How to extract the constant phase of a sine wave?

Hello, I would extract the phase of a simple signal, for example a sine wave:

phase = pi/2;
x = sin(omega*t + phase);

I tried with

 P = angle(x)

but in this case, if I plot (t,P) I obtain a variable phase. I want the exact phase equal to pi/2, so a constant curve. Do you know how to do it?

Answer 1

[Honglei Chen]

Do you know omega? If so, you can do something like this

fc = 10;
omega = 2*pi;
t = (0:9)/10;
p = pi/2;
x = sin(omega*t+p);
xc = hilbert(x);
xcref = hilbert(sin(omega*t));
P = mean(angle(xc.*conj(xcref)))

Here I'm using analytic signal to simplify the math a bit. you can also do it in real domain but then you need a low pass filter to remove the unwanted frequency after mixing.

HTH

Answer 2

[David Sziroczak]

If it's such a simple function you are after, wouldn't it be possible just to simply extract value of the function at t=0 or pi or similar, and get the angle from asin?

Other idea, you could do a complex FFT and work it out from that?

Hope this helps,

David