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| Date: | Thu, 23 Jun 2005 17:08:25 -0400 |
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Sue
"e" is an irrational number just as pi (3.14....). The mathematical definition of e is (1+1/n)**(n) as n approaches infinity. There is not an exact value, but 2.718 is usually close enough. Mathematicians consider it to be the second most important irrational number.
Fortunately, very close to you over on Hillsboro Street at the world's foremost technical institute, the math department has a display (or use to) with the value of e to 1000 places. <>
Best regards
Lee
J. L. Parker Ph.D.
JLP Consultants LLC
(804) 779 3389
----- Original Message -----
From: Reade, Sue<mailto:[log in to unmask]>
To: [log in to unmask]<mailto:[log in to unmask]>
Sent: Thursday, June 23, 2005 3:31 PM
Subject: [TN] Pcb impedance models
I'm educating myself and need some assistance understanding the absolute
basics of the impedance formula for E'r (relative permittivity).
Below is the basic formula for Zo in embedded stripline
87 [5.98H]
----------- * LN -------------
sqrt E'r+1.41 [ 0.8W+T ]
where
E'r = Er(1-e(-1.55H1')
--------------
H
Er = material defined relative permittivity
H = the distance from the reference plane to the signal line
H' = the distance from the reference plane to the top of the dielectric
My question: what does the variable e represent in the calculation for
E'r?
Sue Reade
CAD Engineer
[log in to unmask]<mailto:[log in to unmask]>
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Morrisville, NC 27560
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