffered.
*

*> >
*

*> > John Lin
*

*> > SI engineer at Quanta Computer Inc.
*

*> >
*

*> >
*

*> >
*

*> > -----Original Message-----
*

*> > From: Jim Freeman [mailto:freeman@broadcom.com]
*

*> > Sent: Saturday, December 11, 1999 2:02 AM
*

*> > To: si-list@silab.eng.sun.com
*

*> > Subject: Re: [SI-LIST] : IBIS models at Gbit speeds
*

*> >
*

*> > Hi,
*

*> > To my knowledge, Quad and Viewlogic Xtk don't directly use IBIS
*

*> > models. Instead, there is a compiler the linearizes the IBIS models
*

*> > and drastically
*

*> >
*

*> > reduces the number of points that are used in simulation.
*

*> >
*

*> > Jim Freeman
*

*>
*

*> I believe this reduction of points can be influenced by using
*

*> IBIS2XTK switches
*

*> -vt <val> voltage tolerance in Volts
*

*> -it <val> current tolerance in Amps
*

*> -ae <val> absolute error (0.0 < val < 1.0)
*

*>
*

*> Exactly how these switches affect the output, and what the default
*

*> values are, does not seem to be documented anywhere. Anyone from
*

*> Viewlogic/Quad care to comment?
*

*>
*

*> Regards,
*

*> --
*

*> Laurence Michaels
*

*> PS, if you have a vacation or "out-of-the-office" auto-response
*

*> program, please make sure it ignores mailing lists. For info,
*

*> contact your local system administrator.
*

*>
*

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**Next message:**Grasso, Charles (Chaz): "[SI-LIST] : Power Bus Structures - Presentation now available!!"**Previous message:**Bradley S Henson: "Re: [SI-LIST] : IBIS models at Gbit speeds"**In reply to:**Laurence Michaels: "Re: [SI-LIST] : IBIS models at Gbit speeds"**Next in thread:**D. C. Sessions: "Re: [SI-LIST] : IBIS models at Gbit speeds"**Reply:**D. C. Sessions: "Re: [SI-LIST] : IBIS models at Gbit speeds"

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