Muting arrangement of a radio receiver with a phase-locked loop frequency synthesizer

Claim 1

A radio receiver comprising: a signal transmission path including a mixer circuit for converting a radio-frequency signal into an intermediate frequency signal, an intermediate frequency amplifier for amplifying said intermediate frequency signal, and a detection circuit for demodulating said intermediate frequency signal; a local oscillator circuit means having a phase-locked loop comprised of a voltage-controlled oscillator for providing a local-frequency signal to said mixer circuit, a frequency divider for dividing the output frequency of said voltage-controlled oscillator, a reference signal generator to produce a reference frequency signal, a phase comparator for comparing in phase said reference frequency signal with the output signal of said frequency divider, and a loop filter connected between said phase comparator and said voltage-controlled oscillator for supplying said voltage-controlled oscillator with a control voltage signal having a magnitude which is a function of the phase difference between the input signals of said phase comparator; a non-lock detection circuit means connected to the output of said phase comparator for detecting a non-lock state of said phase-locked loop in which the output signals of said frequency divider and said reference signal generator are not coincident in phase; and mute gate circuit means provided at the output side of said detection circuit of said signal transmission path of the receiver and responsive to said non-lock detection circuit means to mute the demodulated output signal at said signal transmission path, thereby interrupting production of an audio signal from the output of the receiver when the output signals of said frequency divider and signal reference signal generator are not coincident in phase.