3db bandwidth of a low pass filter

Hi, I need to generate a low pass filter and find its 3db values. Do we have any matlab command to find 3db bandwidth? If so, can I plot it?

Answer 1

[Wayne King]

Another way is to get the magnitude response using freqz()

      [B,A] = butter(10,0.1);
      [H,W] = freqz(B,A);
      magresp = 20*log10(abs(H));
      maxresp = max(magresp);
      [I,~] = find(magresp < maxresp-3,3,'first');
      fprintf('3-dB point is %2.3f*pi radians/sample\n', W(I(1))/pi)

Wayne

[Vivek Bhadouria]

freqz is a nice function to see the response of the filter.

Answer 2

[Wayne King]

Hi, one way is to use an IIR design in MATLAB which uses the 3-dB point directly in the design of the filter. (FIR filters use 6-dB points).

For example:

d = fdesign.lowpass('N,F3dB',10,0.1);
Hd = design(d,'butter');
fvtool(Hd);

If you have the DSP System Toolbox installed, you are able to call the measure() method on Hd

measure(Hd)

Hope that helps,

Wayne

Answer 3

[Satish reddy Kotamreddy]

Hi i need matlab script for operational trans conductance amplifier lowapass with 3db frequency of 1mhz