5
These expressions are valid for loose couplings (KB < 0.25). It is clear that crosstalk can be decreased by
decreasing mutual coupling Cij and Lij, or by increasing the coupling to ground.
Figure 3 indicates two signal lines in close proximity that are capacitively coupled (CM) and inductively
coupled (LM). Both lines have the same characteristic impedance, Z0, and are fully terminated to avoid
reflections. One line is "active" and transmits a pulse, while the other is "passive".
At the source end of the passive line, the current due to CM and the current due to LM are additive.
These summed currents produce a voltage drop of the same polarity as the source voltage, termed "Near
End" or "Backward" crosstalk (it travels the opposite direction to the source pulse). At the far end of the
passive line, the current due to CM and the current due to LM are of opposite polarity producing "Far End"
or "Forward" crosstalk.
Figure 3. Two parallel coupled transmission lines. L=length.
4
1
* ) (
j ii
j
jj ii
ij
ij
Lj L
Li
C C
C
KB
2
* ) (
jj ii
j ii
j ii
j
jj ii
ij
ij
C C
Lj L
Lj L
Li
C C
C
KF
