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March 2005

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Subject:
From:
Judy Brown <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Judy Brown <[log in to unmask]>
Date:
Tue, 29 Mar 2005 15:28:31 -0800
Content-Type:
text/plain
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text/plain (116 lines)
Steve,
        Try the website for Rogers, they have an impedance calculator.
www.rogers.com. 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Mcmaster, Michael
Sent: Friday, March 18, 2005 4:56 PM
To: [log in to unmask]
Subject: Re: [TN] Impedance calculations

In addition to possible calculation errors, you also need to be
concerned
with measurement error.  Most TDR techniques calibrate at 50 Ohms, you
are
trying to measure half of that.  Measurement speed can also be more
critical.  Since the coax line connecting the DUT to the scope is 50
Ohms,
if you don't measure at high enough speed or with a long enough
transmission
line, you will see a shift towards the cable impedance.

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Kelly
Sent: Friday, March 18, 2005 3:23 PM
To: [log in to unmask]
Subject: [TN] Impedance calculations

Good late Friday afternoon to all,

I am trying to understand what happens to my impedance calculations when
we
start going below 35 ohms. When I use Ultracad or do the calculations by
hand I get the following results:

Copper finished - .0014 (1 oz.)

Dk - 3.5 (it is a flex)

h- .003

Line width to get 25 ohms (surface microstrip) - .007 to .008.

We wound up building this part with a line width of .016 and the TDR
results
measured by both myself and my customer are 29-30 ohms.

When I use the calculator from Txline it says the line width should be
.016.




Thanks in advance. Regards 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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