| 摘要 |
PURPOSE:To enable the operating condition of a Schmitt circuit to be judged by detecting such an input voltage value that a power supply current to a Schmitt circuit exceeds a prescribed threshold value. CONSTITUTION:A Schmitt circuit 10 is housed in an integrated circuit 15. A voltage with a temporally changing level is supplied to the circuit 15 and the voltage is supplied to the circuit 10 as an input voltage D. The value I of a power supply current to the circuit 10 is detected by a current judging device 17. A threshold value ITH determined in advance according to the values of a CMOS inverter punch through current and the like included in the circuit 10 is set to the judging device 17, which judges which of the value I of the power supply current and the threshold value ITH is larger than the other. A memory 18 stores the value of a voltage generated in a voltage generator 16 and a judged result in the judging device 17 while the two values are processed in association with each other. Thus, independently of the circuit operation of the integrated circuit 15 housing the Schmitt circuit 10, the operation test of the Schmitt circuit 10 included in the circuit 15 can be conducted.
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