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November 2005

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Subject:
From:
Eddie Rocha <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Eddie Rocha <[log in to unmask]>
Date:
Fri, 18 Nov 2005 16:59:39 -0700
Content-Type:
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text/plain (134 lines)
Wrong. The dielectric constant is a separate factor.

Thank you,
Eddie Rocha
South Bay Circuits


Eddie

All Z0 calculators have a built in "fudge factor" to make
modelled results
agree with emperical data. It is called "dielectric
constant"

Gerry


From: Eddie Rocha <[log in to unmask]>
Reply-To: TechNet E-Mail Forum <[log in to unmask]>,
             Eddie Rocha
<[log in to unmask]>
To: [log in to unmask]
Subject: Re: [TN] impedance testing
Date: Tue, 15 Nov 2005 11:53:11 -0700

I've evaluated multiple impedance calculators. I did as you
are doing, used actual x-section data with actual TDR
results and compared it to the calculators results. Some
calculators worked well with some stack-ups but not with
all types of stack-ups. A good calculator should have a
"fudge factor" that allows you to determine the best
"factor" that works for a particular stack-up. Actual data
is needed to make an impedance calculator accurate.

Thank you,
Eddie Rocha
South Bay Circuits


Hello,

If there are any impedance testing gurus out there I have a
question for
you.  We are testing an edge coupled offset strip line
coupon.  We modeled
the stack up to give us 100 ohms differential.  When we
test the coupon we
get around 130 ohms.  We have done a microsection of the
coupon and modeled
the coupon data and Polar says we should have 105 ohms,
within tolerance.
We had a 4 panel lot and it is consistent across the board.
 The coupon is
constructed correctly.  My question is, other than what I
am seeing on the
microsection should I look for to find the culprit of the
high reading?  Any
help would be great.

Jim Henderson
Colonial Circuits

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