Crosstalk and Mode Conversion in Adjacent Differential Lines

In this paper, the concepts of weak coupling and weak imbalance are exploited to investigate crosstalk and mode conversion occurring in perfectly balanced differential lines (DLs) due to proximity with other DLs printed on the same PCB substrate. Approximate modal circuits are derived, where the aforementioned phenomena are accounted for by the use of distributed voltage and current sources. This allows evidencing the relevant parameters at the basis of these undesired phenomena, which may significantly degrade DL performance in terms of emission and immunity properties as well as signal integrity. Accuracy of the proposed model, preliminary validated versus exact solution of transmission line equations, is eventually assessed through vector network analyzer measurements carried out on a PCB sample.