FSK time-delay demodulator with reduced DC-offset.

摘要

An improved multilevel FSK demodulator, according to the invention, is provided that down-converts the IF frequency back to baseband quadrature via dual mixers. The improved multilevel FSK demodulator uses controllable time-delay in the demodulation process. This method requires a 90 DEG phase difference between 2 modulated signals to produce a maximum demodulated output amplitude at the maximum frequency deviation. Since the IF frequencies have been down-converted back to baseband quadrature, these 2 signals are only "out of phase" by an amount DELTA t that is equal to 90 DEG /d omega . A further aspect of this invention addresses minimizing the DC offset from the demodulator by providing a feedback signal which controls the amount of delay provided to one of the quadrature signals.