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PHYSICAL DESIGN AND DEBUGGING
B
231732i11-10
Figure 11-10. Loaded Transmission Line
The magnitude of a reflection
is
usually represented in terms of a reflection coefficient.
This
is
illustrated in the following equations:
T
=.
V,lVi
= Reflected voltage/Incident voltage
T
source
=
(Zsource
-
Zo)/(Zsource
+
Zo)
Reflection voltage Vr
is
given
by
Vi' the voltage incident at the point of the reflection,
and the reflection coefficient.
The model transmission line can now be completed.
In
Figure 11-10, the voltage seen
at
.
point A
is
given
by
the following equation:
This voltage
Va
enters the transmission line
at
"A"
and appears at
"B"
delayed by
tpd'
Vb
=
Va
(t
-xlv)
H(t-
xlv)
where x = distance along the transmission line from point
"A"
and H(t)'
is
the
unit stop
function. The waveform encounters the
load~,
and this may cause reflection. The
reflected wave enters the transmission line at
"B"
and appears
at
point
"A"
after time
delay
(~d):
11-13