Double-tuned circuit of tuner featuring restrained degradation of selectivity

A double-tuned circuit of a tuner, comprising:

• a primary tuning circuit;
• a secondary tuning circuit;
• and
• first and second band selecting terminals to apply a changeover voltage that switches the primary tuning circuit and the secondary tuning circuit to a low-band television signal receiving mode or a high-band television signal receiving mode,
• wherein each of the primary tuning circuit and the secondary tuning circuit has:
• a varactor diode;
• a high-band receiving coil and a low-band receiving coil each having a first end and a second end and connected in series at the first end thereof;
• and
• a switching diode having a first end and a second end, the first end of the switching diode is connected with a connection point of the high-band receiving coil and the low-band receiving coil, the second end of the switching diode is grounded high-frequency-wise;
• the varactor diode is connected in parallel to the series combination of the high-band receiving coil and the low-band receiving coil, and the first end of the low-badnd receiving coil is grounded high-frequency-wise in the primary tuning circuit and the secondary tuning circuit;
• the second end of each of the switching diodes is connected DC-wise to the first band selecting terminal;
• the first end of the switching diode of one of the primary tuning circuit and the secondary tuning circuit is connected to the second band selecting terminal via a first resistor;
• and
• the first end of the switching diode of the other of the primary and secondary tuning circuits is connected to the second band selecting terminal DC-wise via the low-band receiving coil of the other of the primary and secondary tuning circuits, and
• wherein the first end of the switching diode in the other of the primary and secondary tuning circuits is connected to the second band selecting terminal via the low-band receiving coil and a second resistor in series.