| 摘要 |
PURPOSE:To obtain an AGC effect without using an AGC amplifier by applying a control voltage outputted from a DC amplifier of an FM discriminator so as to constitute a negative feedback loop. CONSTITUTION:Part of an output of demodulation signal is fed to a level detector 5, from which a detection voltage proportional to a demodulation signal level is obtained, the voltage is compared with a reference voltage 6 and amplified, the comparison output voltage is fed to a control voltage application terminal 8 of the FM discriminator 2 to constitute a feedback circuit. The voltage outputted from the DC amplifier 7 has a value in correlation with the level of the demodulation signal and varies with the signal level. When the output voltage is fed to the control voltage application terminal 8 while being varied, the resonance frequency and its Q of the frequency discriminator circuit in the FM discriminator 2 are varied and the demodulation sensitivity as the FM discriminator is varied. Thus, it is possible to keep the level of a base band signal output at a demodulation output terminal 4 constant. |
