With the recent introduction of cheap ?? analog-to-digital converters (ADCs) offering resolutions of 24 bits or more, you'd think that the digital revolution is complete, and that the need for analog design has passed. Twenty-four bits gives you a resolution of better than 1 ?V on a 10 V span, so these high-resolution converters will make it easy to solve many interfacing problems with a minimum of additional circuitry.

Last month we discussed a number of simple passive filters in both low-pass and high-pass configurations. Although these filters could reject out-of-band signals, this capability was relatively limited because they all had an attenuation roll-off rate of –20 dB/decade. You will find that many applications require a much greater ability to reject out-of-band signals than that provided by the passive low-pass filters we looked at.

Back in the late 1970s comedian Don Novello (a.k.a. Father Guido Sarducci) had a routine called the "Five-Minute University," which was supposed to impart to you, in the span of only five minutes, all the knowledge you would retain five years after graduating from a regular university. So, in the same spirit, I offer "Dr. Ed's Five-Minute Analog Filter Design University."