| 摘要 |
PURPOSE:To obtain the FM demodulating circuit easy to adjust by adjusting the oscillation frequency of a voltage controlled oscillator by the common-mode signal level of a DC amplifier and obtaining the voltage comparison output from a voltage comparator. CONSTITUTION:The voltage of a voltage power source 22 of a DC amplifier 15 is so adjusted that the oscillation frequency of a voltage controlled oscillator 18 matches with the center frequency of the second intermediate frequency in the balanced state of the DC amplifier 15. Next, a differential balance adjusting circuit 14 performs such adjustment that the oscillation frequency of the oscillator 18 matches with the center frequency of the second intermediate frequency when FM signals are not inputted to input terminals 10 and 11. Thus, the FM demodulating circuit is easily adjusted without adjusting the air-core coil of the voltage controlled oscillator 18. Then, phase differences between FM signals inputted to input terminals 10 and 11 and the output signal of the voltage controlled oscillator 18 are detected by a phase comparator 12. These detection signals are outputted as demodulated signals from output terminals 16 and 17 through a low pass filter consisting of DC amplifiers 13 and 15. |
