32 The PCB Design Magazine • February 2015
Medium frequency 1 or 2 GHz narrow trac-
es, impedance:
At high frequencies, 3 GHz and above, in-
sertion loss is significant:
In conclusion, when looking at transmis-
sion line measurements and specifying trans-
mission line characteristics, you should ensure
that if you are working with narrow traces and
thin copper and your frequencies are not yet
high enough to worry about dielectric losses,
you should take a look at your TDR waveforms
for a significant slope in the measurement area.
Consider specifying the measurement of in-
stantaneous impedance by using Launch Point
Extrapolation.
PCBDESIgn
References
1. "Deduce" definition: www.vocabulary.com.
2. Luis Navarro, Timothy Chairet, Eugene
Mayevskiy, "Application of Launch Point Ex-
trapolation Technique to Measure Characteris-
tic Impedance of High-Frequency Cables with
TDR," DesignCon 2009.
3. Lossy Traces: Where and How to use Loss
Compensation, Polar Instruments Application
Note AP156.
4. Measuring Impedance on Thin Traces
with Launch Point Extrapolation, Polar Instru-
ments Application Note AP8505.
Figure 3: TDr trace with lPe and sloping impedance result.
Martyn Gaudion is CeO of
Polar Instruments.
To contact him, click here.
I
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: InCIDEnT, InSTAnTAnEOUS, IMPEDAnCE continues
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