A Simple Digitizing Front-end for Plasma Diagnostic Probes

A simple and low-cost digitizer front-end for plasma diagnostic probes is presented. The circuit, featuring three operational amplifier stages, is capable of digitizing low-currents spanning over a wide range with minimal effects of analog to digital converter's quantization noise. The circuit also features compensation techniques to account for offset errors due to circuit non-linearities and temperature drifts. The error analysis of the proposed circuit is also presented. The scheme was tested for a current range of 500 pA to 5
$\mu A$
. A nonlinearity of 0.534 % was obtained from the hardware prototype. The circuit is ideal for interfacing amperometric sensors in space applications, such as, the Retarding Potential Analyzers and Langmuir Probe, where high-speed measurement is required.