Differential to common mode conversion due to asymmetric ground via configurations

In this paper, the mode conversion in differential links of printed circuit boards and package structures is investigated, taking into account the ground via arrangement and trace length mismatch. The links are modeled using physics-based via and trace models that have been validated previously with full-wave methods and measurements. The very good numerical efficiency of these models allows simulations of different scenarios in minutes rather than hours compared to full-wave tools. It is shown that an asymmetric ground via configuration in the vicinity of a link end can increase the mode conversion in a comparable proportion to the trace length mismatch. The possibility to mitigate the mode conversion by compensating the trace length mismatch with asymmetric ground via configurations and vice versa is also discussed.