pll calibration
Do you mean you have 17 frequencies (all of them between 20KHz and 90KHz) let'us call them f1 to f17 ?
If it is so, my question remain: when your signal goes from one frequency to another frequency, this change in the frequency happens with a certain speed or cadence. That is what I mean by: " the frequency of the modulating signal".
If you know the exact valu of these 17 frequencies, you can opt for another solution:
You can make 17 different band pass filters each one tuned to one of these frequencies and followwed by an amplitude detector and a schmidt trigger. At the end of the circuit you have to draw a sort of DAC each input bit correspond to the outout of a schmitt trigger and has a weight different to the others.
good luck
And excuse me for my poor englich.