An FSK demodulation circuit especially suited for integrated construction is provided. The demodulating circuit uses N counters and a counter selector circuit for sequentially switching the counters at every zero-cross point in the received FSK signal. Sensitivity of demodulation is improved by N-time...http://www.google.de/patents/US4517519?utm_source=gb-gplus-sharePatent US4517519 - FSK Demodulator employing a switched capacitor filter and period counters
