188.8.131.52 Capacitive Coupling. When signal conductors of two circuits are near each other as shown in
Figure 6-9, a capacitance,
exists between the conductors. The value of this capacitance is a function of the
geometry of the signal lines. For parallel wires, Cc is given by (6-2).
where rc is the distance between the two lines and d is the diameter of the wires. In a similar manner, a
capacitance exists between each signal line and its return. If the signal line is parallel to its return, these
capacitances can be calculated using Equation 6-11 by replacing rc with r1 and with
(see Figure 6-9).
The interference source voltage,
produces a current flow through the mutual capacitance, Cc, between the
two signal conductors and develops an induced voltage,
in the susceptible circuit. The equivalent circuit
for Figure 6-9 is given in Figure 6-10(a) where the parallel combination of
has been replaced by
the equivalent impedance
Figure 6-9. Illustration of Capacitive Coupling