FM DEMODULATOR

专利名称：FM DEMODULATOR发明人：JOSEPH REED申请号：AU9154482申请日：19821215公开号：AU9154482A公开日：19830804

摘要：A demodulator of the type employed in a \"zero-IF\" system uses a local

oscillator for providing guadrature output signals at the center frequency of an FM signalto be demodulated. The demodulator has first and second mixers for separately mixingthe FM signal with the quadrature signals to provide a first and second output signal eachin quadrature at the outputs of said mixers. These signals are low pass filtered. Thedemodulator includes third and fourth mixers with each mixer receiving at an input one ofthe low pass signals. At another input the mixers receive third and fourth signals. Thethird and fourth signals are derived from mixing a variable controlled oscillator (VCO)signal with the local oscillator guadrature signals. The outputs of the third and fourthmixers are applied to the inputs of a difference amplifiers, the output of which controlsthe frequency of the VCO in an automatic frequency control mode (AFC) to cause theoutput of the difference amplifier to provide demodulated signal. A switching meansoperates to alternate the third and fourth signals as applied to the input of the third andfourth means as well as the output as applied to the difference amplifier to cause anadditional amplifier coupled to the outputs of the mixers to provide a DC control signalused for automatic gain control.

申请人：INTERNATIONAL STANDARD ELECTRIC CORP.

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