Impact of Voltage Regulator Modules on Power Distribution Network Impedance

The voltage regulator module (VRM) impacts the power distribution network (PDN) impedance in the lowfrequency range. The effect of VRM is essential for reliable PDN analysis and simulation. However, the existing VRM models for power integrity (PI) simulation lack an in-depth understanding of the effect of the feedback control in the VRM. In this paper, the impact of the VRM control loop on the PDN impedance is investigated. The relationship between the VRM output impedance and the PDN impedance at the IC input pin is derived. The output impedance of a VRM is analyzed using small signal analysis. Eventually, the PDN impedance considering the VRM is obtained. The analysis method was validated on a commercial VRM. The proposed method can be used to calculate the PDN impedance with the VRM on in the PDN design stage.