The Ultimate Sensor Nov 1, 2006 By: Ed Ramsden

In the original Star Trek series, DeForest Kelley played ship's surgeon Dr. Leonard McCoy. This character was especially memorable for his frequent medical pronouncement, "He's dead, Jim," and for his handheld medical scanner, a device that looked like a pepper shaker with a spinning cap. This magical sensor could instantly and noninvasively diagnose any medical condition.

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."