The present invention is used for amplifying-measuring weak electric current and is composed of micro-current amplifier and so on. The input stage of the micro-current amplifier is composed of differential type source-follower circuit in which high-resistance junction field-effect transistor pair is used and the low power consumption operational amplifier is used in the following operation. The micro-current amplifier uses form type backfeeding resistance expanding method and input cable suspension method. The present invention is high in input impedance, fine in symmetry, good in impact-resistant ability, better in reliability than MOSFET transistor. The noise index is less than 0.05 mv. The limit sensitivity may reach 10 to the minus sixteenth power A. The accuracy of the meter and its reliability is extremely improved and the power consumption is small. |