Issue link: https://iconnect007.uberflip.com/i/1174596
OCTOBER 2019 I DESIGN007 MAGAZINE 33 Shaughnessy: That is one thing we're starting to see more and more: the awareness that ev- ery trace is a transmission line. Ritchey: Because in the general world, things were still slow enough you could just hook stuff together. But if you were to go back to Amdahl in 1974, everything we had we creat- ed as a transmission line; people making high- speed stuff from day one had done that, but computer science people have not. And for the last 40 years, the goal has been to turn out good computers because that's where it ends, which is not electrical engineering. You can get a degree in computer science without a fields and waves course, which is all about transmis- sion lines. What happened was we rewarded that, and almost everybody who is in senior management now is a computer science major, but they don't understand all of this stuff, and they don't support their engineers who say, "What are we going to do?" Shaughnessy: Dan Beeker says that he did a lot of things right totally by accident when speeds were slower. Ritchey: The classic thing that people did was to "sprinkle capacitors around on the board." The two values they used were 0.1 µF and 0.01 µF, which don't work at the speeds we're doing things now. When things were slow, it didn't matter. And that's where the power delivery problem has come from: habits we started when things were slow. They didn't make any difference. When I was at the de - sign company, we had two clients who were each making a 3D graphics workstation, and at that time, it took a backplane and six big boards. There were 12 engineers, and each one had a different philosophy of using ca - pacitors, where to place them, how many, and how to hook them up. And there was one who, if you challenged what he was telling you, would get red in the face and want to fight you. You'd watch and say, "These people can't all be right." One of the products was surface mount, and the other was through-hole. One day, I received a call from the engineer on the through-hole project who was screaming in the phone. He was angry because he wanted to look at a sig - nal on the board, so he hooked the ground lead on his probe to what he thought was the ground end of a capacitor, and it burned out. He got a new ground lead and hooked it to the other end of the capacitor, and it burned up. It turned out that somebody had done something to the CAD system code and hooked up both ends of all the capacitors to +5 volts. All 12 of those boards had both ends of all of the capacitors hooked to +5 volts, and none went between +5 and ground, yet the boards still worked. And what's staggering me is that they re- quired all of the artwork to be redone, so all of the capacitors were hooked to +5 and ground, even though the evidence said they did noth- ing. I use this in a class as an introduction into why people got away with that for so long, and that's because the boards were larger and you accidentally had a good plane capacitor, which was doing the work. Things were slow enough that your bad habits were not hurting you. Shaughnessy: Now they hurt you. Ritchey: Yes, they do. I spent almost a year and a half-million dollars helping a client in Virgin- ia redesign a robot mop that mops Amazon's warehouses. It worked fine, but it wouldn't pass EMI, and it took me more than a year to clean it up. There's a whole industry of moth - erboards, computers, etc. You can buy them, hook them all together, and make something, which is what these people did, but none of those modules passed EMI. We had to help each supplier redesign their product so that it worked and passed EMI. The strange thing is that when you ship products into the consumer market, you have to certify that they've passed the main EMI standards, which always shocked me. But these people never bothered to do that, and they were shipping all kinds of product. If you get caught, you'll get fined $10,000 per unit you ship that's out of compliance. Shaughnessy: That's serious business, and it adds up.