Page 167 - DSP Integrated Circuits

152 Chapter 4 Digital Filters

Figure 4.40 Normal and complementary magnitude responses of a third-order wave
digital filter of Cauer type

EXAMPLE 4.9
Determine the stopband attenuation for the complementary output in the wave
digital lowpass filter just shown. The ripple in the passband of the normal output
is A max = 0.969 dB. Determine also the reflection coefficient.
We have

Let §i and $2 denote the maximum deviation in the passband of the normal
output and complementary output, respectively, as illustrated in Figure 4.40. The
largest deviation in the passband is

2
2
From Feldtkeller's equation we have (1 - 5i) + (% = 1
Thus, we get

and