**From:** Fred Balistreri (*fred@apsimtech.com*)

**Date:** Fri Mar 17 2000 - 12:30:57 PST

**Next message:**Mayer, Mike: "RE: [SI-LIST] : Bad IBIS models!"**Previous message:**Adrian Shiner: "Re: [SI-LIST] : Bad IBIS models! - Business thoughts"**In reply to:**amit agrawal: "Re: [SI-LIST] : A basic question"

In the equation sqrt LC, the C is assumed to be total C, fringe included.

If the methods used do not compute fringe then the methods are at

fault not the equation.

Best Regards,

amit agrawal wrote:

*> In ideal situation, the progation delay is strictly dependent on Er. The
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*> proagation delay is given by
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*>
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*> tau = sqrt(Er)/30 ns/cm
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*>
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*> This is also equal to sqrt (LC)(Note: this condition is true only when C
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*> does not include the fringe field effect)
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*>
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*> When we use any EM tool to calculate the transmission line L and C per unit
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*> length, the capacitance may include the fringe field effect. In that case,
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*> the effective propagation delay is always more than the ideal propagation
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*> delay.
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*>
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*> tau(effective) = tau(ideal) + delta due to fringe-field
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*>
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*> The fringe field effect can vary with the geometry of the line.
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*>
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*> In reference to characteristic impedance, the ideal characteristic impedance
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*> is sqrt (L/C), where C is fringe-field-free. This can also be expressed in
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*> terms of ideal propagation delay as
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*>
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*> Zo (ideal) = tau (ideal)/C
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*>
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*> C depends on the geometry of the line for a given Er.
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*>
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*> Thus, if the Er is fixed, the capacitance and impedance can be changed by
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*> changing the geometry of the line.
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*>
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*> The capacitance, C calculated from EM tools is not fringe-field-free, hence
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*> the characteristic impedance is no longer ideal> we can refer it as
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*> Zo(effective). Note that Zo(effective) will always be smaller than the
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*> Zo(ideal).
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*>
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*> I hope this should answer your question.
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*>
*

*> Amit Agrawal
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*> Lightsand Communications
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*>
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*> >From: "Peterson, James F (FL51)" <james.f.peterson@honeywell.com>
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*> >Reply-To: si-list@silab.eng.sun.com
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*> >To: "'si-list@silab.eng.sun.com'" <si-list@silab.eng.sun.com>
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*> >Subject: [SI-LIST] : A basic question
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*> >Date: Fri, 17 Mar 2000 08:00:49 -0500
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*> >
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*> >SI List:
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*> >
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*> >I have a question about the relationship between Z and Pd (prop. delay).
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*> >The
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*> >equations used for these two are :
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*> >Z=(L/C)^(1/2)
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*> >and
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*> >Pd=(LC)^(1/2)
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*> >I guess my question has to do with Pd. How can we equate Pd to both the
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*> >above equation and the fact that the speed of light is C/((er)1/2)? Which
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*> >says that prop. delay is just a function of the dielectric constant (or the
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*> >material that light is propagating through).
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*> >Can I really reduce C, without increasing L, and thus reduce the Pd of an
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*> >interconnect? If I can't then the Pd=(LC)^(1/2) has problems. If I can then
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*> >how does it align with light's speed being just a function of the medium
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*> >it's traveling through?
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*> >
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*> >regards,
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*> >Jim
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*> >
*

*> >**** To unsubscribe from si-list or si-list-digest: send e-mail to
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*> >si-list archives are accessible at http://www.qsl.net/wb6tpu
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*> >****
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*> >
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*>
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*> ______________________________________________________
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*> **** To unsubscribe from si-list or si-list-digest: send e-mail to majordomo@silab.eng.sun.com. In the BODY of message put: UNSUBSCRIBE si-list or UNSUBSCRIBE si-list-digest, for more help, put HELP.
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-- Fred Balistreri fred@apsimtech.com**** To unsubscribe from si-list or si-list-digest: send e-mail to majordomo@silab.eng.sun.com. In the BODY of message put: UNSUBSCRIBE si-list or UNSUBSCRIBE si-list-digest, for more help, put HELP. si-list archives are accessible at http://www.qsl.net/wb6tpu ****

**Next message:**Mayer, Mike: "RE: [SI-LIST] : Bad IBIS models!"**Previous message:**Adrian Shiner: "Re: [SI-LIST] : Bad IBIS models! - Business thoughts"**In reply to:**amit agrawal: "Re: [SI-LIST] : A basic question"

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