Determining Effects on PDN Target Impedance Using Sigrity X

Ensuring a functional power distribution network (PDN) for chips, packages, and PCBs is a challenge for system design engineers facing increasingly difficult design targets and varying design and hardware delivery dates. A CadenceLIVE 2025 presentation is now available on demand that examines work done as part of Project Kuiper, Amazon's low Earth orbit satellite broadband network with a mission to deliver fast, reliable internet to customers and communities around the world.

Written by Ethan Koether, senior signal and power integrity engineer for Project Kuiper, along with industry experts Kristoffer Skytte, John Phillips, and Shirin Farrahi of Cadence, Abe Hartman of Oracle, Mario Rotigni, retired, and Istvan Novak of Samtec, the paper explores the spatial, frequency, and loading effects of a system on PDN target impedance requirements.

Project Goals

The presentation presents the project goals and examines two power delivery strategies: single point-of-load PDNs and PDNs feeding multiple parallel loads.

• Compare single point-of-load PDNs and PDNs feeding multiple parallel loads
• Correlate bandwidth changes from the DC source pads to IC pads on the PCB
• Present guidelines to avoid over-designing PDNs
• Understand considerations for complex, multi-load power delivery designs
• Update PDN target impedance methodology to be a function of frequency and spatial position

The required bandwidth (BW) of the PDN response depends on the supply network location. The project correlates Cadence's Sigrity X PowerSI simulations with vector network analyzer (VNA) measurements to determine bandwidth changes with major PDN components from the DC source pads to IC pads on the PCB.

The paper highlights that impedance requirements differ across the system due to spatial filtering effects.

Power integrity experts must decide whether to combine power rails or provide separate power for each device. Using two high-power processor-based server systems, the project measures and simulates power rail impedance at various PDN points. The findings offer guidelines to avoid over-designing PDNs and to understand considerations for complex multi-load power deliveries.

Conclusion

The presentation concludes that good simulation/measurement correlation was achieved for two high-power DUTs.

It highlights the spatial filtering effects of the passive PDN and their physical roots and shows that the low-frequency RC cutoff due to net capacitance and plane resistance was in the ~10kHz range. The target impedance methodology described in the presentation can be adapted and optimized for individual applications as the different noise sources and filters in a complex system PDN are considered.

You can now view Project Kuiper's CadenceLIVE presentation on demand.