Digital Signal Processing Reference
In-Depth Information
Signal current
Return current
D
2
Driver
Receiver
D
1
w
Figure 10-2
Driving and return currents when a signal passes over a gap in the ground
plane.
Gap width = 25 mils
50
Z
o
= 50
65
Ω
microstrip
TDR Cable
0.5 V
Probe point
TDR
0.6
0.5
0.4
0.3
0.2
0.1
0.0
0
2
4
6
8
10
12
Time, ns
Figure 10-3
Measured TDR profile of a microstrip traversing a gap in the reference
plane, showing the inductive nature of the nonideal return path.
gap in the reference plane. Notice how the gap appears inductive in the TDR
profile.
The receiver waveform will be filtered by the low-pass nature of an induc-
tor, and a portion of the signal will be delayed due to the finite time it takes
the return current to propagate around the gap. A simulation of how a nonideal
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