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November 2003

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Subject:
From:
John Parsons <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Thu, 20 Nov 2003 09:35:17 -0800
Content-Type:
text/plain
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text/plain (92 lines)
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

> -----Original Message-----
> From: Alcorn, Brent [mailto:[log in to unmask]]
> Sent: November 20, 2003 9:14 AM
> To: 'John Parsons'; TechNet E-Mail Forum.
> Subject: RE: [TN] Co-planar Impedance Calculations
>
>
>
> Hi John,
>
> I opened my mouth too soon... I missed the part that is was coplanar.
>
> I would suggest contacting the fab house you are going to use.  Most
> reputable fab houses have engineering staff that do the calculations and
> will provide the data to you. The calculators only give you part of the
> equation anyway especially on a 2 layer card.
>
> Does the reference signal have to be coplanar?  I wouldn't think
> it wouldn't
> give much of a reference.
>
> Regards,
> Brent
>
>
>
> -----Original Message-----
> From: John Parsons [mailto:[log in to unmask]]
> Sent: Thursday, November 20, 2003 11:48 AM
> To: TechNet E-Mail Forum.; Alcorn, Brent
> Subject: RE: [TN] Co-planar Impedance Calculations
>
>
> Brent,
>
> Yes, from what I understand this is correct but that is my
> problem, I don't
> have a calculator to model this design to verify the parameters.
> I could do
> as Jason has suggested and just build to "spec" but I don't know if a
> complete material spec has been provided.  I am enquiring as to this.  I
> would however still like to understand the design, especially when the
> designer has come to us to help him understand and verify the design.
>
> Thanks to all for the input - keep it coming.
>
> John
>
> > -----Original Message-----
> > From: TechNet [mailto:[log in to unmask]]On Behalf Of Alcorn, Brent
> > Sent: November 20, 2003 8:36 AM
> > To: [log in to unmask]
> > Subject: Re: [TN] Co-planar Impedance Calculations
> >
> >
> > Perhaps the "other" trace is the reference?  Although ideally,I
> > believe, you would want the reference to be about 2x the width of the
> > signal trace. Perhaps the design dictates that each signal has its own
> > reference??
> >
> > Just my 2cents or 1.4 CDN.
> > Brent
>
>

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