Intel Embedded Intel486 Hardware Reference Manual page 298

EMBEDDED Intel486™ PROCESSOR HARDWARE REFERENCE MANUAL
The amount of reflection voltage can be easily calculated.
ing reflections.
The magnitude of a reflection is usually represented in terms of a reflection coefficient. This is
illustrated in the following equations:
t = v /v = Reflected voltage/Incident voltage
r i
t = t = (Z – Z )/ (Z + Z
L Load L 0 L
t = t = (Z – Z )/ (Z
S Source S 0
Reflection voltage v is given by v
r
flection coefficient.
The model transmission line can now be completed. In
is given by the following equation:
V = V * Z /(Z + Z )
A S 0 0 S
This voltage V enters the transmission line at "A" and appears at "B" delayed by t
A
V = V (t – x/v) H(t – x/v)
B A
where x = distance along the transmission line from point "A" and H(t) is the unit step function.
The waveform encounters the load Z
the transmission line at "B" and appears at point "A" after time delay (t
V = t ·V
r1 L B
This phenomenon continues infinitely, but it is negligible after 3 or 4 reflections. Hence:
V = t ·V
r2 S r1
Each reflected waveform is treated as a separate source that is independent of the reflection co-
efficient at that point and the incident waveform. Thus the waveform from any point and on the
transmission line and at any given time is as follows:
V(x,t) = Z /(Z + Z ) { [V
0 0 S
t [V (t-(2L-x)/v)] [H(t-(2L-x)/v)]
L S
t t [V (t-(2L + x)/v)] [H(t-(2L + x)/v)]
L S S
2
t t [V (t-(4L-x)/v)] [H(t-(4L-x)/v)]
1 S S
2 2
t t [V (t - (4L+x)/v)] [H(t(4L+x)/v)]
1 S S
+.............}
Each reflection is added to the total voltage through the unit step function H(t). The above equa-
tion can be rewritten as follows:
10-14
)
0
+ Z )
S 0
, the voltage incident at the point of the reflection, and the re-
i
, and this may cause reflection. The reflected wave enters
L
(t-x/v)H(t-x/v)]
S
Figure 10-10 shows a system exhibit-
Figure 10-10, the voltage seen at point A
):
pd
.
pd