Butterworth filter
= Butterworth filter
{c}
A maximally flat passband magnitude design. A normalized second-order low-pass denominator is $1+\sqrt2s/\omega_0+s^2/\omega_0^2$. An equal-component <Sallen-Key low-pass filter> realizes this damping when $K=3-\sqrt2$, with the corresponding non-inverting passband gain.