design LPF using Filter with Butterworth

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Mohamed Abdulwahab
Mohamed Abdulwahab 2017 年 4 月 24 日
回答済み: Binaya 2024 年 10 月 10 日
how should i use an analog filter with a Butterworth response of order 3, to design a digital IIR low pass filter with 3dB cutoff angular frequency 0.2pi
the aim is to plot the magnitude and the phase response and i knew that i should use butter , freqz , angle functions

回答 (1 件)

Binaya
Binaya 2024 年 10 月 10 日
Hi Mohamed
You can follow the below steps to create a lowpass Butterworth filter:
  1. Setup the parameters for Butterworth filter i.e. order, cut-off frequency and filter type.
  2. Create a Butterworth filter using "butter" function: https://www.mathworks.com/help/signal/ref/butter.html
  3. Use "freqz" function to find the frequency response of the filter: https://www.mathworks.com/help/signal/ref/freqz.html
I have also provided an exampe code for you to refer:
N = 3; % 3rd-order Butterworth filter
Wn = 0.2; % Normalized cutoff frequency (0.2 corresponds to 0.2*pi radians/sample)
filterType = 'low'; % Lowpass filter
[b, a] = butter(N, Wn, filterType);
numPoints = 1024; % Number of frequency points
[H, w] = freqz(b, a, numPoints, 'whole'); % Compute frequency response
You can refer to the following MATLAB Answers post for more details on how to plot the frequency response: https://www.mathworks.com/matlabcentral/answers/588133-magnitude-and-phase-response-of-a-lowpass-filter?s_tid=srchtitle
Hope this helps

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