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AN-649

APPLICATION NOTE

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Using the Analog Devices Active Filter Design Tool

By Hank Zumbahlen

Table I. Chebyshev Cutoff Frequency to –3 dB Frequency

INTRODUCTION

The Analog Devices Active Filter Design Tool assists the

engineer in designing all-pole active lters.

their attenuation, group delay, step response, and impulse

response are presented. The lter tool is then employed

to design the lter. An example is provided.

STANDARD RESPONSES

Many transfer functions may be used to satisfy the atten-

uation and/or phase requirements of a particular lter. The

one that is selected will depend on the particular system.

The importance of frequency domain response versus

time domain response must be determined. Also, both

of these might be traded off against lter complexity, and

achieves its atness at the expense of a relatively wide

transition region from pass band to stop band, with aver-

age transient characteristics.

The values of the elements of the Butterworth lter are

more practical and less critical than many other lter

types. The frequency response, group delay, impulse

response, and step response are shown in Figure 1. The

pole locations and corresponding 

o

and  terms are

tabulated in Table II.

CHEBYSHEV FILTER

The Chebyshev (or Chevyshev, Tschebychev, Tsche -

byscheff, or Tchevysheff, depending on the translation

Chebyshev lters have 0 dB relative attenuation at dc.

Odd-order lters have an attenuation band that extends

from 0 dB to the ripple value. Even-order lters have

a gain equal to the pass-band ripple. The number of

cycles of ripple in the pass band is equal to the order of

the lter.

edge of the ripple band is at 

The 3 dB bandwidth is given by

o