Reference
80E00 ElectricalSampling Modules User Manual 23Overview Controlelem ents& resourcesTotake a TDR measurement (cont.)
Setother TDR
parameters
7. Adjust the VERTICAL SCALE (500 mρ/div in this
example) and HORIZONTALSCALE (2 ns/div in this
example)to show a trace similar to thatshown. Leave at
least one division of baseline trace to the left of the
firstrise.
Thef irst rise of this waveform is the incident TDR step
leaving the sampling module; the second rise is the
reflection of the step returning from the end of the cable.
Foryour device undertest (DUT),you may need to
adjust the Horizontal SCALE, POSITION, and
Referencet o display the reflections from your DUT near
the left of the graticule.
Tolocate reflections from your DUT, disconnect your
probeor cable at t he DUT and look for the reflection
from the open end of the probe or cable.
Assuming the line to be tested is an open-end microstrip
ona ci rcuit board and that your probe orcabl e is now
connected to the line, you will see the new open
reflection to the right according to the length of the line.
Theremay be a vi sible disturbance where the
connection is made to the board (for example, see
Figure12 on page 27). The area between t he entry to
the boardand t he open reflection at the end of the board
is the target area for your TDR measurements. Adjust
VerticalSCALE, Vertical POSITION, Horizontal SCALE,
andHorizont al POSITION as necessary for a good
quality display of the measurement area.
ρ
ρ
Reflectionf
r
om
openend of cable
Incident
TDRstep
Changing TDR
graticuleuni ts
8. Theuni ts of measure commonly used in TDR are units
of rho(ρ), measured on the verti cal axis. Youcan
changet he measurement units by using the ACQ Units
selector in the TDR Setups dialog box.
9. Pressthe SETUP DI ALOGS button, and select the TDR
tab.
10. Select either Vfor Volts,ρfor rho, or Ωfor ohm s. Enable
TDR
TDRtab