Patent ID: 8509717

Claim:
A frequency modulation receiver, comprising: an automatic frequency controller, receiving a demodulated frequency modulation signal demodulated from a radio frequency signal and outputting a control voltage to control an oscillation frequency of a local oscillator according to the demodulated frequency modulation signal; and a signal detector coupled to the automatic frequency controller, receiving the control voltage and determining whether the radio frequency signal is a frequency modulation signal according to the control voltage and a predetermined voltage range, wherein the signal detector further comprises: an average circuit coupled to the automatic frequency controller, receiving the control voltage and outputting an average value of the control voltage; and a voltage comparator coupled to the average circuit, wherein the voltage comparator determines that the radio frequency signal is the frequency modulation signal when the average value is within the predetermined voltage range, and the voltage comparator determines that the radio frequency signal is not the frequency modulation signal when the average value is not within the predetermined voltage range, wherein the voltage comparator further comprises: a first operational amplifier coupled to the average circuit, outputting a first comparing result according to the average value and a first reference voltage; a second operational amplifier coupled to the average circuit, outputting a second comparing result according to the average value and a second reference voltage; and a AND logic gate coupled to the first operational amplifier and the second operational amplifier, outputting a determining signal to indicate whether the radio frequency signal is the frequency modulation signal according to the first comparing result and the second comparing result.