How to extract the constant phase of a sine wave?

Question

Alessandro Longo 2017-11-7

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回答： David Sziroczak 2017-11-9

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?

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Answer 1

Honglei Chen 2017-11-7

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在 MATLAB Online 中打开

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

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Answer 2

David Sziroczak 2017-11-9

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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