veronjr:
I need to output a dc voltage based on the phase difference between two signals.
This sounds like a job for superman!!!
Actually..... you are probably referring to what they call a 'phase detector' of some sort.
Some kind of asynchronous logic circuit that outputs a positive square pulse when a slave signal lags the reference (up to some amount). The width of pulse equal to the time difference between signals. And output a negative pulse if slave signal leads (up to some amount). This is assuming that one of those square wave signals can always be the reference......while the other one is a slave signal.