抄録
Response characteristics of a very low level DC current amplifier which has a very high feedback resistor (1010Ω) are studied numerically and experimentally from the viewpoint of high speed response. In experiments, a positive feedback circuit is proposed and examined to improve the transient response of the amplifier. As a result, the rise time of 30 μs at 20 pA ofthe current sesitivity was obtained, by using the positive feedback circuit. It is verified that, by adapting the positive feedback circuit without causing internal oscillation, the response time of the DC amplifier is substantially improved from one half to one eighth as compared with former methods, if the shielding of feedback circuit is good enough and the very high and pure feedback resistorsare available.
