Page 198 - Analog and Digital Filter Design

Bandpass Filters 1 9

QI Q2 I"

Figure 6.14 P
Cauer Pole and Zero Pairing

To design a Cauer, or Inverse Chebyshev, filter a different circuit topology is
required. The Cauer response has zeroes outside the passband, so a notch-
generating circuit is required. Notches can be produced using a circuit that is
an extension of the state variable filter, and is known as a biquad. This circuit
is illustrated in Figure 6.15.

R3

C

..
..
=.
i'C
R I

Figure 6.15
The Bandpass
Biquad Filter