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42 The PCB Design Magazine • January 2016 MHz. A second peak is added at one and half decade higher, at 3.16 MHz, also with exactly 100 mOhm peak value. The third peak is added one and half decade below the first resonance, at 3.16 kHz. Finally a fourth peak is added at one and half decade above the second peak, at 100 MHz. Note that at very low and very high frequencies the impedance settles at 1 mOhm, 1% of the peak value. The one-and-a-half decade separation between the peaks allows the imped- ance magnitude to drop substantially in be- tween, close to the 1 mOhm asymptote values. Figure 6 shows the step response of each of the four cases. Note that the horizontal scale is logarithmic to accommodate the ringing of widely differing frequencies. All four cases have impedance profiles not exceeding a 100-mOhm target value, so by ignoring the non-flatness of quiet power HoW To DESIgN A PDN FoR THE WoRST-CASE SCENARIo Figure 6a: Step response with one 100 mohm peak. Worst-case transient noise from the reverse pulse technique is 120 mVpp for each ampere of excitation. Figure 6b: Step response with two 100 mohm peaks. Worst-case transient noise from the reverse pulse technique is 234 mVpp for each ampere of excitation. Figure 6c: Step response with three 100 mohm peaks. Worst-case transient noise from the reverse pulse technique is 346 mVpp for each ampere of excitation. Figure 6d: Step response with four 100 mohm peaks. Worst-case transient noise from the reverse pulse technique is 453 mVpp for each ampere of excitation.