| 摘要 |
PURPOSE:To capture the change in the frequency to be converted as a large voltage change and improve the accuracy of measurement by converting the charging current in the half period of the frequency to be converted to voltage by an operational amplifier. CONSTITUTION:A resistance R4 and a capacitor C4 are connected in parallel to the inversion input terminal and output terminal of an operational amplifier OP, and a summing point P is connected to the inversion input terminal and a reference potential point to a noninversion input terminal. If the potential of the point P is the same as that of the potential point Q, the average current from a power source E is proportional to a frequency f. The output E0 of a current-voltage converting circuit is E0=-R4I when input current I. Hence, as a whole, it is expressed by E0= -CER4f. Here, C is the capacity of a capacitor C1. This makes it possible to easily obtain the output amplitude of about several volts by regulating the resistance R4. Further, a lower output impedance is obtainable and therefore the voltmeter V of a low input impedance can be connected. |
