一、引言测量1 pA 和1 μA范围内的小电流和1 pA以下的更小电流的经典系统采用了运算放大器和高反馈电阻。用一组高电阻器和继电器开关,可测量宽范围的小直流电流。反馈电阻依电流的大小而定,可以很高(10~(13)Ω或更高)。要减少漏电流,开关必须是高绝缘的,所有连接也必须仔细加以绝缘。很小量的杂质会降低性能或使测量系统不能工作。此外,继电器线圈的电感也引起问题。继 I. INTRODUCTION Classical systems that measure small currents in the 1 pA and 1 μA ranges and smaller currents below 1 pA use op amps and high feedback resistors. With a set of high resistor and relay switches, a wide range of small DC currents can be measured. The feedback resistance can be very high (10 ~ (13) Ω or higher depending on the current). To reduce the leakage current, the switch must be high-insulation and all connections must be carefully insulated. A small amount of impurities can degrade performance or disable the measurement system. In addition, the inductance of the relay coil also causes problems. Following