Low-noise and high-rate front-end ASIC for APD detectors in STCF ECAL

This study presents a low-noise, high-rate front-end readout application-specific integrated circuit (ASIC) designed for the electromagnetic calorimeter (ECAL) of the Super Tau-Charm Facility (STCF). To address the high background-count rate in the STCF ECAL, the temporal features of signals are analyzed node-by-node along the chain of the analog front-end circuit. Then, the system is optimized to mitigate the pile-up effects and elevate the count rate to megahertz levels. First, a charge-sensitive amplifier (CSA) with a fast reset path is developed, enabling quick resetting when the output reaches the maximum amplitude. This prevents the CSA from entering a pulse-dead zone owing to amplifier saturation caused by the pile-up. Second, a high-order shaper with baseline holder circuits is improved to enhance the anti-pile-up capability while maintaining an effective noise-filtering performance. Third, a high-speed peak-detection and hold circuit with an asynchronous first-input-first-output buffer function is proposed to hold and read the piled-up signals of the shaper. The ASIC is designed and manufactured using a standard commercial 1P6M 0.18 mu m\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${0.18}\,{\upmu }\hbox {m}$$\end{document} mixed-signal CMOS process with a chip area of 2.4mmx1.6mm\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${2.4}\,\hbox {mm} \times {1.6}\,\hbox {mm}$$\end{document}. The measurement results demonstrate a dynamic range of 4-500 fC with a nonlinearity error below 1.5%\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\%$$\end{document}. For periodically distributed input signals, a count rate of 1.5 MHz/Ch is achieved with a peak time of 360 ns, resulting in an equivalent noise charge (ENC) of 2500e-\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${2500}\,\hbox {e}<^>{-}$$\end{document}. The maximum count rate is 4 MHz/Ch at a peak time of 120 ns. At a peak time of 1.68 mu s\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${1.68}\,{\upmu }\hbox {s}$$\end{document} with a 270 pF external capacitance, the minimum ENC is 1966e-\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${1966}\,\hbox {e}<^>{-}$$\end{document}, and the noise slope is 3.08e-/pF\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${3.08}\,\hbox {e}<^>{-}/\hbox {pF}$$\end{document}. The timing resolution is better than 125 ps at an input charge of 200 fC. The power consumption is 35 mW/Ch.