MATLAB: How can i plot the magnitude and phase response for given output

digital signal processingsignal processing

Best Answer

First, code the function you posted an image of. It would be best to create it as a transfer function object, using the tf function. See the relevant documentation for details.

Then, use the bode (link) or lsim (link) functions, depending on what you want to do.

Note that for a SISO system, you will have to use squeeze to plot the result, if you want to plot the outputs of bode and the others.

Example —

[mag,phase,wout] = bode(tfobj);
figure(3)
subplot(2,1,1)
semilogx(wout, 20*log10(squeeze(mag)), '-b', 'LineWidth',1)     % Bode Plot: Magnitude
ylabel('H(f) (dB)')
grid
subplot(2,1,2)
semilogx(wout, squeeze(phase), '-b', 'LineWidth',1)             % Bode Plot: Phase
xlabel('Frequency (rad/sec)')
ylabel('Phase (°)')
grid

Related Solutions

MATLAB: How to plot this

It depends on the Toolbox you’re using.

For a filter using the Signal Processing Toolbox, use the freqz (link) or freqs (link on the freqz page) functions.

For a control system using the Control System Toolbox, use the bode (link) function. Note that it is essentially impossible to change any of the plot characteristics using bode, so if you want to customise the plot, get the outputs from bode and plot them using the subplot function.

MATLAB: Change marker width in bode plot

The bode function doesn’t accept many options with respect to its plots. The easiest way to do what you want is to request at least the first three outputs of the bode function, and then plot them using subplot and plot. The plots are the same as any other plot object:

[mag,phase,wout] = bode(sys);
subplot(2,1,1)
plot(wout, mag)
subplot*2,1,2)
plot(wout, phase)

Use ‘20*log10(mag)’ to plot the magnitude in decibels, and semilogx instead of plot to make the plot look like those bode produces on its own:

[mag,phase,wout] = bode(sys);
subplot(2,1,1)
semilogx(wout, 20*log10(mag))
subplot*2,1,2)
semilogx(wout, phase)

Best Answer

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