[SI-LIST] Re: HSPICE W element field solver model
- From: "Michael Allen" <mallen@xxxxxxxxxxxxxxx>
- To: <si-list@xxxxxxxxxxxxx>
- Date: Sat, 9 Jun 2001 21:49:09 -0400
Alex,
Your analysis os valid, but the termination of 100 ohms across
the diff pair is standard and depends on the receiver that it is
driving. An internally terminated receiver amp may have a 50 ohm to
ground or in another case such as a CML receiver the inputs are
terminated to VDD
> -----Original Message-----
> From: Alex Horvath [SMTP:alexh@xxxxxxxxxxxxxxxx]
> Sent: Friday, June 08, 2001 1:53 PM
> To: si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Re: HSPICE W element field solver model
>
> Of course, you have to take in account the driver-receiver. The
> differential
> receiver we are using at 2.5 G will work down to a 200 mv differential
> voltage. The driver outputs a 1600 mv signal to 50 ohms. Still, it
> seems
> that the prudent designer would at least attempt to calculate losses.
>
> On a side note, the termination scheme they use is a little strange to
> me.
> The receiver has a 100 Ohm resistor between the +/- receive terminals
> but
> there is no 50 ohm termination to ground. The 50 ohm to ground
> terminations
> are located at the driver. I guess their reasoning is that common mode
> voltage (ie. reflections on the 50 ohm pair to ground) will be
> cancelled out
> so no need to terminate at the receiver. The transmission line is
> specified
> for 100 ohms differential impedance, 50 ohms to ground. Is my logic
> valid?
>
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx
> [mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Larry Miller
> Sent: Friday, June 08, 2001 10:38 AM
> To: 'si-list@xxxxxxxxxxxxx'
> Subject: [SI-LIST] Re: HSPICE W element field solver model
>
>
> The backplane companies like Tyco seem confident about it, and they
> have
> been building back- and mid-planes for telcos for years.
>
> It will be interesting to see where this goes.
>
> Larry Miller
>
> -----Original Message-----
> From: Alex Horvath [mailto:alexh@xxxxxxxxxxxxxxxx]
> Sent: Friday, June 08, 2001 10:31 AM
> To: si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Re: HSPICE W element field solver model
>
>
> Chris,
> I found your statements below very interesting because we have a
> consultant
> working for us that's telling us 3 gig on a FR-4 backplane (20") is no
> big
> deal. I told him I had some concerns based on the chip manufacturers
> data
> which recommended GETEK or similar. Do any simulators take losses into
> account?
>
> Are there any publications or papers that discuss in more detail the
> DK and
> loss tan you mentioned below? This is the first time I have worked at
> frequencies where this is a concern.
>
> Thanks, Alex H
>
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx
> [mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Chris Mesibov
> Sent: Friday, June 08, 2001 4:58 AM
> To: si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Re: HSPICE W element field solver model
>
>
> Most PCB fabricators and their lamenate suppliers don't characterize
> FR4
> above
> 1.5 GHz (i.e. for DK and loss tan). Therefore specifying controlled
> impedance
> lines intended for this bandwidth should be rejected by any fab house
> worth
> their salt.
> The problem is that the studies of FR4 at frequencies up to 10Ghz show
> dramatic
> changes in loss tan and DK over freq and temp. What this would result
> in
> for
> digital signals is group delay and rise time degradation. Group delay
> is
> when
> the fourier components of the waveform propagate down the transmission
> line
> at
> different rates. The rise time degrades because as the frequency
> increases,
> so
> does the loss tangent. This has the effect of attenuating the
> harmonics of
> the
> waveform, thus slowing the rise time.
>
> Hope this sheds some light.
>
> Chris
>
> Alex March wrote:
>
> > Dear SI experts,
> >
> > I would like to ask about your experiences with the
> > W element field solver model in HSPICE. I am trying to
> > make some simulations in the Gigahertz range with FR4
> > material and I am not sure about what value I should
> > use for the conductivity of FR4.
> >
> > Thank you,
> >
> > Alex
> >
> >
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>
> --
> Chris Mesibov
> Sr. Hardware Engineer Fujitsu Network Communications, Inc.
> Phone:(845)731-2037 2 Blue Hill Plaza, 6th Floor
> Fax: (845)731-2011 Pearl River, NY 10965
>
>
>
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