Bode plot: positive phase

kandelabr

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:

% 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?

kandelabr

OK, so i forgot G >> 20*log(G), and so the diagram is wrong, but still, the question remains the same - see this diagram:

http://en.wikipedia.org/wiki/File:Bode_High-Pass.PNG

gneill

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.

kandelabr

yeah, i thought this would be the explanation, and i neglected that bode plot is steady-state only.

thanks!

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kandelabr	OK, so i forgot G >> 20*log(G), and so the diagram is wrong, but still, the question remains the same - see this diagram: http://en.wikipedia.org/wiki/File:Bode_High-Pass.PNG

gneill Recognitions: Homework Help	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.

kandelabr	Bode plot: positive phase yeah, i thought this would be the explanation, and i neglected that bode plot is steady-state only. thanks!