What is FILTERS

Chapter 8 FILTERS

Lessons In Electric Circuits Volume II – AC Book
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Lessons In Electric Circuits Volume II – AC Book

  • Chapter 8FILTERSContents 196,8.1 196,What 196,is 196,a 196,filter? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 187 197,8.2 197,Low-pass 197,filters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 188 203,8.3 203,High-pass 203,filters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 194 207,8.4 207,Band-pass 207,filters. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 198 209,8.5 209,Band-stop 209,filters. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 200 211,8.6 211,Resonant 211,filters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 202 223,8.7 223,Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 214 223,8.8 223,Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2148.1What is a filter?It is sometimes desirable to have circuits capable of selectively filtering one frequency or range offrequencies out of a mix of different frequencies in a circuit. A circuit designed to perform thisfrequency selection is called a filter circuit, or simply a filter. A common need for filter circuits isin high-performance stereo systems, where certain ranges of audio frequencies need to be amplifiedor suppressed for best sound quality and power efficiency. You may be familiar with equalizers,which allow the amplitudes of several frequency ranges to be adjusted to suit the listener’s taste andacoustic properties of the listening area. You may also be familiar with crossover networks, whichblock certain ranges of frequencies from reaching speakers. A tweeter (high-frequency speaker)is inefficient at reproducing low-frequency signals such as drum beats, so a crossover circuit isconnected between the tweeter and the stereo’s output terminals to block low-frequency signals,only passing high-frequency signals to the speaker’s connection terminals. This gives better audiosystem efficiency and thus better performance. Both equalizers and crossover networks are examplesof filters, designed to accomplish filtering of certain frequencies.Another practical application of filter circuits is in the “conditioning” of non-sinusoidal voltagewaveforms in power circuits. Some electronic devices are sensitive to the presence of harmonics inthe power supply voltage, and so require power conditioning for proper operation. If a distorted187