Issue link: https://iconnect007.uberflip.com/i/1359517
14 DESIGN007 MAGAZINE I APRIL 2021 in particular, if you get the default IBIS model from the vendor's website, it has a default pin assignment, but once the EE places and routes the actual FPGA chip, you need to redefine the pin assignments for each signal. Now, the pin assignment of the FPGA that someone designs isn't the same as the one on the IBIS model, and that's where it all goes haywire. You think, "at simulation is simple. You just have to import the IBIS models into the transmission line model and click Go." at should happen, but, it doesn't. Where you don't have pin assignments match- ing, you have to manually select the required FPGA sub-models from the thousands of pins with 50 or so sub-models. And these have all got cryptic names that are different for each IC vendor. So, you actually have to find the model or driver model that matches the trans- mission line that you're trying to simulate. Or maybe you cannot find the model at all. Good luck sourcing a connector model. So, again, this all takes time. It took me years to figure out how to do it properly, quickly, and effi- ciently. e other thing is the cost of ownership, of course. e high-end simulation tools are expensive, as you know, and are beyond the budget of the average punter. So, it's better to outsource simulation. From a cost point of view, it's not all that expensive. Alternatively, EDA vendors have professional packages that include basic simulation tools. OrCAD has Signal Explorer, that I am now using; PADS has BoardSim EXT, a cut-down version of HyperLynx; and Zuken has tools like Light- ning in their CR-5000. ese are all entry level simulation tools, but they still require a lot of background knowledge to get them up and running. ey are not that simple to use. Shaughnessy: Do you basically have to be an SI or PI engineer to use simulation tools? Are there any simpler tools that fall under the simulation umbrella that, say, a PCB designer could use? Olney: Simulation tools encompass many sub- tools. For instance, stackup planning and PDN planning is all part of simulation and that can certainly be done by the average PCB designer. e stackup needs to be assigned before you even start placing a chip on the board. You need to define the differential pairs and accom- modate different technologies on the same lay- ers of the PCB. You may have a 50-ohm digital signal with 100-ohm differential pair. You may have a DDR3, which has 40-ohm single ended and 80-ohm differential impedance. You may have a USB that's 90 ohms. All these have to work on one substrate, so you need to account for all these different technologies and work out the impedance for all those before you even start your design. PCB designers can certainly do that. It's not difficult. It's pretty straightforward. PDN planning can also be done by the PCB designer. e optimization of the PDN is a trial-and-error process that needs to be done in conjunction with the stackup materials, planar capacitance, and decoupling, to fully Barry Olney