| 摘要 |
PURPOSE:To compensate a shift of a center frequency caused by an environmental variation by adding an automatic frequency control operation to a reference crystal oscillating circuit of a synthesizer PLL circuit. CONSTITUTION:When a turner device is in a prescribed tuning state, a switching circuit 32 applies an AFC voltage from an FM detecting circuit 10, to an oscillating circuit 30, and an oscillation frequency of the oscillating circuit 30 is controlled by the AFC voltage. As a result, a center frequency is changed in accordance with the AFC voltage, and adjusted by following a deterioration of various characteristics based on an environmental variation, for instance, a variation of the center frequency corresponding to a characteristics variation of an IF filter of an intermediate frequency amplifying circuit 8 and an FM detecting coil. As a result, a stable tuning state can be maintained, and also an FM detecting band can be expanded equivalently.
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