Chapter 22
Active Filters
22.1 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, band-pass filters are used in the audio frequency range (0 kHz to 20 kHz) for modems and speech processing. High-frequency band-pass filters (several hundred MHz) are used for channel selection in telephone central offices. Data acquisition systems usually require anti-aliasing 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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