Modeling and simulation of coupled transmission line interconnects over a noisy reference plane

Limitations in using conventional coupled transmission line simulators to model signal propagation over a noisy reference plane are explained. A distributed lumped element circuit model including reference plane parasitics and associated coupling (to signal conductors) parasitics is developed, and verified using SPICE simulations. Inductance and capacitance per-unit-length [pul] matrix elements are calculated using detailed two-dimensional parasitic extractors, and the partial inductance concept. Results using this model were compared with conventional “isolated” (switching noise isolated) coupled transmission line simulations. Significant differences were found. Package pin placement on the reference plane, and its impact on overall noise characteristics are analyzed