Principles of Power Integrity for PDN Design--Simplified: Robust and Cost Effective Design for High Speed Digital Products

Chapter 5. Practical Multi-Layer Ceramic Chip Capacitor Integration

5.1 Why Use Capacitors?

Capacitors are an important component in the PDN ecology because they reduce impedance in the frequency band between VRM effectiveness and the chip’s clock. The impedance of an ideal capacitor decreases inversely with frequency, as in

where

Z_C is the impedance of an ideal capacitor

ω = the angular frequency in radians per second

C = the capacitance in F

As an easy number to remember, the impedance of a 0.1 µF capacitor at 1 MHz is about 1 Ω:

Figure 5.1