When frequencies are higher the effect of having a trace next to another becomes more pronounced and the associated losses increase. In this article I have discussed about this particular effect of having traces next to each other. I have presented some background on this phenomenon called Crosstalk and also tried to present some numerical data to show how crosstalk varies with trace spacing.

Crosstalk can be defined as unintentional coupling of noise from one circuit to another. A typical example of crosstalk would be noise coupling from a trace carrying a clock signal into a Reset signal routed next to it. In this example, when the clock switches from low to high the change in current in the clock trace creates a magnetic field around that trace. This magnetic field is a reactive field that stores energy and not a radiating field that is lossy. The magnetic field associated with the clock trace extends beyond the trace itself (for a few millimeters). Any other trace that is next to this clock trace will see an impact of the magnetic field associated with the trace. This magnetic field induces a flow of current on the trace that lies next to it. This induced current is not intentional instead it is pure noise getting coupled on to it.

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