Thomas and Steve,

CPW differential pairs are out there. I've seen 'em and modeled for 'em and
built
'em. And your right - the "SI-List" is a great source for high end
electrical performance
discussions. Many of which are at a PhD level. : / An interesting
observation with
CPW differential pair is that the thinner the dielectric gets (with no
reference plane
at the bottom - infinite ground) the more it raises the impedance values.
(Because air
has a very low Dk of 1) Now if a plane was there of course the impedance
would
be lower due to the coupling (even mode coupling).

Cheers,

Groovy
----- Original Message -----
From: "Thomas Beneken" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Thursday, March 04, 2004 1:14 AM
Subject: Re: [TN] Impedance design question


> Hello Steve!
>
> it is possible to design the impedance of a coplanar differential pair
> without ground reference.
> Brian Wadells "Transmission Line Design Handbook", ISBN 0-89006-436-9
covers
> this. The impedance calculator of Polar Instruments
www.polarinstruments.com
> may be helpful too. Another valuable source of information is the si-list
> (Signal Integrity) on Yahoo.
>
> Regards
> Thomas
>
> > -----Original Message-----
> > From: Steve Kelly [mailto:[log in to unmask]]
> > Sent: Wednesday, March 03, 2004 8:53 PM
> > Subject: Impedance design question
> >
> >
> > Good day to all,
> >
> > I have been asked by a customer to design a single layer 100 ohm
> > differential pair circuit. I realize the impedance may be
> > highly variable
> > but I do not know how to do the calculation when there is
> > only one layer of
> > copper. If I assume there is a ground line next to the
> > differential pair do
> > I use this as the reference? Any advice or help would be
> > appreciated. Thanks
> > in advance. Steve Kelly
> >
> >
> >
> > PFC Flexible Circuits Limited
> >
> > Ph: (416) 750-8433
> >
> > Fax: (416) 750-0016
> >
> > Cell: (416) 577-8433
> >
> > E-Mail: [log in to unmask]
> >
> >
> >
> >
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