Chapter 16 - Active Filter Design Techniques

Abstract

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 filters to suppress the 60-Hz line frequency and high frequency transients. Active filters are circuits that use an operational amplifier (op amp) as the active device in combination with some resistors and capacitors to provide an LRC-like filter performance at low frequencies. This chapter introduces the three main filter optimizations-Butterworth, Tschebyscheff, and Bessel. It also describes the most common active filter applications: low-pass, high-pass, band-pass, band-rejection, and all-pass filters. It concludes with a discussion of all pass filter design. An all-pass filter has a constant gain across the entire frequency range and a phase response that changes linearly with frequency; due to these properties, all-pass filters are used in phase compensation and signal delay circuits.