Page 224 - Analog and Digital Filter Design

Bandstop Filters 22 1

J = zero frequency.

fR2R
R6=- when fR >.fx or when fR < f-.
fz
R6 = R when an all-pole filter is required, since fR = f- and R5 is not connected
(see the State Variable Bandstop Filters section).

The resistors labeled R and R’ can be any arbitrary value; a typical value may
be in the range 1 kQ to 100 kQ; say 10 kQ. The resistors labeled R have an effect
on the input impedance of the filter section. The value of R should be several
times higher than the input signal’s source impedance.

Denormalization oi Bandstop Biquad Filter Section

Consider a hypothetical design for a Cauer filter section that will produce a pole
and a zero. This design has a pole fR = 280rad/s, which has Q = 15. The zero for
this design will be at 300radk

Let C=O.l,uFandletR=R’= 10kQ.

R6=-=8711Q.
fR2
fi

Reference

i. Williams, A., and E J. Taylor. Electronic Filter. Des@ Handbook. New
York: McGraw-Hill, 1988.

Exercises

7. I Describe the step-by-step process for designing a passive bandstop
filter, starting with a lowpass prototype.