Patent ID: 6020784
Filing Date: 2000-02-01
Classification: H03D

Abstract:
An FM demodulation circuit wherein a demodulation sensitivity thereof is raised when a level of a frequency modulated input signal drops, comprising:a phase conversion circuit for outputting a first output signal having the same phase as that of the input signal and a second output signal obtained by converting a frequency variation of the input signal into a phase variation, said phase conversion circuit allowing variation of a characteristic of the phase variation with respect to the frequency variation;a multiplier for outputting a signal of a phase difference between the first output signal and the second output signal outputted from said phase conversion circuit;a low-pass filter for integrating the output signal of said multiplier to form a demodulation signal and outputting the demodulation signal;an electric field strength detection circuit for detecting a level of the input signal; anda control current source circuit for outputting, when the level of the input signal detected by said electric field strength detection circuit drops lower than a predetermined level, control current to vary the characteristic of the phase variation with respect to the frequency variation to raise the demodulation sensitivity.