RE: [SI-LIST] : How to model effect of vias on nearby traces?

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From: Aubrey_Sparkman@Dell.com
Date: Fri Mar 23 2001 - 07:56:06 PST


Bhavesh,
In addition to IE3D from Zeland, there are also 3d tools from Ansoft.
Probably there are other tools as well. But if you can follow good layout
practices, you probably don't need to worry. BTW, I would caution against
putting a via in between your differential pair.

Good luck!
Aubrey Sparkman
Signal Integrity
Aubrey_Sparkman@Dell.com
(512) 723-3592

> -----Original Message-----
> From: Jian X. Zheng [mailto:jian@zeland.com]
> Sent: Thursday, March 22, 2001 8:05 PM
> To: Patel, Bhavesh; Aubrey_Sparkman@exchange.dell.com;
> ldmiller@rhapsodynetworks.com; mgreim@sonusnet.com;
> si-list@silab.eng.sun.com
> Subject: RE: [SI-LIST] : How to model effect of vias on nearby traces?
>
>
> Hi, Mr. Patel:
>
> Please try our IE3D full wave electromagnetic simulator. It
> is perfect for
> the structure you want to analyze. Please do not consider full wave
> simulators are difficult to use. The IE3D takes seconds or
> minutes to solve
> your problem accurately. Our MDSPICE simulator can extract
> wide band SPICE
> model from the s-paramters generated from IE3D and it can
> even perform a
> time domain simulation on the s-parameters for your long interconnect
> structures.
>
> Best regards,
>
> --------------------------------------------------------------
> ---------
> Jian-X. Zheng, Ph.D
> Zeland Software, Inc., 48890 Milmont Drive, 105D, Fremont, CA
> 94538, U.S.A.
> Tel: 510-623-7162, Fax: 510-623-7135, Web: http://www.zeland.com
> ---------------------------------------------------------------------
> Special Announcements: (1) IE3D 8.0 is released. The IE3D 8.0 has
> implementation of boxed Green's functions, periodic Green's
> functions, and
> advanced iterative matrix solvers for large structures. Using the AIMS
> matrix solvers, you will be able to solve large RF IC and
> antenna array
> problems. An example of an 8 by 8 antenna array takes less
> than 100 MB RAM
> to solve on the AIMS III matrix solver. (2) The s-parameter
> SPICE simulator
> MDSPICE 2.1 is released. The MDSPICE 2.1 has a robust time
> domain engine
> accepting s-parameters from full wave simulators. Its time
> domain simulation
> normally can guarantee the causality conditions for lossy
> transmission lines
> longer than 1 foot. The MDSPICE 2.1 also features wide band
> SPICE model
> extraction, eye pattern display and non-linear modeling for
> both digital and
> analog circuits. (3) The FIDELITY 3.0 is formally released.
> It has many good
> features to enhance 3D modeling in wireless communications.
> --------------------------------------------------------------
> --------------
> --
>
> > -----Original Message-----
> > From: owner-si-list@silab.eng.sun.com
> > [mailto:owner-si-list@silab.eng.sun.com]On Behalf Of Patel, Bhavesh
> > Sent: Thursday, March 22, 2001 5:18 PM
> > To: 'Aubrey_Sparkman@Dell.com'; ldmiller@rhapsodynetworks.com;
> > mgreim@sonusnet.com; si-list@silab.eng.sun.com
> > Subject: RE: [SI-LIST] : How to model effect of vias on
> nearby traces?
> >
> >
> > Hi! I agree with Aubrey that no SPICE tool can look at the effect
> > of cahnge
> > in impedance when the trace is routed adjacent to an anti-pad or
> > via because
> > I tried playing with Specctraquest which gives you the
> parasitics of a
> > segment of a trace and the impedance remained the same when I
> > moved the via
> > away.
> > Do you know which field solver can look at this issue?
> Because I wanted to
> > see if I route a differential high speed trace around multiple
> > vias(forms a
> > hexagon when it encounters a via)if ther is any impedance change.
> > Thanks
> > Bhavesh
> >
> > -----Original Message-----
> > From: Aubrey_Sparkman@Dell.com [mailto:Aubrey_Sparkman@Dell.com]
> > Sent: Thursday, March 22, 2001 4:19 PM
> > To: ldmiller@rhapsodynetworks.com; mgreim@sonusnet.com;
> Patel, Bhavesh;
> > si-list@silab.eng.sun.com
> > Subject: RE: [SI-LIST] : How to model effect of vias on
> nearby traces?
> >
> >
> > Larry and Michael,
> > Can we agree that a trace through any pin field will see
> either no change,
> > higher impedance, or lower impedance, all depending on the design
> > of the pad
> > stack, trace width, and stackup?
> >
> > Bhavesh,
