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3db bandwidth of a low pass filter

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Ratna
Ratna 2011-9-22
回答： Satish reddy Kotamreddy 2017-12-6
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?

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采纳的回答

Wayne King
Wayne King 2011-9-22
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

更多回答（2 个）

Wayne King
Wayne King 2011-9-22
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
Satish reddy Kotamreddy
Hi i need matlab script for operational trans conductance amplifier lowapass with 3db frequency of 1mhz

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