| 摘要 |
SELECTIVITY A double-tuned circuit of a tuner that can be switched for tuning to a plurality of frequency bands by turning a switching diode ON or OFF restrains degradation of a selectivity caused by an undesirable additional tuning circuit or parasitic tuning circuit formed by a capacitance generated when the switching diode is OFF and inter- terminal capacitance of a resistor. A double-tuned circuit of a tuner is also provided that exhibits good selectivity with reduced damping to a tuning circuit in a low-band receiving mode, and also exhibits a wider tuning range. A feed resistor for high-band receiving is directly connected to a switching diode in a primary tuning circuit, and the feed resistor for high-band receiving is connected to a switching diode via a coil in a secondary tuning circuit. Hence, the tuning frequency of a parasitic tuning circuit in the primary tuning circuit is lower than the tuning frequency of a parasitic tuning circuit in the secondary tuning circuit, so that the peak of a frequency characteristic generated by the parasitic tuning circuit can be reduced. As a result, the interference with intermediate frequency signals can be reduced.
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