% Author: Dr. Matthias Jung, DL9MJ
% Year: 2020
\begin{circuitikz}
    \draw[-Triangle](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, black] (0,0) 
         [rounded corners=5mm] -- ++(0.5,0)
         [rounded corners=2mm] -- ++(1.25,2.5)
         [rounded corners=0mm] 
            sin ++(0.25, 0.25)
            cos ++(0.25,-0.25)
            sin ++(0.25,-0.25);

    \draw[thick, black] (5,0) 
         [rounded corners=5mm] -- ++(-0.5,0)
         [rounded corners=2mm] -- ++(-1.25,2.5)
         [rounded corners=0mm] 
            sin ++(-0.25, 0.25)
            cos ++(-0.25,-0.25)
            sin ++(-0.25,-0.25);

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