Design of a fA wide dynamic range ADC for current sensing

Current sensing is important in various applications. The Utopia 2 Application Specific Integrated Circuit (ASIC) was developed in AMS 0.35 μm\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\upmu \hbox {m}$$\end{document} technology for radiation monitoring based on ionization chambers. The ASIC is able to measure current equal to 1 femtoampere (fA) after active leakage current compensation. The compensation is achieved with a second dummy compensating channel that is matched to the measuring channel. The ASIC was also designed to cope with input currents that span over nine decades of dynamic range. The analog to digital conversion is performed with charge balancing and counting. The maximum current that is equal to 5 μA\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\upmu \hbox {A}$$\end{document} can be measured after the introduction of a second range. The system has been characterized at a certified laboratory and is able to sense currents from 1 fA up to 5 μA\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\upmu \hbox {A}$$\end{document}.