FM Receiving device

#1. Field of the Invention

#The invention relates to an FM receiver which receives FM broadcast waves for listening to FM broadcasts.

#2. Discussion of the Prior Art

#FIG. 1 is a circuit structural diagram illustrating one example of the FM receiver of this invention.

#FIG. 2 is a circuit structural diagram illustrating another example of this invention.

#A description of the invention follows with reference to the figures. FIG. 1 illustrates the circuit structure of the FM receiver. In the figure, 1 is the antenna which receives FM broadcast waves. The FM broadcast wave (FM broadcast signal) received by this antenna 1 is amplified by the high frequency amplifier 2. This signal together with the output signal from the first local oscillator 3 are sent to the first mixer 4, where they are converted into the first intermediate frequency signal. This first intermediate frequency signal is then amplified by the first intermediate frequency amplifier 5' and then sent to the second mixer 7 with the output signal from the second local oscillator 6, where they are converted into the second intermediate frequency signal. This second intermediate frequency signal is then sent to the FM detector 8, and the FM detected output is then sent to the stereo demodulator 9, where it is separated into left and right signals. These separated signals are amplified at output amplifiers 10.sub.1, 10.sub.2, and brought to the output terminals 11.sub.1, 11.sub.2.

#The above is a description of the main constituent elements of the FM receiver. The receiver has a double conversion super heterodyne structure, but this FM receiver also has the following structure. Specifically, only the direct current component is selected from the output of the FM detector 8 by resistor 12 and condenser 13. This direct current component is fed back to said second local oscillator 6. The oscillation frequency of this second local oscillator 6 is controlled by the direct current component which was fed back.

#In this structure, when direct current voltage develops in the output of the FM detector 8 during tuning and, more precisely, in the vicinity of the correct tuning point of an FM station, this direct current voltage is fed back to the second local oscillator 6. The oscillation frequency of the second local oscillator 6 is controlled by the feed back direct current voltage so that the direct current voltage becomes substantially zero in the output of the FM detector 8 which carries out frequency-voltage conversion. This feed back control takes place in an instant. Thus, the formation of direct current voltage is substantially prevented in the output of the FM detector 8 by the direct current voltage feed back loop.