Hi John,

D'oh.  Now I have both feet in.

What if you try the calculation as if it were a microstrip but side-ways?
The trace thickness would be the width, the trace spacing would be the
distance for the reference plane, etc..   Doing that I get about 50 ohms for
5 spacing and 4mil line with 2oz of copper including plating (Er4.2).

But, hopefully the designer will tell you that it can have the reference
trace underneath.


Regards,
Brent



-----Original Message-----
From: John Parsons [mailto:[log in to unmask]]
Sent: Thursday, November 20, 2003 12:35 PM
To: [log in to unmask]
Subject: Re: [TN] Co-planar Impedance Calculations


Brent,

That is also the problem, I am the fab house :o) but I have no experience
with the design as described to me by the designer.  The board is not layed
out yet so that is no help.  A couple of you have suggested a differential
pair (thanks Frank for the call!) but from the description the designer had
provided yesterday I don't have the reference plane on the backside.  I am
waiting to get confirmation on the design parameters from the designer.  It
was me who used the term "coplanar" to describe this design as that is what
it appeared to be from the information I had - I could be wrong.

Just for fun I ran the numbers assuming a differential pair on a regular
0.059 double sided board and I get 98.5ohm, not the 50ohm spec'd.  Diff
pairs are typically spec's for the pair not individually aren't they!?

John

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