Issue link: https://iconnect007.uberflip.com/i/1256432
18 DESIGN007 MAGAZINE I JUNE 2020 Shaughnessy: Has anyone ever talked to these IC companies and said, "Why don't you get your act in gear and have some designers do some input on these things?" They must know that people are out here saying that their app notes are bullshit. Why do they keep putting out bad info? Beeker: They're looking at circuits, and these aren't circuits. This is about high-speed ana- log. Their IP people have rules that were based on things that seemed to work 20 years ago and are now cast in concrete. It doesn't help that the simulation tools will back them up be- cause a simulator will tell you exactly what you want to see. It only looks at the three main elements: RLC. Hartley: The bottom line to all of this, and we've said it a couple of times without say- ing it, is there are two schools of thought about how circuits work: there's circuit theory and field theory. When I was in school, I was taught circuit theory, but so was Dan and every EE. I was also taught field theory, and I went to one of my other profs and said, "I'm hav- ing trouble with field theory." He said, "Don't worry about it. Do well enough to get through the class. What you need to understand is the circuit theory." He couldn't have given me worse advice because the truth is circuit theory is how things work on paper. Field theory is how things work in the real world. It's the physics behind how things function, and almost all engineers learn circuit theory. They learn voltage and current, but they don't learn enough about field theory. Matties: There are a lot of people working at these app notes along the way. Is there any community feedback to improve an app note beyond the OEM or the provider within the de- sign community? Beeker: There's a little bit, but not very much because most of the people, like Rick and me, were disgusted and ignored it. Or, like Rick says, "Use it to start your campfire." They don't understand it well enough to push back. Nolan Johnson: What do you see as the role of companies that are out there right now selling parts and library services and trying to imple- ment models based off of app notes? Beeker: Most of the time, that's pushed off on somebody else's desk. They don't take a role. What I keep telling my customers is that, if they can't go to a conference, hire one of these people to come and teach their team. The cost of one board's re-spin will more than pay for that class, and then you probably will reduce your cycles from three or four or five down to one or two max. If that isn't a good return on your investment, then you aren't paying atten- tion. Happy Holden: Where do new engineers go to get the real numbers on the laminates they may be working with or specifying? The 10 megahertz number from the IPC slash sheet is not going to be sufficient for the margins, nor do they mention temperature and humidity ef- fects on laminates. Hartley: Exactly. You and I both know to go to a datasheet for material and look at dielectric constant; they'll give you a number. What they need to give you is a graph that shows how it changes across temperature, humidity, and frequency, and they need to show you all the characteristics, such as the conductivity of the material. Beeker: A nanosecond edge is a gigahertz, so they're way out of line. Remember, 60 picosec- onds is a common signal now, and DDR is 12.6 gigahertz. Holden: My only experience with app notes was early on in the HDI rollout. I received calls from people designing reference boards for app notes for the IC companies, and they were asking me about HDI design rules, etc. I asked them why they were using HDI and what ma- terial, and they said they designed this board on a specific material and were going to use blind vias because they're low inductance. I said, "What kind of chip is this?" They gave it