% Author: Dr. Matthias Jung, DL9MJ
% Year: 2020
\begin{circuitikz}
    \draw[-Triangle](0.0,0.0) -- (5.0,0.0) node[anchor=north east] () {$f$};
    \draw[-Triangle](0.0,0.0) -- (0.0,3.0) node[anchor=north east] () {$U$} ;

    \draw [thick] plot [smooth, tension=1] coordinates {
        (0.80,0.1)
        (1.80,1.1)
        (2.50,2.5)
        (3.20,1.1)
        (4.20,0.1)
    };

    \draw [dashed] (2.5,0) -- (2.5,3);
\end{circuitikz}