| 摘要 |
PROBLEM TO BE SOLVED: To provide a protective circuit for protecting a guard buffer connected to a guard line in a DC measuring circuit for an IC tester. SOLUTION: With forward direction voltage of diodes D1-D4 in a guard buffer protective circuit 8 being VF, when the relationship between power-source voltages VA and VB and an external voltage VG is VB<VG, a forward- direction current (VG-VF-VB)/R2 flows in the diode D4, so that the output voltage of a voltage amplifier 5 which is a guard buffer is kept at VS=VO. If VA>VG, the forward-direction current (VA-VF-VG)/R1 flows in the diode D2 so that the output voltage of the voltage amplifier 5 which is a guard buffer is kept at VS=VO.
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