Page 90 - DSP Integrated Circuits
P. 90
3.10 Frequency Response 75
Figure 3.12 Magnitude response for the third-order digital lowpass filter
The pole-zero configuration is shown in Figure 3.16. A Cauer filter has equirip-
ple in both the passband and the stopband. Notice the transmission zeros at coT ~
96° and crfT = 180°, i.e., in the stopband. We will discuss digital filters in more
detail in Chapter 4.
3.10.2 Attenuation Function
Instead of using the magnitude function, it is more common to use the attenuation
function, which is defined
The magnitude function on a logarithmic scale (dB) is the same as the attenu-
ation function, except for the sign. The maximum power that is transferred
between the source and load is obtained at the frequencies of the attenuation
zeros. There are two attenuation zeros in Figure 3.13: the first at coT = 0 and the
second at about 65°. The transmission zeros correspond to frequencies with infi-
nite attenuation and are therefore called attenuation poles.
