Physical characteristics of the PCB, like component mounting inductance, plane spreading inductance, via and BGA ball inductance, along with voltage regulator module (VRM) characteristics also contribute to the impedance profile. There are always parasitic elements known as equivalent series inductance (ESL) and equivalent series resistance (ESR). In the real world, there is no such thing as an ideal capacitor. Practically this is achieved with a network of capacitors with different values connected to the respective power planes as shown in Figure 1.įigure 1 A simplified model of a typical PDN courtesy. When designing a power distribution network (PDN) in the PI world, we are mostly interested in engineering a flat impedance below a target impedance from DC to the highest frequency components of the transient current. Traditionally the PI world lives in the frequency domain while the SI world lives in the time domain. One such collision occurs when we refer to characteristic impedance, Z 0. Signal and power integrity (SI/PI) simulations, measurements, and analysis usually live in two different worlds, but occasionally these worlds collide. Originally published Signal Integrity Journal, February 23, 2021
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