Sue,
e is the numeric constant 2.71828...
It is found by taking the inverse ln of 1.
Buck...
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Reade, Sue
Sent: Thursday, June 23, 2005 3:32 PM
To: [log in to unmask]
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
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