| 摘要 |
In a three-band switching oscillator, a switching circuit is provided to switch the operating conditions of first and second voltage-controlled oscillator and to switching an oscillation frequency band of said first voltage-controlled oscillator, and is composed of a first switch for supplying a current to place the first voltage-controlled oscillator into operation, a second switch for supplying a current to place the second voltage-controlled oscillator into operation, and first and second switching terminals for receiving switching voltages. The switching circuit switches the first switch in accordance with a switching voltage inputted to the first switching terminal and switches an oscillation frequency band in accordance with a switching voltage inputted to the second switching terminal, while only when a high-level switching voltage is inputted to the second switching terminal, the second switch is placed into an open condition by a high-level switching voltage inputted to the first switching terminal and placed into a closed condition by a low-level switching voltage inputted thereto, and when a low-level switching voltage is inputted to the second switching terminal, the second switch is placed into the open condition irrespective of the switching voltage inputted to the first switching terminal.
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