Modeling and measurement of mode-conversion and frequency dependent loss in high-speed serial interconnection

Abstract

Modeling and measurement of mode-conversion and frequency dependent loss in high-speed serial interconnection have been studied. We proposed the modeling algorithm and new mixed-mode s-parameter to model differential line considering mode-conversion using 2-port VNA. The proposed modeling procedure is based on 2-port s-parameter measurement using 2-port VNA. But, it is hard to measure differential line using 2-port VNA, because differential line is 4-port network. However, if open and short patterned differential lines are measured and we use the proposed mixed-mode s-parameter, it is possible to extract all of differential-mode, common-mode parameters considering mode-conversion and frequency dependent loss. Using the proposed modeling procedure, we have successfully modeled, measured, and studied three types of unbalanced differential line structures representing typical cases structures in practical PCB designs. The unbalanced structures for this study include trace width mismatch and ground proximity mismatch. From the measurements and the analysis, it is verified that the line imbalance and the loss are well reflected by the proposed model. The proposed model and the model parameters were successfully verified by a lattice diagram analysis, by DTC conversion TDR and TDT measurements and by eye-diagrams. We simulated and measured differential-mode signals converted from common-mode SSN between power/ground planes. Since the proposed model can consider both DTC and CTD mode-conversion effect. The differential-mode signals converted from common-mode SSN can be estimated accurately. The proposed model can be effectively used to estimate the impact on signal integrity by the line imbalance resulting from unwanted process uniformity variation or unavoidable design circumstances. In addition, it can also be used to minimize the risk at an initial PCB design. Furthermore, the model is helpful to understand and solve the source of signal integrity problems and to p...