What is the meaning of positive phase in a bode plot?

[kandelabr]

Homework Statement

I have a bode plot with a positive phase.

Homework Equations

this is a MATLAB code for the thing

% 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

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!

 

[DeeNos]

The phase in a bode plot refers to the phase shift between the input and output signals at different frequencies. In this case, the positive phase means that the output signal is lagging behind the input signal by a certain angle. This is represented by the positive slope of the phase curve in the bode plot. Therefore, the output signal is not coming before the input, but rather lagging behind it.