What is Power Integrity and Power Distribution Network?


Power integrity is one of the mind-boggling subjects when it comes to PCB designing. In this blog, we have tried to explain all the things related to power integrity. We will be covering the following topics:

What is power integrity?
Power Distribution Network (PDN) block diagram
What is PDN noise?
Analysis and design of PDN
Power Integrity, Signal Integrity, and EMI are related

1. What is power integrity?

A circuit board requires one or more power supply voltages to operate. These are mostly generated by Voltage Regulator Modules (VRMs). These VRMs are designed to deliver the required maximum currents at the required voltages to the various devices on the circuit board.
Power Distribution Network (PDN) consists of all the interconnects from the VRMs to the terminals/pads of various components and devices (ICs, etc.) including all the bulk and ceramic decoupling capacitors, power and ground planes, the intervening vias, traces and the relevant leads, solder balls, wire-bonds, etc. of the device packages.
A PDN’s any voltage rail is a single net but a very large one, having many components connected to it, and is spread over almost the entire PCB. PDN is susceptible to electrical noise generated by the components, and the various signal, power and ground nets on the PCB. Furthermore, faster and greater the number of the signal transitions (rise and fall times) switching over various I/Os and internal circuits of the devices on the board, greater will be the magnitude and frequency bandwidth of the electrical noise on the PDN.
PDN noise is injurious to the proper functioning of the board in several ways:

When the magnitude of the noise on PDN exceeds a certain threshold, it alters the voltages delivered to the ICs below the acceptable values, causing malfunction of the circuits on the board.
Even if a PDN supplies  a voltage to the devices within tolerance, the PDN noise may still cause other problems. It can cause or appear as crosstalk on signal lines, it can transfer to the input power source line from where it can pass on to other VRMs inputs, thereby to their outputs.
Furthermore, as PDN interconnects are usually the largest conducting surfaces on the PCB and carry the highest currents, any high frequency PDN noise has the potential of creating a lot of  electromagnetic radiation, possibly causing failure to pass EMC compliance.

It is therefore important to control the PDN noise, and ensure that it delivers the required voltages within acceptable tolerance limits (usually within ± 2 to 5%), across the power supply voltage and ground terminals of the various devices mounted on the PCB, and the devices’ dynamic current demands are met at all times and over their entire functional frequency range.
Power Integrity (PI) deals with all aspects of the PDN – it is designed to control...

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