Digital Filters - Signal Processing of Random Physiological Signals - page 111

CHAPTER 11

Digital Filters

This chapter will review the concept of filters before presenting an overview of digital
filters. It is not the intent of the chapter to enable the reader to write digital filter pro-
grams, but rather to present the engineer with the ability to use application software
with filters and to choose the proper filter for specific biomedical applications. Let us
start with the basic question, “What are Filters?” By definition, “Filters are circuits
that pass the signals of certain frequencies and attenuate those of other frequen-
cies.”

11.1 CLASSIFICATION OF FILTERS
The most common classification or types of filters are as follows:

1. Low-pass : pass low frequencies; block high frequencies

2. High-pass : pass high frequencies; block low frequencies

3. Band-pass : pass a band of frequencies

4. Band-reject : attenuate a band of frequencies

5. All-pass filter : used for phase shifting

In addition filters are also categorized as follows:

1. Butterworth

a. Low-pass filter

b. High-pass filter, etc.