Introduction
Are you just getting into software simulation and feeling a little overwhelmed with all the new jargon? If this is the case, please read on. This brief article will explain some of the most common terms used in the very exciting world of EMC/Signal Integrity simulation software, all in one location.
Electromagnetic Simulation (aka EM Simulation)
A numerical analysis technique that solves electromagnetic field distribution problems, described by Maxwell equations.
Common Numerical Analyses Techniques
- Finite Difference Time Domain (FDTD)
- Finite Element Method (FEM)
- Method of Moment (MoM)
FDTD
Finite Difference Time Domain (FDTD) can handle arbitrary 3-D structures and includes full-wave EM simulations. FDTD can handle larger and more complex problems in the time domain. Examples include EM simulation of full-size cell phone antennas and EM simulations per each port. FDTD is best used for time-domain reflectometry (TDR), EMI analysis and signal integrity and transitions. FDTD is most efficient for high number of mesh cells and uses a sequence of direct calculations instead of matrix type of solver. FDTD is a highly parallelized approach and can take advantage of GPU acceleration for antenna placement on automobiles and planes and biological analysis with complex human body models such as specific absorption rate (SAR).
FEM
Along with FDTD, Finite Element Method (FEM) can handle arbitrary 3-D geometries such as connectors, integrated circuit (IC) bond-wires, packages, waveguide and 3-D antenna structures. FEM is most efficient for use with multi-port applications. FEM solves for all ports in a single simulation including packages and interconnect networks.
MoM
Method of Moment (MoM) is most efficient for planar, multilayer applications such as IC passives and interconnects, RF PCB interconnects, high-speed PCB signal integrity analysis, and planar antennas.
Both FEM and MoM solves natively in the frequency domain and are best suited to performing analysis for high Q applications such as RF/MW filters and oscillators.
Field Simulators
Field simulators are utilized in modeling electromagnetic interactions among transmission lines in multiconductor structures and to estimate trace impedances (Z), propagation velocity (v), and all self and mutual parasitics (inductance and capacitance). The outputs are matrices that characterize the effective inductance and capacitance values of conductors. These matrices are important because they form the basis of all equivalent circuit models and are useful in obtaining accurate values of characteristic impedance (Z0), propagation velocity (v) and crosstalk. Field simulators are categorized as either electrostatic or two-dimensional (2-D), or as full-wave, also known as three-dimensional (3-D).
Two-dimensional (2-D) Field Simulators
2-D or electrostatic field simulators are based on static computations of the electric field. They provide inductance and capacitance matrices as a function of conductor length so they are an appropriate method for interconnect analysis and modeling. 2-D field simulators are very easy to use and take a short amount of time to complete computations (within seconds). Their weaknesses are in their inability to handle complex geometries and also their inability to compute frequency-dependent effects such as internal inductance or skin effect resistance.
Three-dimensional (3-D) Field Simulators
3-D or full-wave field simulators solve Maxwell’s equations directly for any arbitrary geometry. As such, they don’t have the same limitations as the 2-D types. Unlike 2-D field simulators, 3-D field simulators are able to compute complex three-dimensional geometries and predict frequency-dependent losses, internal inductance, dispersion, and most other electromagnetic phenomena. Their weaknesses are that they are more difficult to learn and use and simulations can take hours or days, instead of seconds like the 2-D types. The output of a 3-D field simulator is sometimes of the S-parameter type, which some find not very useful for interconnect simulations for digital applications.
LTspice®
Originally created by Linear Technology, LTspice® is a high-performance SPICE (Simulation Program with Integrated Circuit Emphasis) simulation software, schematic capture and waveform viewer with enhancements and models for easing the simulation of analog circuits. Various versions of SPICE are available for download, sometimes free of charge.
Also found on web are technical articles, upcoming technical upcoming seminars, videos, and other helpful information for learning more about SPICE and how to use it. Unlike some of the other simulation techniques mentioned above, the learning curve for SPICE is probably the shallowest.
References and Further Reading
- Stephen H. Hall, Garrett W. Hall, James A. McCall, High-Speed Digital System Design – A Handbook of Interconnect Theory and Design Practices, John Wiley & Sons, 2000
- Signal Integrity Journal. (2017, August 7). 5 Leading EDA Tools for EMC/EMI Design Challenges.
- Interference Technology. (2017, November 28). Simulation in EMC.
- Tera Analysis, Ltd. EMC Analysis with QuickField.
- Keysight Technologies, Inc. EMProWorkshop, Version 4.0 Updated February 2015.
- Electronics 360. (2017, October 24). Why is EMC Simulation Taking Off?
- Altair Blog. EMC simulation during the product development process by Jordi Soler (2016, July 6).
- EM Simulation for EMC: Keeping a lid on interference (2010, July 15).
