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一、引言在1PA到1μA范围内的电流通常认为是低电流;低于1PA的电流认为是极低电流;这样低的电流的例子是离子室产生的电流和流过光敏二极管的反向电流。过去已经发表了很多有关低直流电流测量方面的文章。经典的系统是以运算放大器为基础加上高反馈电阻。使用一排高电阻和一套继电器开关,以此来测量宽范围的低直流电流,反馈电阻取决于电流的幅值,可高达10~3Ω或更高。为使泄漏电流减到最小,开关必须具有高的绝缘,而且所有连接部份都必须非常小心地绝缘,即使非常少量的杂物也会降低性能
I. INTRODUCTION The current in the 1 PA to 1 μA range is generally considered low current; currents below 1 PA are considered very low current; examples of such low currents are the current generated in the ion chamber and the reverse current flowing through the photodiode. In the past, there have been many articles on low DC current measurement. The classic system is based on op amps with high feedback resistors. Using a row of high resistance and a set of relay switches, to measure a wide range of low DC current, feedback resistance depends on the current amplitude can be as high as 10 ~ 3Ω or higher. To minimize leakage current, the switch must have high insulation and all connections must be very carefully insulated, even very small amounts of debris can degrade performance