[SI-LIST] Re: Impedance measurement
- From: "Wenzel Robert-r37657" <Robert.Wenzel@xxxxxxxxxxxxx>
- To: <si-list@xxxxxxxxxxxxx>
- Date: Thu, 1 Nov 2007 13:37:08 -0700
Bharath,
Setting aside the instrumentation and other potentially severe
complications aspects, I have some basic theoretical "lumped, low
frequency" extraction formulas for a 2-wire line to get you started,
work well for uniform line or gives an "average". Things can be much
more matrix complex for your 3-wire line.
L=3Dimag(Zsc)/w
R=3Dreal(Zsc)
G=3Dreal(1/Zoc)
C=3Dimag(1/Zoc)/w
zosimp=3Dsqrt(L/C)
zocmplx=3Dsqrt((R+jwL)/(G+jwC))
where w is omega. The calculator sqrt function needs to handle complex
#'s for zocmplx and choose correct sign. Imag(zocmplx) is most often
negative I believe.
Best Regards,
Rob
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On Behalf Of Bharathkumar Raju
Sent: Thursday, November 01, 2007 7:46 AM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Impedance measurement
Dear All,
Is it possible to measure the impedance of USB D+ & D- signal
traces of an unassembled PCBA, using HP 4249 impedance analyser? One end
of the traces are left open and I measure the impedance across the pair
at the other end. By measuring Zsc & Zoc I hope we can calculate the CI.
Measuring with other end of the traces connected together (Zsc)
seem to be easy and we get consistant results. What are the issues in
using HP 4249 or similar impedance analysers in measuring impedance of
open ended untermintaed traces (Zoc)? I request the experts to guide me
in measuring Zoc accurately using impedance analysers.
Bharath
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