Fear, uncertainty and doubt (FUD) relating to power distribution networks (PDN) is rampant in the industry today. Where once there were only one or two main power supplies to deal with on PCBs, today there are often 10 or more on large complex designs, with each one having their own voltage regulator modules (VRM) and power puddles or planes. Coupled with the fact that large ASIC s or FPGAs operate with core voltages at less than 1 V, and instantaneous current draw on the order of 30 amps or more, trying to maintain a low transfer impedance in milliohms over the frequency range of concern is a challenge.
That’s why when I learned that Eric Bogatin was teaming up with Larry Smith to write a book titled, Principles of Power Integrity for PDN Design—Simplified,I knew I had to get it once it was published. Well the wait is over, and I received my copy just before Easter.
If you have read any of Eric’s previous books on signal integrity, you will feel right at home reading this one. His writing style, along with Larry’s deep grasp of the physics surrounding PDN design and IC technology, combine to simplify a complex subject into practical solutions without going into heavy mathematical equations, thereby eliminating most of the FUD.
The book is mammoth 786 pages with 10 chapters. It is organized in such a way as to act as a training manual for the power integrity practitioner. I do recommend starting at the beginning and reading right through because each chapter builds on the other.
The following is a very brief synopsis for each chapter:
Chapter 1 defines a PDN ecology as, “the entire series of interconnects from the pads on the die to the pads of the VRM,” and stresses why low impedance is so important over the frequencies of interest.
Chapter 2 builds on chapter 1 with more detail on impedance profile and how the properties of series and parallel RLC circuits play a part in it. They also reveal how a free version of a SPICE simulator can be used to analyze impedance.
Chapter 3 shows us special techniques on how to properly measure low impedances of components and the entire PDN ecology of less than 1 milliohm.
Chapter 4 is devoted entirely to inductance. It goes into great detail on explaining what it is, how it is affected by physical design, and how to estimate loop inductance from physical features of the PCB.
Chapter 5 gives a thorough study on multi-layer chip capacitors: from how they behave individually to how they behave together to manage the peaks in the impedance profile.
Chapter 6 delves into the properties of power and ground planes and how the capacitors interact with them. Spreading inductance, which is the most important property of planes, is explained in great detail.
Chapter 7 takes a bit of a detour to explore another function of a PDN with respect to signal integrity and how important it is to provide a low impedance path for signal return currents.
Have you ever heard of the term, “Bandini Mountain” and how it relates to the PDN Ecology? In chapter 8 you will learn the origin of the term, what causes it, why it is so important and steps you can take to mitigate its effect.
Chapter 9 talks about transient currents drawn by CMOS circuitry and how they interact with the PDN impedance profile. We also learn how several parallel resonant peaks of similar height above the target impedance and high q-factor can lead to the rogue wave effect.
Chapter 10 ties everything together and gives a practical approach to PDN design. A simple spreadsheet-based analysis technique is used to explore design space and followed up by simulations. Several design examples are worked through in great detail to reinforce principles introduced in this book, and verify the spreadsheet. You can download it from Eric’s web site (located here).
Overall I found this to be an excellent reference book, and I can see it being my main “go-to” book for power integrity. I especially liked the fact that the equations are not intimidating and almost every time each term is explained right after, regardless if the equation is repeated from somewhere else in the book. This makes it convenient when referring back to different sections without having to search through earlier chapters to find out what certain terms meant.
In short, if you are looking for a good book to help you understand PDN design, then this book is a good place to start. I know if it’s like any of Eric’s other books I own, I can see it becoming well highlighted and bookmarked going forward.