FreeLists / si-list / [SI-LIST] Re: Impedance without a reference plane

[nagaraj <nagaup1@xxxxxxxxx>]

Bharath,
The characteristic impedance is given by,

Z0 = sqrt (L/C) , where L inductance/sq-inch and C Capacitance/sq-in

If we look at the formula for C = EA/D  E- dielectric constant, A Area of the 
plate and D spacing between the plates.

In your case the D  means is infinity hence your impedance is also infinity ( 
directly proportional). In practical, the impedance is of large value. 

If no reference place then signal might have used a reference trace for the 
signal to complete. So it becomes a two wire system as such. 

Hope this is of some help.
Thanks,
Nagaraj.

Bharathkumar Raju <bharathrajupcb@xxxxxxxxxxx> wrote: Hi,
            Have any one come across the situation where you need to simulate, 
calculate, measure, the characetristic impedance without a reference plane.
            I have a design where I need to decide upon the impedance of an 
isoalted trace (no other traces in the neighbourhood) of about 25 mil width 
withour any reference plane underneath.
             You inputs, sugestions will be of great value.
  Bharath
     
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