| 摘要 |
PURPOSE:To prevent the interference of unnecessary AC voltage, by connecting a resistor and a capacitor in parallel between one end of a coil of a tuning circuit comprising a varactor diode and the coil and ground, and providing a capacitor between one end of the coil and a DC control voltage. CONSTITUTION:A coil 3 is connected in parallel with a series circuit comprising a capacitor 1 and a varactor diode 2, and a DC control voltage is applied through a resistor 4 to control the resonance frequency of a tuning circuit. A resistor 9 and a capacitor 8 are connected between the coil 3 and ground and a capacitor 7 is connected between an ungrounded terminal and an input terminal of the DC control voltage. When an AC voltage is superimposed on the DC control voltage, the same phase of the AC voltage is applied to the varactor diode 2 through the capacitor 7, allowing to prevent the change in the resonance frequency. |
