[Filter] Analog filter to Digital filter

Analog filter can be converted to digital filter (IIR Filter) by bilinear transformation.

Bilinear transformation, Pre-warping to compensate cut-off frequency

Download

---------------------------
Design butterworth filter using Matlab function 'butter' (Signal Processing Toolbox)
To use this, signal processing toolbox license is necessary.

[b, a] = butter(order, W, filter type)

# Filter type
1. LowPass Filter = 'low'
2. HighPass Filter = 'high'
3. Bandstop Filter = 'bandstop'
4. Bandpass Filter = 'bandpass'

For example, 6th order lowpass filter

fc = 300;　% cut-off frequency
fs = 1000; % sampled data (sampling frequency)

[b,a] = butter(6,fc/(fs/2));
freqz(b,a)