How are multiple resonance frequencies calculated for the open-impedance curve for the power delivery network (PDN) of a PCB?

The open-impedance curve for the PDN of a PCB shows impedance variation with the frequency. The first resonance frequency is due to the capacitance between the power and ground planes resonating with the series loop inductance related to the spreading inductance of the power and ground planes.

Higher resonance frequencies occur when the adjacent pair of power and ground planes with a dielectric medium between them electrically form a cavity. The EM field in the cavity corresponding to the power and ground noise generated by the switching current is spread through the power and ground planes. When the spreading EM field through the cavity reaches the edges of the plane, a more significant part of the energy will bounce back, and a smaller portion of high-frequency energy will radiate. The reflection of the EM waves from the different edges of the cavity depends on the shape and geometry of the cavity.

The resonant frequency for the cavity formed by the pair of power and ground planes can be computed analytically using the formula for the resonance frequency. You can verify the same using the PowerSI, Network parameter display window.

For more information on higher resonance frequencies, look at this document on the Cadence Learning and Support Portal.

Team SimTech

Cadence Design Systems