Low-current electronics schematic and design solutions for space plasma characteristics measurement

Measurement of the main characteristics of ionospheric plasma – concentration, temperature, velocity and its composition – is the problem of measuring ultra-low currents from a practical point of view. A low-current input stage based on a transimpedance amplifier suitable for measuring plasma characteristics using a Langmuir probe and a retarding potential analyzer is considered. The main problems and limitations affecting the dynamic range at very low currents are identified and ways to solve them are outlined. At the schematic level, various types of input stages of integrated operational amplifiers and their features affecting the choice of a suitable integrated circuit are listed, the input stage of the ADA4530–1 amplifier and the bootstrapping technique implemented in it are described. The importance of selecting low-leakage feedback switches is noted and the possibility of its further reduction using bootstrapping is demonstrated. At the design level, parasitic conductivity and dielectric absorption in insulating materials are considered, a printed circuit board material with good characteristics is mentioned, the use of guard rings and polygons for a radical reduction of circuit board leakage is described