Digital Signal Processing Reference
In-Depth Information
TDR
TDT
V
x
Gain = 1
[VCVS]
50
Driving line
Z
0
Z
0
50
l
x
V
Slot location
D
1
D
2
[CCCS]
+
Z
slot
Z
slot
V
x
l
x
Slot
−
G
= 1
Represents
crossing of
driver line
Figure 10-7
Equivalent circuit of a transmission line routed over a slot in the reference
plane.
TDR
0.6
0.5
0.4
Model
Measured
0.3
0.2
0.1
0.0
0
2
4
6
8
10
12
Time, ns
Figure 10-8
Comparison of a slot model compared to a measured response on a test
board.
generally not a good idea to short
V
DD
to ground, 1-nF decoupling capacitors
are used to create a high-frequency low-impedance path for the return current.
SOLUTION
Step 1:
Estimate the electrical delays of the microstrip and the slotline assum-
ing a board dielectric permittivity of 4. Since both the slotline and the microstrip
will have part of the electric fields in the air and part in the dielectric, we esti-
mate that the effective relative dielectric permittivity for both is
ε
eff
3
.
15. This
value can be calculated rigorously using the techniques outlined in Chapter 3,
=
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