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16 DESIGN007 MAGAZINE I APRIL 2021 ing and there's always one number on there that just doesn't fit, and you've got to work it all out. You can generally go back to the actual physical component and measure it. ere's always something wrong with the datasheet. Shaughnessy: I remember the big three EDA companies were talking about having simu- lation tools that would run concurrent with the design, like they would be running during schematic and all through. Is that how it is now or is it something that is right at the very end? Olney: Ideally you need to do that, yes. You need to simulate the schematic, which you can do. You can create freeform schematic models and then add an estimate of the lengths of the transmission lines. For example, for memory you may say, "I have two and a half inches here. So, I'll put a two-and-a-half-inch, 50Ω, trans- mission line, attach an IBIS model at either end and see how it goes." at's really good for building up the maximum length you have to play with because before you do the placement you need to know the maximum timing you can have on a chip. If you place the chips too close together it's difficult to route, and if they are too far apart then it may mess up your transmission lines with long delays and too many reflections. So ideally you need to work out the place- ment before you put the chip on the board, and that also helps with your routing topology. You may want to do flyby topology—that's how you generally do DDR3 and DDR4—but there's no need to do a flyby if you've only got a couple of memory chips. You can still do a T-topology route, which means branching out with equal delay into each chip. All the professional EDA tools now have a way of extracting the topol- ogy, so once you have routed a particular sec- tion you can extract the topology of that from the PCB, so you get the physical transmission line. at includes whether it's running on microstrip or asymmetric stripline, for exam- ple. It builds the actual physical structure of the PCB, including layer transitions (vias), into the simulation model. en you can virtually simulate the board itself, so that's the final pro- cess—making sure all the timing is right on the physical simulation. Holden: Does anybody publish or sell a good dielectric material library? Olney: I do (laughs). Actually, our stackup plan- ner has 35,330 individual materials at different frequencies. ere is a choice of over 700 series of rigid and flexible dielectric materials from over 60 manufacturers. ere is every material you would ever need. If you can't find a new material, I'll add it free of charge. It's very com- prehensive. Shaughnessy: What good sources of informa- tion on simulation analysis are out there? If someone is new to the industry, what would you recommend to them as far as getting some more information? Olney: Well, I think reading your magazine, Andy, is a good start, and other industry maga- zines. e SI Forum is a really good source of information with many experts on there that can answer your questions, as is attending any of the technical seminars that Rick Hartley and people like him run. ey are a good start. I Much of high-speed simulation is centered on achieving a nice eye diagram.