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CHAPTER 8<br />

IIR Filter<br />

Design<br />

IIR filters have infinite-duration impulse responses, hence they can be<br />

matched to analog filters, all of which generally have infinitely long impulse<br />

responses. Therefore the basic technique of IIR filter design transforms<br />

well-known analog filters into digital filters using complex-valued<br />

mappings. The advantage of this technique lies in the fact that both<br />

analog filter design (AFD) tables and the mappings are available extensively<br />

in the literature. This basic technique is called the A/D (analogto-digital)<br />

filter transformation. However, the AFD tables are available<br />

only for lowpass filters. We also want to design other frequency-selective<br />

filters (highpass, bandpass, bandstop, etc.). To do this, we need to apply<br />

frequency-band transformations to lowpass filters. These transformations<br />

are also complex-valued mappings, and they are also available in the literature.<br />

There are two approaches to this basic technique of IIR filter design:<br />

Approach 1:<br />

Design analog<br />

lowpass filter<br />

−→<br />

Apply freq. band<br />

transformation<br />

s → s<br />

−→<br />

Apply filter<br />

transformation<br />

s → z<br />

−→<br />

Desired IIR<br />

filter<br />

Approach 2:<br />

Design analog<br />

lowpass filter<br />

−→<br />

Apply filter<br />

transformation<br />

s → z<br />

−→<br />

Apply freq. band<br />

transformation<br />

z → z<br />

−→<br />

Desired IIR<br />

filter<br />

386<br />

Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s).<br />

Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.

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