PURPOSE: To attain phase tracking type FM demodulation having no problem even when fluctuation of a power supply voltage takes place by employing a quadrature FM demodulation IC so as to attain phase tracking type FM demodulation and giving a compensation voltage to a voltage controlled varactor diode so as to compensate a compensation voltage.
CONSTITUTION: The circuit employs a quadrature FM demodulation integrated circuit comprising a phase comparator 7, a tracking filter 9 connects to a phase shift circuit connection terminal In3 of the integrated circuit and a signal is fed to other input terminal of the phase comparator 7 via a loop filter 8 and a tracking filter 9 from an FM demodulation output terminal Out1 to constitute a feedback control circuit. Then a compensation voltage generator 6 applying a compensation voltage for power supply voltage fluctuation is provided to one terminal of a voltage controlled varactor diode CD being a component of the tracking filter 9. Thus, even when the quadrature FM demodulation IC is employed, fluctuation of a DC level at the demodulation output terminal Out1 is lost against the fluctuation of the power supply voltage and the phase tracking FM demodulation circuit 1 suitable for the IC is realized.
MIZUNO KENICHI
OKUAKI KATSUO
