QA customer is building a FSK demodulator with the mark & space frequencies
being 18KHz & 20KHz respectively. They require an envelope detector for the
process, and have chosen the ADL5511. But, according to the guidelines
provided in its datasheet, high valued capacitors up to 0.68uF are required to
be connected at the FLT1, FLT2 & FLT3 pins. They are using separate envelope
detectors for mark & space frequencies, so differentiation between the two FSK
frequencies is the matter of concern.
AYou can operate the device with arbitrarily large capacitors. The best advice
is to purchase an evaluation board to test out whether you can effectively
demodulate the FSK signal in your application.