| 摘要 |
PURPOSE:To eliminate the influence of distributed capacities and to obtain stable conversion characteristics by inserting a detecting circuit into a negative feedback loop from the output of a differential amplifier of which the inverted output is connected to a movable electrode to the inverted output. CONSTITUTION:A detecting circuit wherein diodes D1, D2 are arranged in mutually opposite directions is inserted into a negative feedback loop from the output of a differential amplifier A2 of which the inverted output is connected to a movable electrode MP to the inverted output. Therefore, no influences are given at all to AC negative feedback effect, and a feedback rate is determined by the resistance values of resistances R1, R2, and the gain of an amplifier A2. Hence, if the gain of the amplifier A2 is sufficiently high, the potential fluctuations in the electrode MP is suppressed by the negative feedback effect, and the potential of this point can be regarded roughly constant, thus the influence of distributed capacities is eliminated. By the inclusion of the diodes D1, D2 in the negative feedback loop, the change of characteristics of the diodes D1, D2 is suppressed. |
