| 摘要 |
PURPOSE:To detect easily an abnormality, and to cope with the abnormality immediately by executing a decision of a fault by detecting a drain current of an FET switch. CONSTITUTION:A driving circuit 2 is operated by a control signal to a terminal 13, and a microwave signal supplied to an input terminal 11 is switched by FETs 41, 42 and sent out of an output terminal 12. When the FETs 41, 42 are turned on, a voltage drop is generated across a resistance 5, and it is detected by a drain current detecting circuit 3 and supplied to a deciding circuit 4, the correspondence to the control signal of the terminal 13 is checked by the deciding circuit, whether the FET switch is normal or abnormal is decided, and its signal is sent out of a terminal 14. Accordingly, whether the FET switch is normal or abnormal can be diagnosed, and in the event of an abnormality, switching to a stand-by route is executed quickly.
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