Electronic Design and Modeling of an Integrated Plasma Impedance Probe

This paper describes the electronic design of a plasma impedance probe under development for microsatellite applications. The designs primary innovation is the integration of matched analog-to-digital converters on a single chip for sampling the probe's current and voltage signals. A fast fourier transform (FFT) is performed by an off-chip FPGA to compute the probe's impedance. This provides a robust solution for determining the plasma impedance accurately. The use of matched ADCs decreases the instrument's sensitivity to imprecision and variation in the probe stimulus waveform and the FFT reduces sensitivity to transient spikes that proved disruptive in previous instruments. The major analog errors and parametric variations affecting the PIP instrument and its effect on the accuracy and precision of the impedance measurement are also studied.