op-amp_active filters - Chapter 16 Active Filter Design...

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Chapter 16 Active Filter Design Techniques Literature Number SLOA088 Excerpted from Op Amps for Everyone Literature Number: SLOD006A
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16-1 Active Filter Design Techniques Thomas Kugelstadt 16.1 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 sig- nal conditioning stages. System power supplies often use band-rejection filters to sup- press the 60-Hz line frequency and high frequency transients. In addition, there are filters that do not filter any frequencies of a complex input signal, but just add a linear phase shift to each frequency component, thus contributing to a constant time delay. These are called all-pass filters. At high frequencies (> 1 MHz), all of these filters usually consist of passive components such as inductors (L), resistors (R), and capacitors (C). They are then called LRC filters. In the lower frequency range (1 Hz to 1 MHz), however, the inductor value becomes very large and the inductor itself gets quite bulky, making economical production difficult. In these cases, active filters become important. Active filters are circuits that use an op- erational amplifier (op amp) as the active device in combination with some resistors and capacitors to provide an LRC-like filter performance at low frequencies (Figure 16–1). LR C V IN V OUT V IN V OUT R 1 C 1 C 2 R 2 Figure 16–1. Second-Order Passive Low-Pass and Second-Order Active Low-Pass Chapter 16
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Fundamentals of Low-Pass Filters 16-2 This chapter covers active filters. It introduces the three main filter optimizations (Butter- worth, Tschebyscheff, and Bessel), followed by five sections describing the most common active filter applications: low-pass, high-pass, band-pass, band-rejection, and all-pass fil- ters. Rather than resembling just another filter book, the individual filter sections are writ- ten in a cookbook style, thus avoiding tedious mathematical derivations. Each section starts with the general transfer function of a filter, followed by the design equations to cal- culate the individual circuit components. The chapter closes with a section on practical design hints for single-supply filter designs. 16.2 Fundamentals of Low-Pass Filters The most simple low-pass filter is the passive RC low-pass network shown in Figure 16–2.
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This note was uploaded on 08/22/2011 for the course EEE 230 taught by Professor Subramanian during the Spring '07 term at University of California, Berkeley.

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op-amp_active filters - Chapter 16 Active Filter Design...

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