Analysis of Switching Voltage Regulator Noise Coupling to Signal Via Using a Novel Simulation Approach

Switching voltage regulators (VR) are widely used in modern server systems. The fast transition edges of voltage and current in a switching VR generates significant power noise. The frequency of noise at as high as a few hundreds of MHz can easily couple to adjacent high-speed traces or signal vias causing its performance degradation. This paper studies a real-world problem due to Via-to-Via noise coupling in a server system. The coupling mechanism can be interpreted as mutual inductive and capacitive coupling. Board cutout's S-parameters model extraction are obtained using full wave simulations. Transfer impedance is analyzed, and inductive coupling proved to be the dominant path in a Via-to-Via case. A novel 4-port setup is adopted in time domain simulation to quickly obtain the noise coupling results, without the need of complicated VR model, which saves a lot of time. Proposed mitigation methods are verified through this simulation approach before the design spin and are correlated with experimental data.