RE: [SI-LIST] : A basic question

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From: Peterson, James F (FL51) (james.f.peterson@honeywell.com)
Date: Fri Mar 17 2000 - 05:51:24 PST


Can we change C without changing the dielectric constant? Let's say we
change the thickness between conductor and ground plane. We haven't changed
L (I don't think) and we haven't changed the dielectric material, but we
have changed C. So, did Pd change? If it did, then how did we do it without
changing the dielectric constant?

-----Original Message-----
From: Zabinski, Patrick J. [mailto:zabinski.patrick@mayo.edu]
Sent: Friday, March 17, 2000 8:32 AM
To: si-list@silab.eng.sun.com
Subject: RE: [SI-LIST] : A basic question

Jim,

Z & Pd are related as you state.

Can C be changed without effecting L? Sure. Simply
change the dielectric. As long as you keep the same
physical geometries and only change the dielectric constant,
C will change with no change in L.

In fact, many of the older EM tools (still some today) relied
on the Z and Pd relationship. Essentially, it's easier
to determine C (F/m) for a line than it is L. So,
after the tool would compute C, it would use the Z and
Pd relationship to determine L

        L = Er/(Co^2 * C)

        where
        L = H/m
        Co = speed of light = 3e8 m/s
        C = F/m

Pat

Pat

> SI List:
>
> I have a question about the relationship between Z and Pd
> (prop. delay). The
> equations used for these two are :
> Z=(L/C)^(1/2)
> and
> Pd=(LC)^(1/2)
> I guess my question has to do with Pd. How can we equate Pd
> to both the
> above equation and the fact that the speed of light is
> C/((er)1/2)? Which
> says that prop. delay is just a function of the dielectric
> constant (or the
> material that light is propagating through).
> Can I really reduce C, without increasing L, and thus reduce
> the Pd of an
> interconnect? If I can't then the Pd=(LC)^(1/2) has problems.
> If I can then
> how does it align with light's speed being just a function of
> the medium
> it's traveling through?
>
>

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