Dude. What you are seeing is the accumulated round trip resistance of the
interconnect that you are measuring. If it is a uniform transmission line,
then you can correct the TDR profile by removing the TDR slope (which is
the resistance) and recover the true impedance.
BTW, the first time that all of us old timers looked at a TDR, we thought
the same as you.
Happy TDRing
Scott
Scott McMorrow
Consultant - R&D
Teraspeed Consulting - A Division of Samtec
16 Stormy Brook Rd
Falmouth, ME 04105
(401) 284-1827 Business
http://www.teraspeed.com
On Wed, Sep 23, 2015 at 9:10 AM, jun zhang <zhangjun5960@xxxxxxxxx> wrote:
Hi experts,
I observe a phenominon about TDR obtained by fourier transform of S11. I
notice that it gradually increases along the time axis. What does this
mean?
It seems that the impedance at each position is related to, but not
indepedant of that at other position. Characteristic impedance is unique.
so can TDR not reflect characteristic impedance? Or early time TDR still
can reflect characteristic impedance? A designcon paper mentions the
phenominon and find the cause is frequency-depend loss. So I think this is
a intrinstic drawback of TDR. It can't show accurately the impedance at
each position of the link path.
Do you agree with me?
--
best wishes,
Jun Zhang
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