Chapter 20. Active Filter Design Techniques
Thomas Kugelstadt
20.1. Introduction
What is a filter?
A filter is a device that passes electric signals at certain frequencies or frequency ranges while preventing the passage of others.—Webster.
Filter circuits are used in a wide variety of applications. In the field of telecommunication, bandpass filters are used in the audio frequency range (0 kHz to 20 kHz) for modems and speech processing. High frequency bandpass filters (several hundred megahertz) are used for channel selection in telephone central offices. Data acquisition systems usually require antialiasing low pass filters as well as low pass noise filters in their preceding signal conditioning stages. System power supplies often use band rejection ...

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