Reference
28 80E00 ElectricalSampling Modules User Manual
The reflections that a TDR displays and measures are caus ed by changes in the
impedance of the path of the step (circuit board, cable, or integrated circuit). Any
significant change in impedance wil l cause a reflection. As an example, if an
open solder connectionexists on a circuit board, you can see that change with
TDR. TDR also displays changesin the conductor resistance. For example, if
there is corrosionin a joint and there is high resistance at that point, this is seen
by a TDR. TDR also displays changes in cap acitance.
If you think of theTDR display in termsof bumps and dips, it tends to make
interpretationa lot easier. A bump (upward deflection) indicates a higher-imped-
ance event, such as an open (see Figure 13) or a reduction in lin ew idth (see
Figure 12). A dip (downward defl ection) indicates a lower-impedance event,
such as a short (see Figure 14) or an increasein conductor width (see Figure 12).
The time location of the high-impedanceevent or low-impedance event as well
as the deltatimes is displayed on screen.
Open
Connector
Capacitive
discontinuity
Inductive
discontinuity
Figure13: TDRwaveform of microstr ipin Figure 12
Cause of Reflections