Digital Signal Processing Reference
In-Depth Information
Chapter 4
Analog Filter Implementation Using
Active Filters
In this chapter, we will discuss the implementation of the analog approximation
functions that we developed and verified in previous chapters. There are several
methods that could be used to allow the successful implementation of an analog
filter. Unfortunately, an entire topic could be devoted to this topic (and several
have), so we will concentrate on active filters. Using active filters to implement
the transfer functions is a very popular method today because of the natural
correspondence between the analog circuit and the mathematical function. We will
not discuss the derivation of the transfer functions for active filters because the
development of such circuit analysis techniques is beyond the scope of this text.
However, a number of suitable references are given in the analog active filter texts
of Appendix A for those who are interested in the derivations. Instead, the circuit
topology and transfer function for several common active filters will be presented
before determining the component values for each circuit. We will develop
implementation procedures for each of the filter selectivities discussed in previous
chapters as well as discuss other options for implementation and some of the
important implementation issues.
4.1 IMPLEMENTATION PROCEDURES FOR ANALOG FILTERS
There are many choices when it comes to implementing our continuous-time
analog filters. For example, we could describe our single-input and single-output
system by means of state variables and use a state-space approach to the problem.
This method has the advantage of being very general and it puts the problem in a
convenient mathematical form that allows manipulation in terms of matrix
algebra. However, the development of this theory is beyond the scope of this text,
but several references in Appendix A provide insight to this method.
When considering the method of implementation, two key factors of
frequency range and the power handling capability of the filter also come into
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