1 Introduction
This document is intended for designers that do not have the time to check filter theory in old
college textbooks—and try to translate transfer equations into something that can be put into
production. This is like looking at the back of the textbook for the answer. Speaking of the back
of the book—Appendix B contains a brief introduction to the filter circuits given here, and the
limitations of this quickie approach to design.
To design a filter, four things must be known in advance:
• The power supplies available: positive / negative—or only positive (single supply)
• The frequencies that need to be passed, and those that need to be rejected.
• A transition frequency, the point at which the filter starts to work—or—a center frequency
around which the filter is symmetrical.
• An initial capacitor value—pick one somewhere from 100 pF for high frequencies to 0.1 μF
for low frequencies. If the resulting resistor values are too large or too small, pick another
capacitor value.
Ready? Let’s design the filter. Pick the filter type from one of the following 6 options that
represents the frequencies to be passed (shaded area):