# RE: [SI-LIST] : A basic question

From: Clewell, Craig W ([email protected])
Date: Fri Mar 17 2000 - 05:39:10 PST

Jim,

If you want to relate the two try this.

Vp = c/(Er)^1/2 (Phase Velocity)
Pd = length/Vp (Delay)

The length of the signal path is also respnsible for the delay. The above
relationship takes this into account. A lower dielectric, and/or a shorter
path length will reduce the delay. If you reduce the length you are also
reducing the inductance.

Have a good weekend!
~Craig~

-----Original Message-----
From: Peterson, James F (FL51) [mailto:[email protected]]
Sent: Friday, March 17, 2000 8:01 AM
To: '[email protected]'
Subject: [SI-LIST] : A basic question

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?

regards,
Jim

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