What I Learned this Month

Measurements are the anchor to reality. There is no substitute for building something and measuring it. However, a good simulator can often get you to an acceptable answer quickly by helping you answer “…it depends” questions and explore design space.

We often refer to the results of a simulator as a “virtual prototype”.

Of course, whenever you use a simulator, it’s important to practice “safe simulation”. I describe this as my rule #9, from my list of ten rules:

rule #9: Never do a simulation or measurement without first anticipating the result. If you are wrong, there is either something wrong with your intuition or with the set up of the tool or with the tool itself. Either way, by exploring the difference, you will learn something important. If you are correct, you get a nice warm feeling that you might actually understand something.

With this perspective, I think it is critical for every electrical engineer to have a simulator handy and use it to quickly answer “it depends” questions. A numerical simulator is just one of the three analysis tools every engineer should use. All three: rules of thumb, approximations and numerical simulation tools, are equally important and each have their own balance between accuracy and effort to get an answer.

Unfortunately, many questions involving impedance, reflections or transmission lines are too complicated to get even a reasonably accurate answer using rules of thumb or approximations and numerical simulation is essential.

I’ve explored many free versions of SPICE and have found QUCS to be the best tool for signal integrity problems. This is why I use it in all of my classes and feature it in some of our hands on labs.

At the 2012 IEEE EMC Symposium, I gave a presentation introducing QUCS and created five simple, yet valuable examples of QUCS circuits. These circuit files, as well as an executable version of QUCS, are available for free download from my web site.

If you want to accelerate up the signal integrity learning curve, I strongly suggest you take a look at QUCS. Of course, it doesn’t do everything you may want, like HyperLynx or ADS or Simbeor, might do, but it’s free!

QUCS should be one of the important tools in every engineer’s tool box to help you get to the correct answer, faster.