The Practical Side of Using EM Solvers


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Electromagnetic (EM) solvers based on Maxwell’s equations have proven invaluable in the advancement of digital electronics and wireline communications. Plain and simple, electrical engineers need to know what a circuit or electrical interconnect will do when excited by a dynamic or varying signal. In the signal integrity world, an interconnect that passes a DC connectivity check can completely fail at higher frequencies. In the power integrity world, a power rail that measures the correct DC voltage could easily go into oscillation when a dynamic load is applied. Learning the basic skills to fire up an EM simulator, obtain qualitative answers in minutes, and higher fidelity answers in a few days, can be the difference between sleepless nights of product failures vs. robust designs with wide design margins.

In the beginning and even today, EM simulators are constantly in search of the right balance between accuracy and speed to “mesh” a three-dimensional structure and acquire the right answer. In the search for the ultimate solution to Maxwell’s equations, whether it is in the frequency domain for finite element methods (FEM) or in the time domain for finite difference time domain (FDTD), the user interface often suffers. Setting up ports, boundary conditions, and mesh topology might give the guru user additional flexibility. For most of us, we need automation to reduce the repetitive tasks.

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Figure 1: 3D EM simulators like PathWave ADS SIPro and PIPro make it easy to select nets and auto assign ports for fast EM setup and simulation. EM current density results on the right for a DDR4 DIMM board show how the power delivery at 10 kHz comes from the J1 edge connector, but at the higher 10 MHz frequency the power is being delivered by the on-board capacitors.

The good news is the processing speed of modern computers and low-cost memory has made it much easier to maintain significant accuracy while increasing speeds. This has enabled increased investment in optimizing user interfaces for specific applications, like simulating multi-layer laminate PCB designs. The improved user interfaces like Keysight’s PathWave ADS SIPro and PIPro rely on robust importing of EDA PCB CAD data, which include stackup, nets, and components for easy selection of nets and components for simulation. Ports can be automatically assigned, and default meshing and boundary conditions enable users to be up and running with an EM simulation in a matter of minutes.

However, simulators are notorious for “garbage in equals garbage out.” Here are a few tricks of the trade to ensure a proper setup.

To read this entire article, which appeared in the July 2022 issue of Design007 Magazine, click here.

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