Asynchronous digital frequency shift keyed (FSK) signals are demodulated by using an autocorrelation type demodulator including digital integration. To this end, the autocorrelation function and digital integration are realized by generating integration increments, i.e., area increments, at the digital...http://www.google.com.hk/patents/US4479092?utm_source=gb-gplus-share專利 US4479092 - Digital frequency-shift keyed demodulator
