Digital Signal Processing Reference
In-Depth Information
v
out
Slope =
−
1
V
CC
v
OH,
min
Slope =
1
−
v
OL,
max
V
SS
v
in
V
SS
v
IH,max
v
IH,
min
V
CC
Figure 4-14
Receiver transfer characteristic and switching thresholds.
on the signal that causes an excursion back below
v
IL
will cause erroneous
switching (Figure 4-15). It is the job of the system designer to make sure that
this does not happen.
Refer to Chapter 11 for additional details on the operation of receivers for
high-speed links.
Qualitative Description
Before developing a quantitative treatment of
crosstalk-induced noise, we describe the behavior qualitatively by looking at the
propagation of the aggressor and coupled noise wave. From our discussion of
mutual inductance and capacitance it is apparent that energy is coupled from one
line to another only during signal transitions (i.e., the rising and falling edges).
Subsequently, we look at the propagation of a rising edge on the aggressor line.
Figure 4-16 shows a pair of coupled lines terminated at both ends that represent
a typical system. As the incident wave on the aggressor line is launched, it imme-
diately begins coupling over to the victim line through the mutual capacitance
and inductance. Current that couples through the mutual capacitance (
i
C
) splits
into forward-traveling (
i
f
) and backward-traveling (
i
b
) components in the victim
line, as shown in Figure 4-17. Current that couples through the mutual inductance
(
i
L
) travels back toward the source end. As a result, we have a forward-coupled
wave that is a function of the difference between the capacitively coupled current
and the inductively coupled current. Since it is based on the difference between
capacitive and inductive coupling, the amplitude may have the same polarity as
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