Page 147 - DSP Integrated Circuits

132 Chapter 4 Digital Filters

where the constants are given in Table 4.2 and

Filter type ci 02 03
Butterworth 1 1 &o 2
Chebyshev I and II 1 2 HI
Cauer 8 4 2k 4
Table 4.2

Equation (4.23) can also be used to determine the required order for the corre-
sponding digital IIR filter. We demonstrate the computational details with an
example.

EXAMPLE 4.3

Determine the required order for a digital Cauer filter that shall meet the follow-
ing specification:

We get from Equations (4.22) and (4.23)

Finally, we get

The frequency transformations just discussed yield suboptimal solutions for
bandpass and stopband filters that shall meet more general requirements—for