Chapter 2. Essential Principles of Impedance for PDN Design
2.1 Why Do We Care About Impedance?
Ultimately, a PDN is acceptable if it provides a voltage to the chips that is within the specified range: an average value with some AC ripple. Unfortunately, whether this voltage stays at an acceptable level is based on not only the PDN design but also on the behavior of the various chips in the system: what functions they perform and the frequency spectrum of current they draw.
The voltage measured at a location on the circuit board might be acceptable while running a particular section of code. However, no guarantee exists that running other microcode will produce acceptable results. Voltage measured on the pads of a chip often has more noise than ...