Question 9.8: Verify that the band-stop filter in Figure 9–25 has a center...

f_0 equals the f_C of the integrator stages.

f_0=\frac{1}{2 \pi R_4 C_1}=\frac{1}{2 \pi R_7 C_2}=\frac{1}{2 \pi(12~ \mathrm{k} \Omega)(0.22 ~\mu \mathrm{F})}=\mathbf{6 0 . 3 ~ H z}

You can obtain a Q = 10 by choosing R_6 and then calculating R_5.

Q=\frac{1}{3}\left(\frac{R_5}{R_6}+1\right) \quad R_5=(3 Q-1) R_6

Choose R_6 = 3.3 kΩ. Then

R_5=[3(10)-1] 3.3 ~\mathrm{k} \Omega=95.7~ \mathrm{k} \Omega

Choose 100 kΩ as the nearest standard value.

PRACTICE EXERCISE

How would you change the center frequency to 120 Hz in Figure 9–25?