Issue link: https://iconnect007.uberflip.com/i/1276973
38 DESIGN007 MAGAZINE I AUGUST 2020 resonance. By the time we properly add up all series and parallel inductances, it comes out around 160 pH. The antiresonance with the 10-nF Cdie value comes out close to 100 MHz, where the split antiresonance peak happens. We still need to understand where the two extra resonances—Notch 4 and Peak 5—come from. To get the answer, we need to go back to Figure 4 and check what happens with the parameters that we did not fill out. On the left, there are two parameters we left empty: paral- lel capacitance and parallel resistance. What happens if we explicitly set the body capaci- tance to zero? The result is shown in Figure 5. Notch 4 and Peak 5 disappeared, but the rest remained practically unchanged. Now, the resonance pattern makes sense, but there is still something happening. Why do we have 5-mOhm impedance at low frequencies, when the circuit calls out only 1 mOhm and three times 0.1-mOhm resistor values in the series path, altogether 1.3-mOhm series resis- tance? We need to look at the definitions of the inductors. The definition of inductor attributes is shown in Figure 6 [5] . In the same way we did it for the capaci- tors, we can call up the parameter-entry win- dows for the inductors as well. In Figure 7, we see two parasitic components listed: series resistance and parallel capacitance. We also see a note at the bottom of the left window. There is a 1-mOhm default value for the series resistance. This means if we do not make an Figure 5: Impedance magnitude and phase of the simple PDN showed in Figure 1, but all parallel body capacitance is set to zero. Figure 6: Equivalent circuit of inductor parasitics and attribute list.