> > I would answer that no SPICE including HSpice can determine the
> > impedance of
> > a trace as it passes through a pin field. For that you
> need another tool.
> > To understand the effects of a trace going through a pin
> field, you need a
> > two step process. I think that all would agree that since these
> > effects are
> > geometry (trace width and pad stack design) and material
> > specific, you would
> > need either a TDR (after design) or a Field Solver to determine the
> > impedance of the trace as it passes through the pin field.
> >
> > Only after you determine those impedances can you use your
> > favorite SPICE to
> > determine the effect of those impedances on your signal. Of
> > course, if your
> > board is already designed and assembled, you can use a TDR
> > without SPICE to
> > look at those reflections.
> >
> > Aubrey Sparkman
> > Signal Integrity
> > Aubrey_Sparkman@Dell.com
> > (512) 723-3592
> >
> >
> > > -----Original Message-----
> > > From: Larry Miller [mailto:ldmiller@rhapsodynetworks.com]
> > > Sent: Thursday, March 22, 2001 4:50 PM
> > > To: 'Greim, Michael'; Larry Miller; 'Patel, Bhavesh';
> SI_LIST (E-mail)
> > > Subject: RE: [SI-LIST] : How to model effect of vias on
> nearby traces?
> > >
> > >
> > > Let's say for argument that a trace runs directly over
> the center of a
> > > circular antipad area on the reference plane, and the antipad
> > > diameter is
> > > larger than the trace width.
> > >
> > > Yes, there is no reference under the trace, but wouldn't the
> > > return paths of
> > > least inductance go around the rims of the circular antipad?
> > > That is not a
> > > much longer path length unless the antipad is huge, so maybe
> > > that is why
> > > there does not seem to be much effect.
> > >
> > > What seems to really affect things is where you have a gap
> > > such that the
> > > return currents have to seek a much longer path length.
> > >
> > > Hmmm?
> > >
> > > Larry Miller
> > >
> > > -----Original Message-----
> > > From: Greim, Michael [mailto:mgreim@sonusnet.com]
> > > Sent: Thursday, March 22, 2001 2:40 PM
> > > To: 'Larry Miller'; 'Patel, Bhavesh'; SI_LIST (E-mail)
> > > Subject: RE: [SI-LIST] : How to model effect of vias on
> nearby traces?
> > >
> > >
> > > Wouldn't part of the effect (perhaps a more significant
> > > part) be how big the antipad is on the reference plane and
> > > whether the signal in questions is routed over it or not?
> > > I have seen some antipad requirements so large that a trace
> > > could be routed over a wafer thin piece of plane to the
> > > point that the trace is essentially routed over no reference
> > > at all.
> > >
> > > Comments?
> > >
> > > Best Regards,
> > >
> > > Michael C. Greim Sonus Networks
> > > mgreim@sonusnet.com 978-589-8336
> > >
> > > Making the world safe for digital signals everywhere
> > >
> > > And all this science I don't understand
> > > It's just my job six days a week
> > >
> > > The time is gone. The email's over
> > > Thought I'd something more to say......
> > >
> > >
> > > -----Original Message-----
> > > From: Larry Miller [mailto:ldmiller@rhapsodynetworks.com]
> > > Sent: Thursday, March 22, 2001 4:42 PM
> > > To: 'Patel, Bhavesh'; SI_LIST (E-mail)
> > > Subject: RE: [SI-LIST] : How to model effect of vias on
> nearby traces?
> > >
> > >
> > > I have seen some high speed connector TDR plots where traces
> > > are routed
> > > through pin fields on back/midplanes. This is similar to
> > > passing near a via,
> > > even worse I would think. I have also done TDR's on our
> own boards.
> > >
> > > The effect seems to be very small (a few % of 50 ohms) and of
> > > short duration
> > > in time, which of course corresponds to very high frequencies
> > > (10's of GHz).
> > >
> > > One view.
> > >
> > > Larry Miller
> > >
> > > -----Original Message-----
> > > From: Patel, Bhavesh [mailto:bpatel@cyras.com]
> > > Sent: Wednesday, March 21, 2001 8:06 PM
> > > To: SI_LIST (E-mail)
> > > Subject: [SI-LIST] : How to model effect of vias on nearby traces?
> > >
> > >
> > > Hi! I wanted to know how do I simulate the effect on the
> impedance..
> > > reflection on a trace/signal when it is very close to a via.
> > > It does not go
> > > thru the via but passes very close to it. Can I model this in
> > > HSPICE? And if
> > > yes how/
> > > Thanks in advance
> > > Bhavesh
> > >
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