# An Appendix to Filter Wizard 14 (Match Point)

If you have been following the “Filter Wizard” series, here are some answers to a few of the previous “homework assignments”. In this installment, guest columnist Jorge Garcia begins by saying:

I'm sure you are all familiar with the classical approach to filter design. First you get your specifications, and then you go through a few simple calculations to determine the required order and response type for the filter (Butterworth, Chebyshev, Cauer, etc.). From there you choose a suitable prototype circuit (Sallen-Key, LC ladder, etc) with a 1 radian/second center frequency. Then you open a volume of charts and select the normalized component values. With the end in sight you scale the prototype circuit to the desired center frequency. It's very methodical and very tedious to design this way (though if you can afford fancy software, that can make things easier).

This was the only method I knew to design filters, so imagine my surprise when I read Kendall's article “An Excellent Fit, Sir” where he describes designing a filter using a spreadsheet. My first reaction was amazement. No sophisticated charts, no pole zero relationships, determination of a response type, none of those overly complex equations I learned in school.

His method seemed far more intuitive and practical. The ability to analyze circuits on a spreadsheet, to use Excel Solver to optimize circuit values, this was a technique that in my mind was essential for not only filter design, but as a powerful tool in my toolbox. So if you've been following along with his articles, besides answering many questions about filter design, I'm sure a few questions have popped up that need some small clarification and that's what I intend to do.”

You can read the article, which first appeared at EE Times-Europe (Analog) , by clicking here .