RE: [SI-LIST] : Accuracy of HSPICE W-element transmission lines

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From: Ted Mido (mido@avanticorp.com)
Date: Tue Nov 28 2000 - 10:13:44 PST


Right it should be 2000.4. Because I've just past old draft, the last paragraph
looks meaningless. Thank you for pointing it out.

        ted

From: "Chan, Michael" <Michael.Chan@compaq.com>
Subject: RE: [SI-LIST] : Accuracy of HSPICE W-element transmission lines
Date: Tue, 28 Nov 2000 08:17:41 -0600

> Ted:
> In your second last paragraph below, is it a typo error? Is it supposed
> to be 2000.4 instead of 99.4? Thanks.
>
> Michael Chan
>
>
> -----Original Message-----
> From: Ted Mido [mailto:mido@avanticorp.com]
> Sent: Monday, November 27, 2000 7:59 PM
> To: david.kaiser@mcdata.com
> Cc: ldmiller@nortelnetworks.com; keskinen@nortelnetworks.com;
> si-list@silab.eng.sun.com
> Subject: RE: [SI-LIST] : Accuracy of HSPICE W-element transmission lines
>
>
>
> Dear SIers,
>
> I am a developper of hspice and currently taking in charge of W-element.
> You may have seen following information on W element feature from
> the person who had been taking in charge of W element. But for those who
> haven't read seen it I would like to resend this by adding up to date
> information. Please take a look at this.
>
> ---
>
> I would like to clarify the four Hspice issues which have been
> actively discussed:
>
> 1) Accuracy of the field solver for computing the skin-effect
> matrix Rs.
> 2) Discussion of the inclusion of the imaginary term for Rs:
> SQRT(f)*Rs [eq1] vs. SQRT(f)*Rs*(1+j) [eq2].
> 3) Discrepancy between the transient and ac analysis results for
> the cases with non-zero Gd values.
> 4) Discrepancy between the transient analysis results using
> a single long line versus several short lines.
>
> (1) It is clearly stated in the Hspice manual that the computation
> of Rs does NOT account for any proximity or edge effects; hence,
> the resulting value is significantly smaller than the actual value.
> This is consistent with the computed data by Richard Mellitz.
> We are currently working on implementing a new solver which
> accurately models the skin, proximity and edge effects.
> For 2000.4 release, we have implemented a new field solver which
> is for skin effect resistance and inductance which have following
> features.
>
> Advantage:
>
> 1. Effects due to magnetic coupling such as skin effect
> and proximity effect can be modeled.
> 2. Resistive ground plane is taken into account (but not in C and G).
>
> Side Effect: (*important*)
>
> 1. Rs has off diagonal components due to magnetic coupling
> 2. Lo becomes bigger than previous extraction because of
> proximity effect especially under the condition of high
> resistive ground plane.
>
> Limitation:
>
> 1. due to the limitation of "RLGC" model input (only real value),
> imaginary part of Rs is ignored. this may cause error in
> high frequency R,L value. In fact Rs is computed to fit
> the formula [eq.2] which models skin effect resistance.
> (in future release, this will be solved by changing the
> output to "frequency tabular RLGC model" which is
> implemented in 2000.4 described below.)
>
>
> (2) The main issue for this second problem is that while including
> the imaginary term [eq2] models the skin effect (marginally) better
> at high frequencies, it may introduce a significant error at low
> frequencies. Some people, especially those working on high
> frequency applications, are accustomed to use [eq2] while others
> prefer [eq1].
>
> I prefer to use [eq2] since it is mathematically more valid solution
> at the high frequency range where the SQRT(f) dependency is valid,
> and furthermore, both equations are not accurate at low frequencies
> anyway. I ran some test cases using both equations and observed no
> significant differences in ac analysis. However, the accuracy of
> the transient analysis is slightly degraded when [eq1] is used.
>
> Nonetheless, we will change the implementation so that you can
> optionally exclude the imaginary term.
>
> (The ultimate solution to this Rs problem, as it has been pointed
