Need help improving the Caller ID FSK demodulation circuit
Not sure on the exact requirements for FSK and caller ID, but if this is anything like ~50kHz data over power line systems, Design guides often suggest a 4th order LC bandpass filter as a cheap starting point.

This should be simple enough to test out.







simulate this circuit &ndash; Schematic created using CircuitLab



Notes:


This is a starting point. R1 may need adjustment depending on how much your circuit loads the filter etc. Good news is it is easy to simulate this, so you can rest out different values virtually.
You no longer need a blocking capacitor from your original circuit since C2 does that for you.
I believe this would take the place of R1 and the 22nF capacitor in the above circuits.


You might also not want to attach this circuit to ground, you would have to study how do you supporting passives I see on those inputs are set up. You will have to study more the purpose of R1, R4 and the surrounding components. They are tightly specified at 1% and I'm not sure why.