| 摘要 |
PURPOSE:To achieve observation at low impedance without exerting effect on the signal of a wire to be observed, by constituting a source follower circuit from the metal oxide semiconductive transistor connected to the wire to be observed. CONSTITUTION:The gate electrode 2 of a MOS transistor 21 is connected to a wire 3 to be observed and the drain electrode 24 of the transistor 21 is connected to a first power source wire 25 while a source electrode 26 is connected to a pad 27 and one terminal 29 of a current source circuit 28 and one terminal 30 of the current source circuit 28 is connected to a second current source 31. A signal to be observed is taken out from the source electrode 26 of the tranistor 21.
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