Effect of mixed-reference planes on single-ended and differential links in multilayer substrates

In this paper, efficient physics-based models are used to examine diverse differential and single-ended link configurations on multilayer substrates with mixed reference planes (i.e. links running between ground and power planes). The effect of different plane assignments is studied and the results are validated with a general purpose full-wave solver. It is shown that the plane configuration affects mainly the coupling into the parallel-plate mode, and it could be either a broadband or narrowband effect depending on the link environment. Although the effect of ground vias can be appreciated with any plane configuration, the utilization of more ground planes helps to reduce the equivalent parallel-plate impedance and therefore to decrease the amount of energy coupled between the reference planes. A reduction of up to 1.8 dB of the transmission and an increase of more than 10 dB of the crosstalk could be observed at specific frequencies when the assignment of a single reference plane was changed from ground to power.