Butterworth Filter

All poles lie on the left half plane equally distributed on a half circle with radius $\Omega =2\pi F$ which is shown above. The Butterworth filter is by far the most popular filter. Here are its properties:

• monotonic frequency response
• only poles, no zeros
• the Poles have analytical solution and very easy to calculate
• no constant group delay but usually acceptable deviation from a strict constant group delay for many applications.