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26 The challenge for the PDN engineer is to get that 48 volts to 1 volt with variable current demands that can range from high to low. The traditional way of doing this is to use switched capacitor converters (SCCs) to step down from 48 volts to 12 volts, and then step down further to about 1 volt, and then have large banks of capacitors around the processor core capable of handling the variable power demands. That works, but it takes up a lot of space, and passive components, such as capacitors, have not achieved the same kind of efficiency and density improvements as silicon-based components. Processor cores are shrinking faster than the passive components in the PDNs that power them. Engineers are coming up with nontraditional approaches to solve this problem. One example involves the use of switched tank converters (STCs). STCs are made by using resonant inductors with resonant capacitors to create resonant tanks that replace DC flying capacitors in an SCC. This approach is a highly efficient method of DC-DC power conversion that takes up much less space than traditional SCC methods. Having smaller, denser power conversion makes it possible to put power delivery much closer to the processor core, which in turn enables faster power switching to accommodate rapid changes in power consumption in the processor core, reducing the number of capacitors needed to supply the processor core with the power it needs. The STC approach suggests that designing smaller, more efficient PDNs capable of faster switching is not just a matter of shrinking an old design and adding many tiny capacitors until everything works. It requires carefully selecting passive components. To do that, you must have a deep understanding of impedance levels across the entire operating frequency range, the power those components must handle at different frequencies, and the characteristics of the passive components themselves. '' Designing smaller, more efficient PDNs capable of faster switching is not just a matter of shrinking an old design and adding many tiny capacitors until everything works."

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