US Patent 7538718 Radar system

Detection of failure mode peculiar to a high-electron mobility transistor is available. A control circuit controls a gate voltage switching portion so that the gate voltage applied to a transistor may become a given checking voltage. The checking voltage may be set to a pinch-off-voltage of the transistor, for example. The control circuit detects a current value of the drain current flown when the checking voltage is applied, thereby detecting a failure of the transistor based on the current value. According to the present invention, since failure detection is made on the basis of the drain current value flown when the checking voltage set up apart from an operating voltage is applied as the gate voltage, failure mode which is peculiar to the high electron mobility transistor and which is hardly detectable in an ordinary operating state becomes detectable.