| 摘要 |
PURPOSE:To decrease the measuring time by improving a phase characteristic of a null amplifier by negative feedback so as to improve the measuring accuracy, to eliminate the need for a capacitor for preventing oscillation and to reduce the time constant of the measuring circuit. CONSTITUTION:An operational amplifier 1 to be measured and the null amplifier 2 in the measuring circuit are connected in cascade and resistors R21, R22 are connected between input and output terminals of the null amplifier 2 and between a DC power supply for null amplifier 17 and the input terminal respectively. Further, feedback resistors R4, R5 for the measuring system are connected between the input terminal and the output terminal of the measuring circuit. The phase characteristic curve of the null amplifier 2 is improved by betaA0 times being a product between the rate of feedback beta of the resistors R21, R22 and the DC open loop gain A0 by constituting the measuring circuit in this way. Then, the measuring accuracy of the measuring circuit is improved, the need for the capacitor for preventing oscillation is not required, the time constant of the circuit is decreased and the measuring time is decreased.
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