高速微小電流計の設計と製作

概要

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A designing and the construction of high speed pico-ammeter (HSPA) with feedback resistors (Rf) of 1011 and 1012Ω is described. The floating capacitance at the input and the distributed capacitance around the Rfcould be effectively compensated by using a guard method and compensating metal plates (4 pieces), respectively. The metal plates method is also capable of compensation for the non-uniformly distributed resistance of the Rf. Electronical circuits to reduce the Miller integration effect and to compensate the distributed capacitance by using a lag net-work were also employed. The characteristics of the HSPA was examined with use of square-waved electron emission current, and then the input capacitance including the input cable was about 70 pF. The rise times obtained were 0.4 and 0.7 ms for the Rf of 1011Ω for small and large (2/3full scale) signals, respectively. Those of 2.6 ms for the Rf of 1012Ω for large signal was also obtained. The noise characteristics and the use of MOS-FET associated with its protection techniques are also discussed.
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