Determine the critical frequency of the Sallen-Key low-pass filter in Figure, and set the value of R_{1} for an approximate Butterworth response. | Holooly.com
Sallen–Key topology - Wikipedia
Sallen-Key Low-pass Filter Design Tool
Low-Sensitivity Sallen-Key Filter Design with the HP-41C Programmable Calculator
Third order Sallen Key Lowpass Fractional Filter. | Download Scientific Diagram