Digital Signal Processing Reference
In-Depth Information
R
L
R
L
Separation
āsā
FEXT
voltage
L
s
L
m
L
s
Aggressor
trace
Victim
trace
C
m
C
s
C
s
R
L
R
L
NEXT
voltage
Figure 10.1
Electric and magnetic coupling between traces transfer energy from the aggressor to
victim trace. The mutual capacitance (
C
m
) represents the electric coupling, and mutual inductance
(
L
m
) represents the magnetic coupling. (
From:
[7]. Used with permission.)
I
C
I
C
FEXT = (
I
IR
Victim
ā
cLL
NEXT = (
I
+
IR
c
L
L
I
L
I
L
R
L
=
Z
o
R
L
=
Z
o
C
m
L
m
I
s
I
s
R
L
=
Z
o
V
L
=
R
L
I
s
Culprit
V
s
I
s
R
L
=
Z
o
dv
dt
Length = l
Delay = tpd
Figure 10.2
Mutual capacitance and inductance cause current to fl ow in the tiny portion of the victim
trace shown. (
From:
[7]. Used with permission.)
The lines are considered to be loosely coupled in this way when the coupling is
under 25% [3].
The result is that the current from the mutual inductance flows back toward
the source, while the current from the mutual capacitance flows in both directions.
The currents combine to create a total noise current at each end of the victim.
At the near end the noise current is the sum of the two and creates the near-end
crosstalk voltage (NEXT). At the far end the two noise currents flow in opposite
directions, making the total the difference between the current coupled by the mu-
tual capacitance and the current coupled by the mutual inductance. The combined
