Digital Signal Processing Reference
In-Depth Information
reflection chart [1, 6, 7] will be used manage the sums and to show the timing and
amplitude of the reflections.
We begin by using the voltage divider principle to determine that the driver
launches 1.67V down the line. This is the incident voltage,
V
i
.
From (11.3) we find the reflection coefficient at the driver end of the line is
10
RZ
RZ
−
−
50
g
o
ρ
=
=
= −
0.67
, and from Table 11.1,
ρ
l
is +1.
g
+
10
+
50
g
o
We are now ready to construct the reflection chart shown in Figure 11.7.
The voltages present at the generator end of the line are recorded on the left
side of the chart, and the load end voltages are recorded on the right side. Time
increases vertically downward with the zigzagging lines representing the reflection
bouncing between the two ends. Creating a reflection chart for the voltage wave is
described here, but the method for the current chart is the same.
The chart is filled in as follows:
1. At
t
0 the 1.67V incident wave found with the voltage divider principle
is launched.
=
Generator
end
Load
end
t
= 0
1.67V launched
t
r
= 2 ns
= +1
l
V
(1.67)
(1.67)
3.34V
=
+
=
t
t
r
4 ns
0.67
=
=−
g
V
(1.67)
( 1.12)
0.55V
=
+
−
=
t
t
= 6 ns
V
=−
( 1.12)
+−
( 1.12)
= −
2.24V
t
t
= 8 ns
V
=−
( 1.12)
+
(0.75)
= −
0.37V
t
t
= 10 ns
Figure 11.7
Refl ection chart illustrating results from Figure 11.6. The load is separated from the
generator by an electrical distance of 2 ns. Generator voltages appear on the left and load voltages
appear on the right.
