Single-ended TDR Measurements
Measuring Transmission Line Impedance
7-21
We will now measure the impedance of the narrow trace using the measured
voltage along the discontinuity (vd1) of the transmission line and the following
equation:
where:
The 50 ohms is the impedance of the transmission line up to the narrow trace
and the 200 mV is the nominal height of the TDR step.
We will use the markers to measure the voltage as follows.
1 Press the SETUP Channel 1/3 key.
2 Change the
Scale
to 100.0 mV/div.
3 Press the
SETUP Marker key.
4 Press the
Mode
softkey and select TDR/TDT from the list.
5 Press the
Enter
softkey.
6 Press the
Reference
softkey to select ref plane.
7 Press the
Marker units . . .
softkey.
8 Press the
Vertical units
softkey to select Volt.
9 Press the
Done
softkey.
10 Change the
+ Position
until the + marker is over the narrow trace
discontinuity.
Before making any marker measurements, the on screen waveform must not be
clipped. Therefore, you must always adjust the channel scale until the waveform
is not clipped.
Z 50Ω
1 p+
1 p–
------------
×=
p
vd1200 mV–
200 mV
------ -------- ----------- -------- --=
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