With the Sallen Key filter pictured below, I'm designing a 3-4th order LP filter. This filter is supposed to have variable adjustment so that I can block frequencies higher than 250Hz all the way up to ones higher than 1000Hz. I'm getting frustrated though because I can't figure out how to select my component values.
I assume that:
- cascading this circuit 2 times should make this a 4th order LP filter
-Picking 2 random values for C1 and C2 and utilizing a variable resistor in place of R1 or R2 in each of the 2 levels will allow me to adjust to the values I mentioned earlier
-The equation for the cutoff frequency of this circuit is:
- Since I know the above equation, I can place in the frequency I want the limits at (250-1000Hz) for f0 in the equation and then solve for R1 or R2
What I can't figure out is this. How do I know what values to select for the 2 capacitors and one of the resistors such that as I rotate my variable resistor, the frequency ranges I want to block are attained?
I've been mixing and matching values for awhile and I'm getting nowhere doing it this way. There's gotta be a smarter way to go about doing this....
I assume that:
- cascading this circuit 2 times should make this a 4th order LP filter
-Picking 2 random values for C1 and C2 and utilizing a variable resistor in place of R1 or R2 in each of the 2 levels will allow me to adjust to the values I mentioned earlier
-The equation for the cutoff frequency of this circuit is:
- Since I know the above equation, I can place in the frequency I want the limits at (250-1000Hz) for f0 in the equation and then solve for R1 or R2
What I can't figure out is this. How do I know what values to select for the 2 capacitors and one of the resistors such that as I rotate my variable resistor, the frequency ranges I want to block are attained?
I've been mixing and matching values for awhile and I'm getting nowhere doing it this way. There's gotta be a smarter way to go about doing this....
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