How to Adjust PCB Power Distribution Network Design?

The Power Distribution Network on a PCB encompasses the voltage regulator module and the IC pins and that is why people are quick to associate Power Distribution Networks or PDN with the power circuits that are employed to drive computer’s CPUs and FPGAs (i.e Field-programmable gate array which is used to implement custom hardware functionality without using soldering iron or breadboard). Due to the rise in usage of FPGAs in modern products, engineers are required to broaden their horizon regarding PDN design.

Figure 1.Printed Circuit Board Layout

Following are some tips for achieving close to perfect PCB Power Distribution Networks design:

1. The fundamental designing rule for Power Distribution Networks has taught engineers over the years that the only way of obtaining best performance is through a monotonous impedance profile (independent of frequency).
2. Power Distribution Network Design forms a critical part of a high-speed digital design which is used to provide less noisy power supply to the ICs within a particular peak voltage ripple to ensure smooth functioning.
3. Unbecoming results of a poorly designed PDN could either mean faulty circuits that no longer function due to a failure in maintaining adequate voltage regulation, or crosstalk circuits where the PDN noise flows through many different distribution paths such as PCB Crosstalk.
4. The act of switching transistors in the ICs results in a high-frequency current draw and produces simultaneous switching noises .This spreads  along the power distribution network from the chip towards the printed circuit board which causes various electromagnetic interference(EMI) and Signal Integrity (SI) difficulties.
5. High layer count Printed Circuit Boards (PCBs) have many power, power-return and signal-return planes and/or area fills in them which forms resonant cavities. In such PCB, the impedance of the PDN is conventionally used as a step towards analysing the power distribution network design because it can enables  to calculate noise voltage generated due to noise current.
6. That’s one of the reasons which makes the stability of power supply very important because a variable power supply could result in high impedance and consequently degrade the frequency independent or flat impedance profile and lower the entire circuit’s performance.
7. Since an impedance is not entirely independent of frequency, we can always adjust the designs to get the desired results. It is mandatory to have a suitable Power Distribution Network design to maintain voltage variations within noise boundaries so that a device could function without glitches.

Figure 2. Power Distribution Network Designed for High Impedance

Conclusion:

PDN design consists of resistance, inductance as well as capacitance associated with the PCB traces and planes. We know that the noise signals are created due to the impedance peaks in the power distribution network. Our most basic goal should always be to maintain the impedance as flat as possible to a bandwidth which varies with the edge speed of load signals, the amplitude of current change and the PDN’s impedance. There are several other methods, analysis and theories concerning PCB power distributed networks apart from the ones we’ve discussed in this article. After reading this piece, an engineer or engineering enthusiast might gain insight and knowledge regarding PDN issues and their effects on a circuit’s performance.