An input circuit for an AM/FM radio receiver having an FM intermediate
frequency rejection circuit and an AM image frequency rejection circuit,
an FM input circuit for receiving frequency-modulated input signals and an
AM input circuit for receiving amplitude-modulated input signals, and PIN
diodes are provided for switching from AM operation to FM operation
between the FM intermediate frequency rejection circuit and the AM image
frequency rejection circuit. The PIN diodes connect the FM intermediate
frequency rejection circuit for high-frequency signals to ground when FM
operation is selected, and a control voltage is applied to the switching
device for providing automatic gain control between the FM intermediate
frequency rejection circuit and the AM image frequency rejection circuit
when AM operation is selected.
