Active filterII - Resistance Simulation 2 1 2 1 V V Cf V V...

5.2 Active Filters (CONT…..)
Band-Reject Sections :
1 ) 2 ( 2
) 1 (
) (
2 2 2
2 2 2
1
2
+ - +
+
= =
s A RC s C R
s C R A
V
V
s H
V
V
In the above equation we observe that ϖ
o
= ϖ
r
= 1/RC and the Q
of the notch is determined by the gain A
V
= 1 + R
b
/R
a
of the Op-
Amp stage. Inspection of the equation also indicates that stability
requires A
V
<2.

(a) A low-pass-high-pass cascade to form a broad-band band-
pass circuit. (b) The frequency-response characteristics of the
low-pass and high-pass networks result in the (c) band-pass
response of the cascade.

(a) A parallel-channel band-reject circuit. (b) If ϖ
L
< ϖ
H
for the high-pass and
low pass characteristics in Fig. 5.2.8b, the band-reject response is obtained.

A notch response

A twin-tee network used to obtain a notch. If Y = 0, the notch
frequency and pole frequencies are equal. Inclusion of Y ≠ 0
converts the circuit to a high-pass or low-pass notch.