| 摘要 |
PURPOSE:To prevent the intrusion of oscillation signals sent from a local oscillation part and to simplify the constitution of an AM radio receiver, by providing an LPF which can transmit signals up to an intermediate frequency between an intermediate frequency amplifying part and an AM wave detecting circuit or into this AM wave detector. CONSTITUTION:The signal converted into an intermediate frequency by a frequency converting circuit, etc. is applied to an input terminal 2 and then amplified by an intermediate frequency amplifying part 4. An LPF6 which transmits signals up to an intermediate frequency is set at the stage following the part 4. The intermediate frequency signal passed through the LPF6 is applied to an AM wave detecting circuit 8. Hereafter the wave detection output is applied to a low frequency amplifying part from a terminal 10. The LPF6 consists of a monolithic IC together with the part 4 and the circuit 8. Thus the signal lower than an intermediate frequency to undergo wave detection is applied to the circuit 8. This prevents the intrusion of a local oscillation frequency component and a short wave band. |
