How’s the impedance of your ground plane? Do you look at your power rails in the frequency domain? Mike Hoffman and Daniel Bogdanoff sit down with power integrity expert Kenny Johnson to discuss the latest trends and techniques for measuring power supplies in today’s electrical engineering podcast.
00:15 Kenny gave us a tip during scope month
01:26 There are two types of power people.
There are power producers, like the wind farms, power plants, and AC/DC adapter creators
There are power consumers, who care very much about their power quality. The ripple on power supplies, etc.
3:03 Power integrity is the study of the effectiveness of the conversion and delivery of DC power from the source to the gates on the IC.
3:45 If Moore’s Law holds out for another 600 years, we will have a computer that is capable of simulating every atom in the known universe.
4:35 Thermal hotspots were causing problems, so voltage levels started dropping
5:00 Kenny went to Amazon to look for a power integrity book. There were only 2-3 books a few years ago
Power integrity has been a thing since the 1930s
5:50 Product functional reliability is directly proportional to the power quality in a product.
We’re supplying a voltage to devices, but also current. So, this starts to look a lot like Ohm’s law.
A device has both power and a ground plane.
Power integrity pioneers include Istvan Novak and Ray Ridley and they talk about flat impedance power planes.
7:15 Flat impedance power planes – divide the supply power by the peak current, multiply it by your tolerance, you get a target impedance for your power planes.
If you can maintain a frequency flat impedance, you don’t see noise on your power supplies.
7:55 Think back to circuits 101, an inductor is open at a high frequency. And, a power plane is basically a big inductor. If you are, for example, writing high speed digital data to memory, it will be a problem.
8:40 When you look at boards, you see bypass capacitors to counteract the inductors
10:30 Experienced engineers use a lot of intuition when working out power distribution. Now, there’s a lot of localized power distribution.
11:15 A typical SSD has 12 power supplies
A tablet can have 50 power supplies
Some of our oscilloscopes have 180 power supply rails
Next generation mobile electronics 100-200 power supplies
12:25 There are redundant power supplies spread out across the device to help improve reliability. For example, there may be multiple converters that all power the same rail to help spread the loads.
The reason intuition is used is that a lot of people don’t have access to good simulation tools. They just have to use some rules of thumb and over-engineer the device to try to get reliability.
15:10 Kenny has a lot of patents. Our CTO Jay Alexander used to hold the record for most patents at the Colorado Springs site. Kenny has nearly 30 patents.
17:15 Kenny started as a probe designer, then got into power integrity.
Kenny recommends one by Bogatin about signal integrity, and a second edition called Signal Integrity and Power Integrity
18:35 SIPI labs – signal integrity and power integrity lab. Power integrity will affect your signal integrity, your EMI (electromagnetic interference) and your EMC (electromagnetic compatibility). (measure power integrity with a power rail probe)
So, the progressive companies have these SIPI labs. There are more advanced tools available.
20:10 Multiple papers say that power supply induced jitter is the single biggest source of data jitter in a digital system.
Kenny has some IOT development kits, and it’s easy to make them drop bits. Dropping bits will have an effect on battery life, performance, etc.
21:08 How to clean up a power supply? The majority of the time, it’s easiest to use a bypass capacitor. After you’ve looked at your supply in the time domain, look at it in the frequency domain. That will help you debug where the noise is coming from. And, if you know the frequency you are having trouble with, you can work backward into a bypass capacitor
22:42 There are some general rules that seem to apply to everything in electronics. Closer to the device is always better.
Next podcast – wide bandgap! The US Department of Energy will pay for some people to go back to university and get a degree in power engineering. Wide bandgap semiconductors have a huge potential to reduce energy usage.