Hi Guys, I am trying to build a circuit that will convert the phase difference of two signals into voltage. Since this is my first time to build this kind of circuit I don't have any idea on how to go about it. Can someone help me on this one...Thanks

 

You might find this tutorial on PLL's interesting. Especially the part about phase detectors - http://www.sentex.net/~mec1995/gadgets/pll/pll.html

 

Try using DSP processors.
I.e ADE7878.

 

A simple XOR gate makes an excellent phase detectors. So does a full wave diode bridge.