CROSSTALK

When the several lines come close to each together, the current flowing across one line may have the effect of causing current flow in one or more than one adjacent lines. This may be due to the characteristics of capacitance between the two lines or there may be effect of inductance. The effect is refers to as crosstalk, and this effect often occurs in multi cored cables and it also occurred in the ribbon cables that are used for connecting computers to peripheral devices. This effect may be eliminated in multi-cored cables by way of having each of the cores enclosed in a separate earthed shield, although due to this reason the cable is considerably more expensive.

By connecting two alternate lines to ground somewhat enables us to reduce crosstalk in ribbon cables. The crosstalk process also happens between adjacent tracks on the same circuit boards, especially when the tracks run side-by-side for substantial distances. This is normally avoided by running grounded tracks between the active ones. The magnitude of the current induced by a magnetic field is directly proportional to the variation rate of the magnetic flux. This in turn is proportional to the rate of change of the current generating the field. So here we come to know that, the induced crosstalk is more serious at higher frequency level.

The effect is the identical as for the capacitative crosstalk because there is decrease incapacitance with frequency and high-frequency signals pass more gladly through the capacitative barrier.

The pulses in data signaling at high rates have very rapid rise-times, and all of these result in the most serious crosstalk problems. Spikes several volts high might be induced on an adjacent line at the beginning and end of each pulse. The effect can entirely disrupt the signal that is on the adjacent line. We can adjust the rise time with many kinds of line driver so that it is no more rapid than necessary, and as a result the effect of crosstalk is minimized.