| 摘要 |
PROBLEM TO BE SOLVED: To provide a signal input circuit that can select DC coupling or AC coupling with respect to a differential input signal and having a differential amplifier circuit to simply adjust its zero point and to provide a waveform observation device employing the signal input circuit. SOLUTION: The signal input circuit is provided with an attenuation resistor R1 and a voltage division resistor R3 connected in series between a signal input terminal X and a ground E, with a DC coupling setting/release switch S1 that is connected between a noninverting input terminal of a differential amplifier circuit A and a connecting point between the attenuation resistor and the voltage division resistor, with a series circuit consisting of an AC coupling capacitor C1 connected in parallel with the switch S1 and an AC coupling setting/release switch S3, and with a pull-down resistor R5 connected between the noninverting input terminal of the differential amplifier circuit and the ground E so as to make zero point adjustment of the differential amplifier circuit. The similar circuits to above are connected between a signal input terminal Y and an inverting input terminal of the differential amplifier circuit A.
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