Direct conversion FSK demodulator.

摘要

An FSK demodulator for demodulating first and second baseband signals obtained from a received frequency shift keying signal, the first and second baseband signals having a quadrature relation therebetween, a lead and lag relation between the first and second baseband signals being changed in accordance with frequency shift from a carrier frequency of the frequency shift keying signal, comprises: a voltage change judging circuit for judging whether a magnitude of the first baseband signal increases or decreases within a predetermined interval; and an inverting circuit responsive to an output of the voltage change judging circuit and the second baseband signal for outputting a demodulated signal produced by inverting the second baseband signal in accordance with the output of the voltage change judging circuit. In addition, a second voltage change judging circuit and a second inverting circuit and a combining circuit for combing the results of said first and second inverting circuits may be provided to improve noise resistance. Inflection points in the baseband signal are detected to select one output from the first, second inverting circuit and the combing circuit in accordance with detection of the inflection points. <IMAGE>