# SPICE Made Easy

Check out this handbook for the LTspice IV Simulator from Wurth Electronik, as reviewed by EMC expert Ken Wyatt.

*Check out this handbook for the LTspice IV Simulator from Würth Elektronik, as reviewed by EMC expert Ken Wyatt.*

One of the most popular versions of SPICE today is Linear Technology's LTspice IV. This free and full-featured SPICE modeling software runs on PCs and includes schematic entry, great graphical plotting, and is very fast. While Linear Technology provides a basic online user guide, until now, there really hasn't been a very comprehensive resource on using the software. Earlier this year, components supplier Würth Electronik alleviated this missing reference with its 700+ page book, *The LTspice IV Simulator - Manual, Methods and Applications* by Gilles Brocard.

This monster four-pound book was introduced this last May and costs €49, or US$49.99, orderable through the WE Midcom website or your local sales rep. This comprehensive user manual is divided into 21 chapters, covering everything from the history and basics of SPICE, to the schematic editor, to making measurements with the voltage and current probes, to analyzing circuits. There are several examples throughout the book.

*LTspice IV* has no limits on the number of nodes, components, models, or measurements. The schematic editor makes entering your circuit easy -- no more assigning node numbers and entering the circuit as a list of components. It's easy to add voltage and current probes throughout your circuit. Best of all, it's a free download from Linear Technology.

The book starts out with an interesting history of SPICE and its development. Chapter 3 starts out with a simple op-amp driving a couple transistors. This example steps you through many of the basic features of the software, including defining various sources and plotting the results. One feature of interest to EMC engineers (and other designers concerned with distortion and resulting harmonics) is the FFT analysis theta may be performed.

Chapters 4 through 6 cover all the aspects of using the schematic editor. It demonstrates how to use the component library and how to modify the various component parameters. Because Würth Electronik specializes in ferrite components and transformers, there is an extensive library of these components, plus the very large library of Linear Technology's semiconductor devices. SPICE models from other manufacturers are readily available and downloadable from several sources. Chapter Eight describes how to define the six different measurement types LTspice can perform, as well as how to use the virtual oscilloscope and the FFT editor. The oscilloscope has both conventional time versus voltage and x-y scales.

Chapters 9 and 10 cover all the six simulations in more detail: DC simulations (operating point, transfer, and sweep), AC simulation (AC analysis and noise) and Non-linear (transient). Chapters 11 and 12 cover numeric measurements, downloads, backup, and importing of circuit models (sub-circuits). Chapter 13 has extensive coverage on how to edit your voltage and current sources in order to produce more customized simulations. There are many examples. Chapter 14 explains passive components and how to modify their parameters to fit your specific circuit and simulation needs. LTspice also includes the ability to program in the hysteresis for ferrite components. The chapter also includes information on transformers.

Chapter 15 explains how to use all kinds of semiconductor devices. Chapter 16 includes information on what the author terms "accessory components," that is, voltage and current-controlled switches, lossy and lossless transmission lines, special functions, and sub circuits. Chapter 17 extensively covers inductors, transformers, the hysteresis cycle, and mutual inductance. Chapter 18 is a review of the control panel and keyboard shortcuts, which I think should perhaps have been moved up closer to the front of the book. It does tend to tie all the features together, though.

Chapter 19 is where you'll find a myriad of examples, from characterizing JFETS, transistors, and zeners, to characterizing amplifiers, to working with the FFT feature. It also demonstrates how to analyze the gain-phase bode plots of an amplifier. DC-DC converters are covered extensively, because that's a specialty of Linear Technology. Chapter 20 includes a host of questions and answers on various topics, and includes hints and tips on using LTspice successfully. Chapter 21 includes modeling information on inductors and transformers and includes several hints on how to model and use these components in your simulations.

All in all, I found the book to be useful for both the novice and more advanced users. I use LTspice quite a bit in my consulting practice, and I've found this handbook to be a valuable addition. If you don't already have the latest copy, it may be downloaded for free from Linear Technology's website. You can order the book and review an extract here. Highly recommended.

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