| 摘要 |
PURPOSE:To measure a high frequency with high accuracy by applying an AC input signal to which a DC bias voltage has been superposed, to a Josephson junction device, and deriving a frequency of an input signal from a bias voltage value at the time when an AC Josephson effect occurs. CONSTITUTION:A closed circuit is constituted by connecting in series a signal source 1 for applying an AC input signal VAC, to a Josephson junction device 2 and a current detector 3 each other through a superposing circuit 6 for superposing a bias voltage VDC. An output of the current detector 3 is connected to a measurement control circuit 4. Also, an output of the measurement control circuit 4 is connected to a variable voltage generating circuit 5, and an output of the variable voltage generating circuit 5 is connected to the superposing circuit 6. In this state, the measurement control circuit 4 brings a DC bias voltage from the variable voltage generating circuit 5 to a variable control based on the output of the current detector 3, and a frequency of the AC input signal is derived based on a bias voltage value by which an AC Josephson effect occurs.
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