\documentclass[border=5pt]{standalone}
\usepackage{circuitikz}

\begin{document}

\begin{circuitikz}
    \draw (-2, 0) to[C=$C_u$]++ (0, -2) node[ground]{};
    \draw (0, 0) to[C=$C_u$]++ (0, -2) to[switch, l=$D_1$]++ (0, -2) coordinate(end_1);
    \draw (2, 0) to[C=$2C_u$]++ (0, -2) to[switch, l=$D_2$]++ (0, -2);
    \draw (4, 0) to[C=$4C_u$]++ (0, -2) to[switch, l=$D_3$]++ (0, -2);
    \draw (6, 0) to[C=$8C_u$]++ (0, -2) to[switch, l=$D_4$]++ (0, -2);
    \draw (8, 0) to[C=$16C_u$]++ (0, -2) to[switch, l=$D_5$]++ (0, -2);
    \draw (10, 0) to[C=$32C_u$]++ (0, -2) to[switch, l=$D_6$]++ (0, -2);

    \draw (12, 0) to[C=$C_u$]++ (0, -2) to[switch, l=$D_7$]++ (0, -2);
    \draw (14, 0) to[C=$2C_u$]++ (0, -2) to[switch, l=$D_8$]++ (0, -2); 
    \draw (16, 0) to[C=$4C_u$]++ (0, -2) to[switch, l=$D_9$]++ (0, -2);
    \draw (18, 0) to[C=$8C_u$]++ (0, -2) to[switch, l=$D_{10}$]++ (0, -2);
    \draw (20, 0) to[C=$16C_u$]++ (0, -2) to[switch, l=$D_{11}$]++ (0, -2);
    \draw (22, 0) to[C=$32C_u$]++ (0, -2) to[switch, l=$D_{12}$]++ (0, -2) coordinate(end_2);

    \draw (-2, 0) to (10, 0) to[C=$\frac{64}{63}C_u$]++ (2, 0) to (22, 0) to[short,-*]++ (1, 0) node[right]{$V_o$};
    \draw (end_1) to (end_2) to[short, -*]++ (1, 0) node[right]{$V_{ref}$};
\end{circuitikz}

\end{document}