| 摘要 |
PURPOSE:To enable automatic channel selection with high precision and also to simplify a circuit by making use of a multiplier circuit, constituting an FM detection circuit, as a tuning detection circuit for AM reception, by adding a function of selective operating on arrival of an AM intermediate frequency signal to the multiplier circuit. CONSTITUTION:As a phase shift circuit constituting FM detection circuit 4, a circuit is used which phase-shifts selectively both an FM intermediate frequency signal and AM intermediate frequency signal by 90 deg., and the AM intermediate frequency signal is applied selectively to the input of FM limiter amplifier 3 or FM detection circuit 4 to put the detection circuit and tuning detection circuit 6 into operation in FM and AM receptions, so that it will be used as part or all of a stop signal during automatic channel selecting operation. As a result, while the circuit is simplified, accurate AM automatic channel selection can be brought to effect by making use of the FM detection circuit as a tuning detection circuit in AM reception. |
