[SI-LIST] : Re: attenuation calculations

Craig Callen (ccallen@ironbridgenetworks.com)
Fri, 24 Apr 1998 10:26:06 +0100

Hello Juliusz,

Sorry for some left out info. It is a dual stripline configuration with
the total ground seperation at 16.7mils, ground planes are 1/2oz Cu.
My calculations of 0.25dB/in. were at 1GHz and I also just started using
the quad
2D-field solver and these are the results I am receiving from the field
solver for
conductor 1.

Rs=0.372(ohm-nsec^.5)/in. (skin effect resistance)
Rdc=0.15881ohms/in.
C=3.674pF/in.
L=9.085nH/in.
Gdc=0 (I did not know the conductance of the dielectric for FR4 (sigma))
Gdl=0.066mS-ns/in. (dielectric loss conductance)

What are you inputting as the conductance for the dielectric?
What formula did you use to calculate 0.3827dB/in.?
Is there an easy way to figure out differential impedance from the
field solver?

Thanks for the info.

Craig Callen

Juliusz Poltz wrote:

> Thursday, April 23, 1998
>
> Hello Craig,
>
> There are few open questions about your geometry. However, assuming
> that the frequency is 3 GHz, and your geometry is 1/2 oz Cu (0.7 mils)
> where FR-4 has 4.7 dielectric constant and a loss tangent of 0.018,
> our solver calculates the dielectric thickness (for a microstrip)
> equal to 3.415 mils. For this geometry, we calculate per inch:
>
> R=2.1234 Ohms
> L=7.8405 nH
> C=3.136 pF
> G=911.52 uS
>
> which could be translated into 0.3827 dB/in attenuation for 3 GHz. As
> you can see the resistance is twice your predicted value. However,
> our solver calculates the current distribution in the ground plane
> (which I assumed to be also 1/2 oz Cu) and provides the resistance of
> the entire current loop (signal + return).
>
> Sincerely yours
>
> Juliusz
>
> > ------- Forwarded Message Follows -------
> > Date: Thu, 23 Apr 1998 18:11:52 +0100
> > From: Craig Callen <ccallen@ironbridgenetworks.com>
> > To: "si-list@silab.Eng.Sun.COM"
> > <si-list@silab.Eng.Sun.COM> Subject: [SI-LIST] : attenuation
> > calculations
> >
> > Hello,
> >
> > I am currently investigating attenuation of pcb traces, at speeds
> > of ~1-3GHz, with the use of GETEK and FR4. The traces are 1/2oz
> > copper, 6mil width, 50 Ohm impedance. Unfortunately the only
> > calculations I can find are low-loss approximations. With these
> > formulas I am finding the attenuation due to dielectric loss being
> > 0.1db/in and attenuation due to metal being 0.15db/in, for FR4.
> > These attenuations were calculated with the FR4 tangent loss of .018
> > and AC Resistance approximated at 1 Ohm per in. I was wondering if
> > anyone out there has accurate formulas for attenuation and do my
> > calculations seem reasonable.
> >
> > Thanks
> >
> > Craig Callen
> > ccallen@ibnets.com
> >
>
> "Juliusz Poltz" <jpoltz@optem.com>
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