Phase Compansation Circuit

Hi, I have a system which two signals must have 90 degree phase difference . I am measuring their phase difference using mixer(both signals at the same frequency and other harmonics are filtered). I have a phase shifter to adjust phase of one of them. Phase shifter is voltage controlled. My question is what kind of circuit can be used to minimize voltage output of the mixer. Some kind of opamp integrator circuit in a closed loop maybe ?

Since i can't know which signal is lagging or leading, sometimes i must shift phase further, right ?

A PI error amplifier would be my first guess.

You didn't tell about the phase shifter range. Generally, an additional comparator for positive or negative phase difference and phase reversal switch are required to push the phase difference to the right part of the detector curve.

Thanks for reply. Phase shifter range is 0-600 Degree for 0V - +5V analog voltage. (120 deg/volt). I didn't understand how can we know which signal is leading using comparator after mixer output . I will study some PI error amplifiers. Looks like thats what i need.

That's not possible. You need to check the phase relation of the input signals, e.g. with a DFF.