Design of transimpedance amplifier for fast ion current detectors

Abstract

Analytical Instruments are used in the analysis and identification of newlinetrace level chemical compounds that are present in a chemical sample. During newlinethe operation, the chemical compounds are ionised and accelerated in the newlinepresence of high energy electric fields. These accelerated ions are then newlinedetected and collected. The collected ions carry a tiny current which carries newlinethe signature of the chemical compounds that are present in the sample. newlineOne class of analytical instruments like Ion Mobility Spectrometer newlineuse Faraday Cup Detector for detecting and collecting the ions. They find newlineapplications in the field of medical diagnostics, explosive detection, air and newlinewater pollution, ground water contamination, agriculture, industries etc. When newlinethe ions hit the Faraday Cup detectors, they generate a tiny current usually in newlinethe picoamperes range. The emanating signal is coupled multiple sources of newlinenoise. One important source of noise is the high detector capacitance. Since newlinethe capacitors are frequency dependent, these higher capacitances increase the newlinenoise with increase in frequency. In order to amplify these current signals, a newlinehigh gain precision transimpedance amplifier is required. newlineDesign of such amplifiers poses significant challenges because of newlinetheir stringent requirements. The signal is required to be amplified with 180 newlinedB transimpedance gain, 5 kHz bandwidth and less than 500 µVRMS output newlinevoltage noise. This work reports the design, development, fabrication and newlinemeasurement of transimpedance amplifier to meet these requirements. newlineThe work reported in the literature so far used transistor based or newlineapplication specific integrated circuit based or commercially available off-the newlineshelf operational amplifiers for such applications. newline