10-13
PHYSICAL DESIGN AND SYSTEM DEBUGGING
At lower edge rates, the effects of these reflections are not severe. However at higher edge rates,
the rise time of the signal is short with respect to the propagation delay. Thus it can cause prob-
lems as shown in Figure 10-9.
Figure 10-9. Overshoot and Undershoot Effects
Figure 10-10. Loaded Transmission Line
Overshoot is caused by poor matching, which occurs when the voltage level exceeds the maxi-
mum (upper) limit of the output voltage. Undershoot occurs when the level exceeds the minimum
(lower) limit. These conditions can cause excess current on the input gates which results in per-
manent damage to the device.
A5285-02
Voltage
Undershoot
Time
Overshoot
Expected Output Signal
Output Signal Received
Z
L
B
Z
0
C
0
.
X
A
Z
S
V
S
L
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