POINT TO REMEMBER
Use a Bergeron diagram to calculate the reflections on a transmission line when either
the source or load exhibits significant nonlinear I-V characteristics.
2.4.3. Effect of Rise Time on Reflections
The rise time will begin to have a significant effect on the wave shape when it becomes less
than twice the delay (TD) of the transmission line.
Figures 2.20
and
2.21
show the effect that
edge rate has on underdriven and overdriven transmission lines. Notice how significantly the
wave shape changes as the rise time exceeds twice the delay of the line. When the edge
rate exceeds twice the line delay, the reflection from the source arrives before the transition
from one state to another is complete (i.e., high-to-low or low-to-high transition).
Figure 2.20: Effect of a slow edge rate: overdriven case.
Figure 2.21: Effect of a slow edge rate: underdriven case.
2.4.4. Reflections from Reactive Loads
In real systems there are rarely cases where the loads are purely resistive. The input to a
CMOS gate, for example, tends to be capacitive. Additionally, bond wires and the lead
Summary :
Effect of Rise Time on Reflections The rise time will begin to have a significant effect on the wave shape when it becomes less than twice the delay (TD) of the transmission line.
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