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Homework Help: Bode plot: positive phase

  1. Mar 4, 2012 #1
    1. The problem statement, all variables and given/known data
    I have a bode plot with a positive phase.

    2. Relevant equations
    this is a matlab code for the thing
    Code (Text):
    % bode phase plot
    w = logspace(1, 4, 100);
    G = 100*(1+0.017i*w)./(1i.*w.*(1+0.05i.*w).*(1+0.0025i.*w).*(1+0.001i.*w));
    fi = atand(imag(G)./real(G));
    semilogx(w, fi); % x-axis: log(omega*j), y-axis: phase in degrees
    3. The attempt at a solution
    Nothing to solve, there's just one thing I don't get: if phase means "relation between input and output signal", how can output signal come before the input?
     
    Last edited: Mar 4, 2012
  2. jcsd
  3. Mar 4, 2012 #2
  4. Mar 4, 2012 #3

    gneill

    User Avatar

    Staff: Mentor

    Keep in mind that the signals being compared are not starting from some t=0. They are a depiction of some steady-state relationship between theoretically eternal sinusoids, and as such can exhibit a relative phase shift.
     
  5. Mar 5, 2012 #4
    yeah, i thought this would be the explanation, and i neglected that bode plot is steady-state only.

    thanks!
     
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