Title: Digital click removal and squelch control circuit for an FM receiver

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Abstract: A digital click removal and squelch control circuit for a digital FM receiver. The digital receiver generates a series of binary number electrical signals each of which is representative of the instantaneous phase angle of a received frequency-modulated electrical signal or signal derived therefrom. The phase angle signals are differentiated to produce binary number electrical signals that represent the rate of change of phase angle, or, the instantaneous frequency of the received signal. During a given time interval, the phase change caused by the modulation of the received signal must be within a range determined by the bandwidth of the received frequency-modulated signal. Phase changes outside of this range represent electrical noise or clicks and are removed by the click removal circuit of the invention. If a predetermined number of clicks occur during a predetermined time interval, the squelch control circuit of the invention provides a squelch control signal which may be used to disable the output of the FM receiver. When the click rate decreases, the output of the FM receiver is restored.


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