\documentclass{article}
\usepackage{circuitikz}
\begin{document}
\begin{center}
\begin{circuitikz}[american voltages]
\ctikzset{tripoles/mos style/arrows}
\ctikzset{logic ports/scale=0.6}
\ctikzset{blocks/scale=2}
\usetikzlibrary{automata,positioning}
\draw

    

    (0, 6.9) node[vdd]{$V_{DD}$}

    (0,6.5) node [pmos]{$M_1$}
    (0,2.25) node [nmos]{$M_2$}

    (-1, 6.5) node[ocirc]{\hspace{-2.5em}CLK}
    (-1, 2.25) node[ocirc]{\hspace{-2.5em}CLK}
    
    (0, 5.75) to (0, 5)

    (0, 5.5) to (0.9, 5.5)
    (1.5, 5.5) to (2.3, 5.5) node[circ]{\hspace{0.5em}Y}
    
    (1.25,5.5) node[not port, xscale=1.1] (not) {}

    (0, 1.5) node[ground]{}
    
    (-2, 4.75)node[circ]{\hspace{-2em}$N_1$} to (-1, 4.75)
    (-2, 4.25)node[circ]{\hspace{-2em}$N_2$} to (-1, 4.25)
    
    (-2, 3.25)node[circ]{\hspace{-2em}$N_n$} to (-1, 3.25)

    (0,4) node[twoportshape](start){\begin{tabular}{c}\vspace{0.5em} Pull-Down\\\vspace{-2em} Network \end{tabular}};

    (0, 5.5) to (start.north)
    
; 
\draw [loosely dotted](-1.75,4) --  (-1.75,3.5);
\end{circuitikz}
\end{center}
\end{document}