8th order sallen-key butterworth lowpass filter

Papabravo

Joined Feb 24, 2006
19,576
I did a quick hand calculation with the Butterworth transfer function to determine the filter order so I assume that it is basically the same but with the Chebyshev transfer function, is that correct?
As long as you take account of the value of ε implied by your selection of 0.1 dB ripple in the passband
 

LvW

Joined Jun 13, 2013
1,586
I do not know about the "direct" realization and will try to find out more about it but if you have literature suggestions I will be very happy to read up on them.
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The circuit is the last one in my original post, there is no option to choose passive realization.
* I cannot understand why the last 4-stage filter in your original post contains one 2nd-order stage (the 1st one) which uses a passive RLC lowpass. Why not a S&K stage like the other three?

* For "direct realization" of a 8th-order lowpass you should consult some relevant textbooks (dealing with filter theory) or use some of the following keywords for a google search:
FDNR technique, Bruton Transformation, Leapfrog topology, Follow-the-Leader (FLF), Primary Resonator Block (PRB)
 
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