> out by Michael Tsuk, could be to use a better modeling equation
> or even tabular data.)
>
> (3) The difference in attenuation between transient and ac analyses
> with non-zero Gd values is a rather subtle problem. The cause of
> this problem is mainly due to the limitation of the dielectric
> model equation based on f*Gd as has been pointed out by Dmitri.
>
> (4) The discrepancy between the transient results using a single
> line versus several cascaded short lines is mainly due to the
> limitations on the difference approximation routine used in
> W-element for the frequency-dependent cases. Recently, we have
> significantly improved the difference approximation routine, and
> and this discrepancy has been eliminated. (No risetime parameter
> setting is necessary anymore.)
>
>
> All of these improvements will be available for the next release
> of Hspice (version 99.4). We will soon make a beta version available
> (approximately 1 month); however, the new solver mentioned in (1)
> won't be implemented in this beta version.
>
> I hope this note clarifies all the issues related to the W-element
> and field solver in Hspice.
> I apologize for a somewhat late response.
>
> Regards,
>
>
>
> : Ted Mido
> : Avant! Corporation (Oregon R&D)
> : 9205 SW Gemini Drive
> : Beaverton, Oregon 97008
>
>
> From: David Kaiser <david.kaiser@mcdata.com>
> Subject: RE: [SI-LIST] : Accuracy of HSPICE W-element transmission lines
> Date: Mon, 27 Nov 2000 17:28:12 -0700
>
> > Nope. This is conjecture based on my expectations and experience. But
> > when I confronted a support person at Avanti, he addmitted that there
> > may be limitations above 1GHz.
> >
> > David
> >
> > -----Original Message-----
> > From: Larry Miller [mailto:ldmiller@nortelnetworks.com]
> > Sent: Monday, November 27, 2000 11:53 AM
> > To: David Kaiser; Kai Keskinen; si-list@silab.eng.sun.com
> > Subject: RE: [SI-LIST] : Accuracy of HSPICE W-element transmission lines
> >
> >
> >
> > Yes, but have you compared your results (either) with real hardware?
> >
> > Inquiring minds want to know....
> >
> > Thanks,
> >
> > Larry Miller
> >
> > -----Original Message-----
> > From: David Kaiser [SMTP:david.kaiser@mcdata.com]
> > Sent: Monday, November 27, 2000 10:17 AM
> > To: Keskinen, Kai [KAN:0G15:EXCH]; si-list@silab.eng.sun.com
> > Subject: RE: [SI-LIST] : Accuracy of HSPICE W-element
> > transmission lines
> >
> > I have compared the W-element with the RLGC matrix from running
> > APSIM on 100 Ohm diff'l pairs). With a 30ps pulse and 10ps rise times,
> > the reflected pulse was very symetrical for the W-element, but showed
> > and RC roll off with APSIM. The APSIM seemed to shown a more realistic
> > reflection pulse.
> >
> >
> > David Kaiser
> > McDATA Corp.
> > 310 Interlocken Pkwy.
> > Broomfield, CO 80021
> > (303) 460-4431
> > davidk@mcdata.com
> >
> >
> >
> > -----Original Message-----
> > From: Kai Keskinen [ mailto:keskinen@nortelnetworks.com
> > <mailto:keskinen@nortelnetworks.com> ]
> > Sent: Thursday, November 23, 2000 11:19 AM
> > To: si-list@silab.eng.sun.com
> > Subject: [SI-LIST] : Accuracy of HSPICE W-element transmission lines
> >
> >
> >
> > Hello SI-People:
> >
> > We have now several times encountered differences in results
> > from other modelling packages and results from HSPICE w-element models
> > for applications involving fairly long striplines > 30cm on FR4 and
> > GETEK with 2.5Gbps signals with ~100ps edge rates. The W-element model
> > appears to give lower loss than the other techniques. Typical track
> > widths are 6-8 mils with 100Ohm loosely coupled differential pairs.
> >
> > Avant! claims the W-element method is accurate without providing
> > a paper showing how it was validated.
> >
> > How does the rest of the SI community feel about the accuracy of
> > the W-element model?
> >
> > Thanks in advance,
> >
> > Kai Keskinen
> > Equipment and Network Interconnect
> > Nortel Subsystems and Performance Networks (NSPaN)
> > (613)-765-3506 (ESN 395)
> > keskinen@nortelnetworks.com
> >
> >
>
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