ANALOG AND DIGITAL BUTTERWORTH FILTER DESIGN

Butterworth filter is designed to have passband and stopband as flat as possible. We implemented low pass Butterworth filter using Scilab. Attenuation in passband and stopband (AS,AP), passband and stopband frequencies(fS,fP) and sampling frequency(FS) were taken as inputs. First we designed analog filter from the inputs and then digital filter was designed from the analog filter. We got magnitude plot and pole-zero plot for both analog and digital filters in th output.

We observed that as we increase the order of the filter, magnitude plot becomes steeper in the transition band and we get more idealized plot. As all poles were inside the unit circle, the filters were stable.

As shown in the figure, for order N=11, we get response which tending to ideal one.

https://drive.google.com/drive/folders/0BwJUrR8ne7NkMkREVm9oSS1nZEU