Robert and Bevan,

While I have not done any playing around with Protels Signal Integrity
capability, primarily because I haven't had the time and I know it will take
some study time to understand it's implementation and proper usage, and
secondarily because I know that models are somehow involved which means you
have to have a model for everything involved, which usually means that you
have to build some, and to do that properly, and make sure the ones you have
are good, you have to fully understand the models.

Anyway, even though I do not know anything about Protels implementation, I
have been following your posts on this thread here in the forum, and one
thing that was stated here kind of reached out and hit me over the head with
a club sized question mark.

If I understand what you have said regarding "loops" under "pads", it
appears that you are actually saying that Protel (in either the 99 SE or DXP
incarnation) cannot distinguish that the continuity of the trace "merged
with" (as it were) the continuity of the pad, or possibly a better way to
put it might be that the signal trace "transitioned" into a different, shall
we say conductor.

This is a little scary to me, in that it appears that it would therefore be
making improper calculations, especially if the calculations consider that
portion of the trace that extends under the pad as an extension or
continuation of the same trace for that specific length (whether it be in
addition to or in place of the characteristics of the pad itself).

It would appear that it may be ignoring the change in conductor
characteristics, and that from the perspective of capacitance (being
certainly more with respect to adjacent planes) and inductance (being
probably less), which both will effect impedance at least to the point of
being a discontinuity, and more importantly from the perspective cross talk
due to the change in environment to adjacent conductors, etc., etc..

All of this prompts me to wonder and question whether or not Protel takes
things that may drastically affect the characteristics of the signal
conductor into account, such as changes in conductor width, vias, and
transitions to different layers (with different relationships to planes
(read distances)).

Quite possibly I am worrying about things that appear to be trivial to most,
and quite possibly I am thinking of Protels SI capability far beyond its
intended design, but I am thinking of its usability and accuracy in terms of
a recent design which used two 16 bit LVDS controlled impedance differential
data busses operating at 500 MHz between 3 large BGA's, with BGA termination
packs in the middle of the whole thing.

One of the very unfortunate side effects if using high density BGA's is the
fact that you are sometimes forced to use vias to get into or out of the
connection array, which forces you to use these vias on a signal conductor
that you otherwise would never dream of using a via on.

At these speeds, and especially in a controlled impedance environment, these
kinds of things, and things like recognizing a loop under a pad that in
reality is not even there from the electrical perspective, make me wonder
just what the Protel (99SE/DXP) Signal Integrity capabilities really are,
and whether or not it is even realistically usable, and therefore worth the
time to learn how to use.

In my recent designs I have dealt with one RF Engineer who really is worried
about the size and shape of the pads on the components of a 1 GHz
synthesizer, down to the point of the direction that the trace has to enter
the pad, and with another RF Engineer who wants to use 20 mil controlled
impedance traces which go directly into the pads of an 0402 component
without any width transitions, which also have the ground plane cleared away
under the component to compensate for the capacitance introduced by the body
of the component itself (this is in a 2.75 GHz RF / Fiber Optic design).
These are the types of things that I am dealing with that prompt me to ask
the kinds of questions I am asking.

>From your guys experience and familiarity with Protels SI capability, am I
just worrying over minutiae, or stuff that doesn't really even enter into
the picture, or am I thinking way over Protels (99SE/DXP) capability.

Another question that I have about Protels SI capabilities, is whether or
not, when it models traces that are over a ground (or other) plane, does it
simulate a solid (imaginary) ground plane, or does it take into account the
actual topography of the actual ground under the trace, including any gaps
or splits due to clusters of vias or thru hole component pins, or things
such as thermal reliefs. Actually, for that matter, does it deal with the
real topography of the trace itself, or does it just simulate a trace of x
length and y width and let it go at that.



----- Original Message -----
To: "Protel EDA Forum" <[EMAIL PROTECTED]>
Sent: Thursday, October 10, 2002 9:52 AM
Subject: Re: [PEDA] signal integrity

> >> the copper. I fixed the loops and SI worked great.
> >
> > So I should probably get DXP back to find these kind of errors...
> >
> Well it does do a bit better job at it, and from the sounds of it the
> first Service pack will fix almost all the issues and requests for
> improvements.
> >> Once you take over a net you can double click on a pin in the net and
> >> change the model and stimulus for that pin.
> >
> > Is there a way to assign a component a whole IBIS file (ie the IBIS file
> for
> > that component includign pins etc) as opposed to just each individual
> pin??
> > I was thinking in terms of a component properties entry or similar.  ie
> In
> > the PCB or Schematic workflow...
> This is another area where DXP improved things. It is much easier to
> assign models to a component and they stay with it since you assign them
> while creating an integrated library.
> I have noticed with 99SE that once you assign a model to one pin the other
> pins of that type get most of the fields from that one. Unfortunately not
> all the fields carry over.
> Robert D. LaMoreaux

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