Question 9.3: Determine the critical frequency of the low-pass filter in F...

Since R_A=R_B=1.0  \mathrm{k} \Omega \text { and } C_A=C_B=0.02  \mu \mathrm{F},

f_c=\frac{1}{2 \pi R C}=\frac{1}{2 \pi(1.0  \mathrm{k} \Omega)(0.02  \mu \mathrm{F})}=7.96  \mathrm{kHz}

For a Butterworth response, R_1 / R_2 = 0.586.

R_1=0.586 R_2=0.586(1.0  \mathrm{k} \Omega)=\mathbf{5 8 6}   \Omega

Select a standard value as near as possible to this calculated value.

PRACTICE EXERCISE

Determine f_c for Figure 9–11 if R_A=R_B=R_2=2.2   \mathrm{k} \Omega \text { and } C_A=C_B= 0.01  \mu \mathrm{F}. Also determine the value of R_1 for a Butterworth response.