Issue link: https://iconnect007.uberflip.com/i/1472851
JULY 2022 I DESIGN007 MAGAZINE 13 simulation from a layout database, chances are you've used a 2D solver whether you knew it or not. 3D solvers are used when you want to solve an arbitrary three-dimensional structure with high accuracy, usually vias, package breakouts, or high-speed connectors. 3D solvers discretize (mesh) the structure's entire volume and solve Maxwell's equations, which requires prodi- gious amounts of compute power and mem- ory. 3D solvers present the most demanding technical challenges and generate the most dis- cussion, so when someone says "field solver," that's usually what they're talking about. ere are multiple types of 3D solvers, but for our current purposes we can just say that 3D solv- ers are used when the structure to be modeled can vary arbitrarily in the X, Y, and Z dimen- sions. Finally, hybrid solvers are in-between 2D and 3D solvers. ey're best suited to large struc- tures that are essentially planar, like printed circuit boards. ey use a variety of different techniques to identify and solve the differ- ent regions and behaviors in a structure, then integrate those results to provide the inter- connect's overall behavior. ey're well suited Nolan Johnson: Bill, when you said margins are dropping, are you talking design margins, con- straint margins, or something else? Hargin: Actually, both. Let's take PCI Express as an example because it's widely known. e data unit interval (UI) and its associated sam- pling region gets smaller from one generation to the next, because the data rate typically doubles. at means the signaling margin you must work with goes down, which ultimately means that the physical constraints on the lay- out have to become tighter. Consider this analogy: You're driving through a course marked with traffic cones in a parking lot. If you're driving at 10 miles an hour, it's easy to stay on the path and avoid the cones. If you double your speed, it gets harder; if you double your speed again, it starts to get tough. at analogy assumes the cones stay in the same place; in the case of PCI Express, we'd not only be driving faster, but moving the cones closer together as well. Happy Holden: Are all field solvers created equal? Is it true that the faster they operate or the more accurate they are, the more expen- sive they are? Johnson: And how do you determine which field solver is the right one for you? Westerhoff: Great questions. It depends on what you're trying to model, and the level of accuracy that you need. ere are three dif- ferent fundamental kinds of field solvers: 2D, hybrid, and 3D. 2D solvers are used when you have intercon- nect that has a constant cross-section, usu- ally signal traces and cables. A 2D field solver provides the electrical characteristics per unit length, which are used as inputs for corre- sponding trace or cable elements in a circuit simulator. 2D solvers are well established, and they're built into many different simulation tools. If you've ever run any kind of post-layout Todd Westerhoff