| 摘要 |
PURPOSE:To decrease noise at no input or a weak input by applying feedback to a selective amplifier of an FM receiver. CONSTITUTION:The selective amplifier 1 and an attenuator 3 feeding back the output of the amplifier to an input of the amplifier 1 while attenuating it are formed so as to oscillate a signal in a prescribed frequency near the center frequency f0 of the amplifier 1. The feedback quantity of the attenuator 3 is set so that the output of the amplifier 1 is just saturated when no signal input is given from an input terminal IN. Then the output of the amplifier 1 is saturated at an oscillation frequency near the frequency f0 and other frequency component is suppressed. In inputting the output to an FM detector 2, a prescribed voltage whose noise is suppressed is outputted to an output terminal OUT. Thus, noise at no input or a weak input is reduced.
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