# Tag Info

Accepted

### Why don't unit circle poles lead to infinite amplitude response for Butterworth lowpass?

You've made an understandable mistake. You are probably looking at this picture: That is not the unit circle, and it isn't even in the $z$ domain. What you are looking at is the locations of the ...
• 8,131
Accepted

### Specify notch bandwidth by pole placement

Summary Given the equation for the transfer function of the second order notch filter:  H(z) =\frac{1+2\alpha \cos(\omega_n)+\alpha^2}{2+2\cos(\omega_n)}\frac{z^2-2z\cos\omega_n+1}{(z^2-2az\cos\...
• 36.1k
I suspect that $G(s)$ is the Open Loop Gain. The root Locus would be the location of the poles in the Closed Loop Gain as you vary $K$. The poles in the Closed Loop Gain are given by the roots of the ...