The Effect of Power Distribution Network (PDN) Elements On Impedance

In this paper, we continue our discussion of the power distribution network or PDN. As discussed in the paper ‘Concepts of Power Integrity: Controlling Impedance across a Bare Cavity,’ a low-impedance PDN is critical for maintaining adequate current delivery to the receiver and, ultimately, for ensuring the proper performance of a printed circuit board (PCB).

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 Power Distribution Network 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.
• Making the PDN cavity as transparent as possible for signals' return paths.

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