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Receiving reproducing system

  • US 4,380,824 A
  • Filed: 02/12/1981
  • Issued: 04/19/1983
  • Est. Priority Date: 04/18/1980
  • Status: Expired due to Fees
First Claim
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1. A receiving reproducing system comprising:

  • an antenna;

    a signal processing circuit connected to said antenna for providing a detected output signal from a radio-frequency signal which is received by said antenna;

    power amplifier means for amplifying the detected output signal of said signal processing circuit;

    a speaker connected to be driven by said amplified output signal;

    a variable gain circuit connected between said signal processing circuit and said power amplifier means;

    noise detector means for detecting the surrounding noise level of a sound field;

    received level detector means for detecting a level which is dependent upon the received signal level of said antenna; and

    control means connected between said noise detector means and said variable gain circuit, said control means controlling the gain of said variable gain circuit in case the output signal of said received level detector means is higher than a preset value so as to control the level of said amplified output signal in proportion to the surrounding noise level of said sound field in response to the output signal of said noise detector means and said control means forcibly lowering the level of said amplified output signal in case said output signal of said received level detector means is lower than said preset value;

    wherein said antenna includes an AM antenna and an FM antenna;

    wherein said signal processing circuit includes an AM tuner for obtaining an AM detected output signal from an AM radio-frequency signal which is received by said AM antenna, an FM front end for obtaining an FM intermediate-frequency signal from an FM radio-frequency signal which is received by said FM antenna, an FM intermediate-frequency signal processing circuit for obtaining an FM detected output signal from said FM intermediate-frequency signal, and an FM stereo demodulator enabled to obtain a left-channel demodulated output signal and a right-channel demodulated output signal from said FM detected output signal;

    wherein said power amplifier means includes a first power amplifier and a second power amplifier;

    wherein said speaker includes a first speaker and a second speaker which are driven by the output signal of said first power amplifier and the output signal of said second power amplifier, respectively;

    wherein said variable gain circuit includes a voltage-controlled attenuator having its signal transmission from a first input terminal to a first output terminal controllable by a control voltage, which is to be impressed upon a first control input terminal, and its signal transmission from a second input terminal to a second output terminal controllable by a control voltage which is to be impressed upon a second control input terminal, the first input terminal and the second input terminal of said voltage-controlled attenuator being selectively fed with either the AM detected output signal, which is obtained from said AM tuner, or the left- and right-channel demodulated output signal which are obtained from said FM stereo demodulator by way of a selection means, the first output terminal and the second output terminal of said voltage-controlled attenuator being connected with an input terminal of said first power amplifier and an input terminal of said second power amplifier, respectively;

    wherein said received level detector means includes a tuning meter circuit in said AM tuner and a tuning meter circuit in said FM intermediate-frequency signal processing circuit;

    wherein said control means includes a voltage comparator to be fed with a tuning meter drive voltage from one of said tuning meter circuits and a reference voltage which corresponds to said preset value wherein said control means further includes a change-over switch having a first input terminal connected to receive the output voltage of said noise detector means, a second input terminal connected to receive a control voltage for forced attenuation, and output terminals connected to the first and second control input terminals of said voltage-controlled attenuator; and

    wherein the output of said voltage comparator controls said change-over switch, in case said tuning meter drive voltage is higher than said reference voltage, to impress the output voltage of said noise detector means upon the first and second control input terminals of said voltage-controlled attenuator, and impresses said control voltage for forced attenuation upon the first and second control input terminals of said voltage-controlled attenuator in case said tuning meter drive voltage is lower than said reference voltage, thereby disabling sound field effects on said power amplifier output signals.

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