CHAPTER FIVE

Active Filters

5.1 FILTER FUNDAMENTALS

A filter, be it an oil filter, a lint filter, a furnace filter, or an active filter, accepts a wide spectrum of inputs, but only passes certain of these inputs through to the output. In some cases, it may pass through the “good stuff” while it catches the “bad stuff.” An oil filter in your car is one example. Other applications require a filter to catch the “good stuff” and let the “bad stuff” pass through. A gold prospector’s sieve is an example of this type of filter action. In both of the preceding examples, the filter discriminates between “good“ and “bad” on the basis of physical size (i.e., size of the dirt particle). In the filters discussed in this chapter, the “good” and “bad” signals ...

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