Fm demodulator with carrier shift compensation

Claim 1

An FM demodulating circuit arrangement comprising: an input for receiving an FM signal to be demodulated; delay means coupled to said input for delaying the received FM signal by a preset time delay; a signal combining circuit coupled to said input and to said delay means for combining the delayed and undelayed FM signals so as to derive a combined signal having a mean value which is proportional to the frequency of the received FM signal; and filter means coupled to said signal combining circuit for filtering the combined signal to derive the mean value thereof, such filtered signal constituting a demodulated signal the amplitude of which corresponds to the frequency of the received FM signal; characterized in that: said demodulating circuit arrangement further comprises a datum level detection circuit coupled to said filter means to receive the demodulated signal, detect a selected datum level thereof, and provide a control signal corresponding to said datum level to said delay means; and the preset time delay of said delay means is adjustable by said control signal, thereby adjusting the proportionality factor between the frequency swing of the FM signal and the amplitude of the demodulated signal, so as to maintain a substantially constant value of said datum level of the demodulated signal; whereby the maximum amplitude of the demodulated signal is stabilized relative to said datum level thereof despite variations in the maximum frequency swing of the FM signal.