The examples in this paper shows how the addition of cavity elements, such as a voltage regulator module (VRM), decoupling capacitors, and stitching vias, influence the impedance of a cavity.
Different ways to lower the PDN impedance profile of the cavity
The addition of a VRM, decoupling capacitors, and stitching vias lowered the impedance profile of the cavity at different frequency ranges
Decreasing the thickness of the cavity further lowered its impedance, to the extent that the impedance of a thin cavity was not affected by the location of a capacitor.
It is very important to make the PDN cavity as transparent as possible for signals' return paths.
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