Can't comment without a circuit diagram
Also.

You can do all you want with a fast 8052, your A/D and lots of code, or Amplitude phase and frequency can be measured with an 8052 and ADC, provided you prcondition the signal.

Amplitude: For accuracy, I suggest you use a simple perfect rectifier to hold the peak level of your signal, which you can then sample at will.

Your phase measurement is derived from comparing the timing of a reference clock againat a signal that has been passed through a comparator. Use the falling edge of your ref to start a timer, use the falling edge of the signal of interest to stop it.

Frequecny can be done by simple period measurements.

Steve