FM and FSK demodulator with automatic frequency control AFC for receiving frequency modulated and frequency shift keying signals

摘要

The FM/FSK demodulator has a coincidence demodulator which includes a capacitor (1), a multiplexer (2), a low pass filter (3) and an resonance loop (4-9). The coincidence demodulator is automatically tuned to the current value of the intermediate frequency of the signal to be demodulated. By use of a feedback coupling, the constant component of the demodulator output signal can be used for directly controlling a varactor diode (8) providing frequency compensation without regulation of external circuits.